| Message ID | 20221025151344.3784230-1-chao.p.peng@linux.intel.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: mm: fd-based approach for supporting KVM | expand |
On Tue, Oct 25, 2022 at 8:48 PM Chao Peng <chao.p.peng@linux.intel.com> wrote: > > This patch series implements KVM guest private memory for confidential > computing scenarios like Intel TDX[1]. If a TDX host accesses > TDX-protected guest memory, machine check can happen which can further > crash the running host system, this is terrible for multi-tenant > configurations. The host accesses include those from KVM userspace like > QEMU. This series addresses KVM userspace induced crash by introducing > new mm and KVM interfaces so KVM userspace can still manage guest memory > via a fd-based approach, but it can never access the guest memory > content. > > The patch series touches both core mm and KVM code. I appreciate > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other > reviews are always welcome. > - 01: mm change, target for mm tree > - 02-08: KVM change, target for KVM tree > > Given KVM is the only current user for the mm part, I have chatted with > Paolo and he is OK to merge the mm change through KVM tree, but > reviewed-by/acked-by is still expected from the mm people. > > The patches have been verified in Intel TDX environment, but Vishal has > done an excellent work on the selftests[4] which are dedicated for this > series, making it possible to test this series without innovative > hardware and fancy steps of building a VM environment. See Test section > below for more info. > > > Introduction > ============ > KVM userspace being able to crash the host is horrible. Under current > KVM architecture, all guest memory is inherently accessible from KVM > userspace and is exposed to the mentioned crash issue. The goal of this > series is to provide a solution to align mm and KVM, on a userspace > inaccessible approach of exposing guest memory. > > Normally, KVM populates secondary page table (e.g. EPT) by using a host > virtual address (hva) from core mm page table (e.g. x86 userspace page > table). This requires guest memory being mmaped into KVM userspace, but > this is also the source where the mentioned crash issue can happen. In > theory, apart from those 'shared' memory for device emulation etc, guest > memory doesn't have to be mmaped into KVM userspace. > > This series introduces fd-based guest memory which will not be mmaped > into KVM userspace. KVM populates secondary page table by using a With no mappings in place for userspace VMM, IIUC, looks like the host kernel will not be able to find the culprit userspace process in case of Machine check error on guest private memory. As implemented in hwpoison_user_mappings, host kernel tries to look at the processes which have mapped the pfns with hardware error. Is there a modification needed in mce handling logic of the host kernel to immediately send a signal to the vcpu thread accessing faulting pfn backing guest private memory? > fd/offset pair backed by a memory file system. The fd can be created > from a supported memory filesystem like tmpfs/hugetlbfs and KVM can > directly interact with them with newly introduced in-kernel interface, > therefore remove the KVM userspace from the path of accessing/mmaping > the guest memory. > > Kirill had a patch [2] to address the same issue in a different way. It > tracks guest encrypted memory at the 'struct page' level and relies on > HWPOISON to reject the userspace access. The patch has been discussed in > several online and offline threads and resulted in a design document [3] > which is also the original proposal for this series. Later this patch > series evolved as more comments received in community but the major > concepts in [3] still hold true so recommend reading. > > The patch series may also be useful for other usages, for example, pure > software approach may use it to harden itself against unintentional > access to guest memory. This series is designed with these usages in > mind but doesn't have code directly support them and extension might be > needed. > > > mm change > ========= > Introduces a new memfd_restricted system call which can create memory > file that is restricted from userspace access via normal MMU operations > like read(), write() or mmap() etc and the only way to use it is > passing it to a third kernel module like KVM and relying on it to > access the fd through the newly added restrictedmem kernel interface. > The restrictedmem interface bridges the memory file subsystems > (tmpfs/hugetlbfs etc) and their users (KVM in this case) and provides > bi-directional communication between them. > > > KVM change > ========== > Extends the KVM memslot to provide guest private (encrypted) memory from > a fd. With this extension, a single memslot can maintain both private > memory through private fd (restricted_fd/restricted_offset) and shared > (unencrypted) memory through userspace mmaped host virtual address > (userspace_addr). For a particular guest page, the corresponding page in > KVM memslot can be only either private or shared and only one of the > shared/private parts of the memslot is visible to guest. For how this > new extension is used in QEMU, please refer to kvm_set_phys_mem() in > below TDX-enabled QEMU repo. > > Introduces new KVM_EXIT_MEMORY_FAULT exit to allow userspace to get the > chance on decision-making for shared <-> private memory conversion. The > exit can be an implicit conversion in KVM page fault handler or an > explicit conversion from guest OS. > > Extends existing SEV ioctls KVM_MEMORY_ENCRYPT_{UN,}REG_REGION to > convert a guest page between private <-> shared. The data maintained in > these ioctls tells the truth whether a guest page is private or shared > and this information will be used in KVM page fault handler to decide > whether the private or the shared part of the memslot is visible to > guest. > > > Test > ==== > Ran two kinds of tests: > - Selftests [4] from Vishal and VM boot tests in non-TDX environment > Code also in below repo: https://github.com/chao-p/linux/tree/privmem-v9 > > - Functional tests in TDX capable environment > Tested the new functionalities in TDX environment. Code repos: > Linux: https://github.com/chao-p/linux/tree/privmem-v9-tdx > QEMU: https://github.com/chao-p/qemu/tree/privmem-v9 > > An example QEMU command line for TDX test: > -object tdx-guest,id=tdx,debug=off,sept-ve-disable=off \ > -machine confidential-guest-support=tdx \ > -object memory-backend-memfd-private,id=ram1,size=${mem} \ > -machine memory-backend=ram1 > > > TODO > ==== > - Page accounting and limiting for encrypted memory > - hugetlbfs support > > > Changelog > ========= > v9: > - mm: move inaccessible memfd into separated syscall. > - mm: return page instead of pfn_t for inaccessible_get_pfn and remove > inaccessible_put_pfn. > - KVM: rename inaccessible/private to restricted and CONFIG change to > make the code friendly to pKVM. > - KVM: add invalidate_begin/end pair to fix race contention and revise > the lock protection for invalidation path. > - KVM: optimize setting lpage_info for > 2M level by direct accessing > lower level's result. > - KVM: avoid load xarray in kvm_mmu_max_mapping_level() and instead let > the caller to pass in is_private. > - KVM: API doc improvement. > v8: > - mm: redesign mm part by introducing a shim layer(inaccessible_memfd) > in memfd to avoid touch the memory file systems directly. > - mm: exclude F_SEAL_AUTO_ALLOCATE as it is for shared memory and > cause confusion in this series, will send out separately. > - doc: exclude the man page change, it's not kernel patch and will > send out separately. > - KVM: adapt to use the new mm inaccessible_memfd interface. > - KVM: update lpage_info when setting mem_attr_array to support > large page. > - KVM: change from xa_store_range to xa_store for mem_attr_array due > to xa_store_range overrides all entries which is not intended > behavior for us. > - KVM: refine the mmu_invalidate_retry_gfn mechanism for private page. > - KVM: reorganize KVM_MEMORY_ENCRYPT_{UN,}REG_REGION and private page > handling code suggested by Sean. > v7: > - mm: introduce F_SEAL_AUTO_ALLOCATE to avoid double allocation. > - KVM: use KVM_MEMORY_ENCRYPT_{UN,}REG_REGION to record > private/shared info. > - KVM: use similar sync mechanism between zap/page fault paths as > mmu_notifier for memfile_notifier based invalidation. > v6: > - mm: introduce MEMFILE_F_* flags into memfile_node to allow checking > feature consistence among all memfile_notifier users and get rid of > internal flags like SHM_F_INACCESSIBLE. > - mm: make pfn_ops callbacks being members of memfile_backing_store > and then refer to it directly in memfile_notifier. > - mm: remove backing store unregister. > - mm: remove RLIMIT_MEMLOCK based memory accounting and limiting. > - KVM: reorganize patch sequence for page fault handling and private > memory enabling. > v5: > - Add man page for MFD_INACCESSIBLE flag and improve KVM API do for > the new memslot extensions. > - mm: introduce memfile_{un}register_backing_store to allow memory > backing store to register/unregister it from memfile_notifier. > - mm: remove F_SEAL_INACCESSIBLE, use in-kernel flag > (SHM_F_INACCESSIBLE for shmem) instead. > - mm: add memory accounting and limiting (RLIMIT_MEMLOCK based) for > MFD_INACCESSIBLE memory. > - KVM: remove the overlap check for mapping the same file+offset into > multiple gfns due to perf consideration, warned in document. > v4: > - mm: rename memfd_ops to memfile_notifier and separate it from > memfd.c to standalone memfile-notifier.c. > - KVM: move pfn_ops to per-memslot scope from per-vm scope and allow > registering multiple memslots to the same memory backing store. > - KVM: add a 'kvm' reference in memslot so that we can recover kvm in > memfile_notifier handlers. > - KVM: add 'private_' prefix for the new fields in memslot. > - KVM: reshape the 'type' to 'flag' for kvm_memory_exit > v3: > - Remove 'RFC' prefix. > - Fix race condition between memfile_notifier handlers and kvm destroy. > - mm: introduce MFD_INACCESSIBLE flag for memfd_create() to force > setting F_SEAL_INACCESSIBLE when the fd is created. > - KVM: add the shared part of the memslot back to make private/shared > pages live in one memslot. > > Reference > ========= > [1] Intel TDX: > https://www.intel.com/content/www/us/en/developer/articles/technical/intel-trust-domain-extensions.html > [2] Kirill's implementation: > https://lore.kernel.org/all/20210416154106.23721-1-kirill.shutemov@linux.intel.com/T/ > [3] Original design proposal: > https://lore.kernel.org/all/20210824005248.200037-1-seanjc@google.com/ > [4] Selftest: > https://lore.kernel.org/all/20220819174659.2427983-1-vannapurve@google.com/ > > > Chao Peng (7): > KVM: Extend the memslot to support fd-based private memory > KVM: Add KVM_EXIT_MEMORY_FAULT exit > KVM: Use gfn instead of hva for mmu_notifier_retry > KVM: Register/unregister the guest private memory regions > KVM: Update lpage info when private/shared memory are mixed > KVM: Handle page fault for private memory > KVM: Enable and expose KVM_MEM_PRIVATE > > Kirill A. Shutemov (1): > mm: Introduce memfd_restricted system call to create restricted user > memory > > Documentation/virt/kvm/api.rst | 88 ++++- > arch/x86/entry/syscalls/syscall_32.tbl | 1 + > arch/x86/entry/syscalls/syscall_64.tbl | 1 + > arch/x86/include/asm/kvm_host.h | 8 + > arch/x86/kvm/Kconfig | 3 + > arch/x86/kvm/mmu/mmu.c | 170 +++++++++- > arch/x86/kvm/mmu/mmu_internal.h | 14 +- > arch/x86/kvm/mmu/mmutrace.h | 1 + > arch/x86/kvm/mmu/spte.h | 6 + > arch/x86/kvm/mmu/tdp_mmu.c | 3 +- > arch/x86/kvm/x86.c | 4 +- > include/linux/kvm_host.h | 89 ++++- > include/linux/restrictedmem.h | 62 ++++ > include/linux/syscalls.h | 1 + > include/uapi/asm-generic/unistd.h | 5 +- > include/uapi/linux/kvm.h | 38 +++ > include/uapi/linux/magic.h | 1 + > kernel/sys_ni.c | 3 + > mm/Kconfig | 4 + > mm/Makefile | 1 + > mm/restrictedmem.c | 250 ++++++++++++++ > virt/kvm/Kconfig | 7 + > virt/kvm/kvm_main.c | 453 +++++++++++++++++++++---- > 23 files changed, 1121 insertions(+), 92 deletions(-) > create mode 100644 include/linux/restrictedmem.h > create mode 100644 mm/restrictedmem.c > > > base-commit: e18d6152ff0f41b7f01f9817372022df04e0d354 > -- > 2.25.1 >
On Thu, Nov 03, 2022 at 05:43:52PM +0530, Vishal Annapurve <vannapurve@google.com> wrote: > On Tue, Oct 25, 2022 at 8:48 PM Chao Peng <chao.p.peng@linux.intel.com> wrote: > > > > This patch series implements KVM guest private memory for confidential > > computing scenarios like Intel TDX[1]. If a TDX host accesses > > TDX-protected guest memory, machine check can happen which can further > > crash the running host system, this is terrible for multi-tenant > > configurations. The host accesses include those from KVM userspace like > > QEMU. This series addresses KVM userspace induced crash by introducing > > new mm and KVM interfaces so KVM userspace can still manage guest memory > > via a fd-based approach, but it can never access the guest memory > > content. > > > > The patch series touches both core mm and KVM code. I appreciate > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other > > reviews are always welcome. > > - 01: mm change, target for mm tree > > - 02-08: KVM change, target for KVM tree > > > > Given KVM is the only current user for the mm part, I have chatted with > > Paolo and he is OK to merge the mm change through KVM tree, but > > reviewed-by/acked-by is still expected from the mm people. > > > > The patches have been verified in Intel TDX environment, but Vishal has > > done an excellent work on the selftests[4] which are dedicated for this > > series, making it possible to test this series without innovative > > hardware and fancy steps of building a VM environment. See Test section > > below for more info. > > > > > > Introduction > > ============ > > KVM userspace being able to crash the host is horrible. Under current > > KVM architecture, all guest memory is inherently accessible from KVM > > userspace and is exposed to the mentioned crash issue. The goal of this > > series is to provide a solution to align mm and KVM, on a userspace > > inaccessible approach of exposing guest memory. > > > > Normally, KVM populates secondary page table (e.g. EPT) by using a host > > virtual address (hva) from core mm page table (e.g. x86 userspace page > > table). This requires guest memory being mmaped into KVM userspace, but > > this is also the source where the mentioned crash issue can happen. In > > theory, apart from those 'shared' memory for device emulation etc, guest > > memory doesn't have to be mmaped into KVM userspace. > > > > This series introduces fd-based guest memory which will not be mmaped > > into KVM userspace. KVM populates secondary page table by using a > > With no mappings in place for userspace VMM, IIUC, looks like the host > kernel will not be able to find the culprit userspace process in case > of Machine check error on guest private memory. As implemented in > hwpoison_user_mappings, host kernel tries to look at the processes > which have mapped the pfns with hardware error. > > Is there a modification needed in mce handling logic of the host > kernel to immediately send a signal to the vcpu thread accessing > faulting pfn backing guest private memory? mce_register_decode_chain() can be used. MCE physical address(p->mce_addr) includes host key id in addition to real physical address. By searching used hkid by KVM, we can determine if the page is assigned to guest TD or not. If yes, send SIGBUS. kvm_machine_check() can be enhanced for KVM specific use. This is before memory_failure() is called, though. any other ideas?
On Mon, Nov 07, 2022 at 04:41:41PM -0800, Isaku Yamahata wrote: > On Thu, Nov 03, 2022 at 05:43:52PM +0530, > Vishal Annapurve <vannapurve@google.com> wrote: > > > On Tue, Oct 25, 2022 at 8:48 PM Chao Peng <chao.p.peng@linux.intel.com> wrote: > > > > > > This patch series implements KVM guest private memory for confidential > > > computing scenarios like Intel TDX[1]. If a TDX host accesses > > > TDX-protected guest memory, machine check can happen which can further > > > crash the running host system, this is terrible for multi-tenant > > > configurations. The host accesses include those from KVM userspace like > > > QEMU. This series addresses KVM userspace induced crash by introducing > > > new mm and KVM interfaces so KVM userspace can still manage guest memory > > > via a fd-based approach, but it can never access the guest memory > > > content. > > > > > > The patch series touches both core mm and KVM code. I appreciate > > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other > > > reviews are always welcome. > > > - 01: mm change, target for mm tree > > > - 02-08: KVM change, target for KVM tree > > > > > > Given KVM is the only current user for the mm part, I have chatted with > > > Paolo and he is OK to merge the mm change through KVM tree, but > > > reviewed-by/acked-by is still expected from the mm people. > > > > > > The patches have been verified in Intel TDX environment, but Vishal has > > > done an excellent work on the selftests[4] which are dedicated for this > > > series, making it possible to test this series without innovative > > > hardware and fancy steps of building a VM environment. See Test section > > > below for more info. > > > > > > > > > Introduction > > > ============ > > > KVM userspace being able to crash the host is horrible. Under current > > > KVM architecture, all guest memory is inherently accessible from KVM > > > userspace and is exposed to the mentioned crash issue. The goal of this > > > series is to provide a solution to align mm and KVM, on a userspace > > > inaccessible approach of exposing guest memory. > > > > > > Normally, KVM populates secondary page table (e.g. EPT) by using a host > > > virtual address (hva) from core mm page table (e.g. x86 userspace page > > > table). This requires guest memory being mmaped into KVM userspace, but > > > this is also the source where the mentioned crash issue can happen. In > > > theory, apart from those 'shared' memory for device emulation etc, guest > > > memory doesn't have to be mmaped into KVM userspace. > > > > > > This series introduces fd-based guest memory which will not be mmaped > > > into KVM userspace. KVM populates secondary page table by using a > > > > With no mappings in place for userspace VMM, IIUC, looks like the host > > kernel will not be able to find the culprit userspace process in case > > of Machine check error on guest private memory. As implemented in > > hwpoison_user_mappings, host kernel tries to look at the processes > > which have mapped the pfns with hardware error. > > > > Is there a modification needed in mce handling logic of the host > > kernel to immediately send a signal to the vcpu thread accessing > > faulting pfn backing guest private memory? > > mce_register_decode_chain() can be used. MCE physical address(p->mce_addr) > includes host key id in addition to real physical address. By searching used > hkid by KVM, we can determine if the page is assigned to guest TD or not. If > yes, send SIGBUS. > > kvm_machine_check() can be enhanced for KVM specific use. This is before > memory_failure() is called, though. > > any other ideas? That's too KVM-centric. It will not work for other possible user of restricted memfd. I tried to find a way to get it right: we need to get restricted memfd code info about corrupted page so it can invalidate its users. On the next request of the page the user will see an error. In case of KVM, the error will likely escalate to SIGBUS. The problem is that core-mm code that handles memory failure knows nothing about restricted memfd. It only sees that the page belongs to a normal memfd. AFAICS, there's no way to get it intercepted from the shim level. shmem code has to be patches. shmem_error_remove_page() has to call into restricted memfd code. Hugh, are you okay with this? Or maybe you have a better idea?
Chao Peng <chao.p.peng@linux.intel.com> writes: <snip> > Introduction > ============ > KVM userspace being able to crash the host is horrible. Under current > KVM architecture, all guest memory is inherently accessible from KVM > userspace and is exposed to the mentioned crash issue. The goal of this > series is to provide a solution to align mm and KVM, on a userspace > inaccessible approach of exposing guest memory. > > Normally, KVM populates secondary page table (e.g. EPT) by using a host > virtual address (hva) from core mm page table (e.g. x86 userspace page > table). This requires guest memory being mmaped into KVM userspace, but > this is also the source where the mentioned crash issue can happen. In > theory, apart from those 'shared' memory for device emulation etc, guest > memory doesn't have to be mmaped into KVM userspace. > > This series introduces fd-based guest memory which will not be mmaped > into KVM userspace. KVM populates secondary page table by using a > fd/offset pair backed by a memory file system. The fd can be created > from a supported memory filesystem like tmpfs/hugetlbfs and KVM can > directly interact with them with newly introduced in-kernel interface, > therefore remove the KVM userspace from the path of accessing/mmaping > the guest memory. > > Kirill had a patch [2] to address the same issue in a different way. It > tracks guest encrypted memory at the 'struct page' level and relies on > HWPOISON to reject the userspace access. The patch has been discussed in > several online and offline threads and resulted in a design document [3] > which is also the original proposal for this series. Later this patch > series evolved as more comments received in community but the major > concepts in [3] still hold true so recommend reading. > > The patch series may also be useful for other usages, for example, pure > software approach may use it to harden itself against unintentional > access to guest memory. This series is designed with these usages in > mind but doesn't have code directly support them and extension might be > needed. There are a couple of additional use cases where having a consistent memory interface with the kernel would be useful. - Xen DomU guests providing other domains with VirtIO backends Xen by default doesn't give other domains special access to a domains memory. The guest can grant access to regions of its memory to other domains for this purpose. - pKVM on ARM Similar to Xen, pKVM moves the management of the page tables into the hypervisor and again doesn't allow those domains to share memory by default. - VirtIO loopback This allows for VirtIO devices for the host kernel to be serviced by backends running in userspace. Obviously the memory userspace is allowed to access is strictly limited to the buffers and queues because giving userspace unrestricted access to the host kernel would have consequences. All of these VirtIO backends work with vhost-user which uses memfds to pass references to guest memory from the VMM to the backend implementation. > mm change > ========= > Introduces a new memfd_restricted system call which can create memory > file that is restricted from userspace access via normal MMU operations > like read(), write() or mmap() etc and the only way to use it is > passing it to a third kernel module like KVM and relying on it to > access the fd through the newly added restrictedmem kernel interface. > The restrictedmem interface bridges the memory file subsystems > (tmpfs/hugetlbfs etc) and their users (KVM in this case) and provides > bi-directional communication between them. > > > KVM change > ========== > Extends the KVM memslot to provide guest private (encrypted) memory from > a fd. With this extension, a single memslot can maintain both private > memory through private fd (restricted_fd/restricted_offset) and shared > (unencrypted) memory through userspace mmaped host virtual address > (userspace_addr). For a particular guest page, the corresponding page in > KVM memslot can be only either private or shared and only one of the > shared/private parts of the memslot is visible to guest. For how this > new extension is used in QEMU, please refer to kvm_set_phys_mem() in > below TDX-enabled QEMU repo. > > Introduces new KVM_EXIT_MEMORY_FAULT exit to allow userspace to get the > chance on decision-making for shared <-> private memory conversion. The > exit can be an implicit conversion in KVM page fault handler or an > explicit conversion from guest OS. > > Extends existing SEV ioctls KVM_MEMORY_ENCRYPT_{UN,}REG_REGION to > convert a guest page between private <-> shared. The data maintained in > these ioctls tells the truth whether a guest page is private or shared > and this information will be used in KVM page fault handler to decide > whether the private or the shared part of the memslot is visible to > guest. > <snip>
On Wed, Nov 09, 2022 at 06:54:04PM +0300, Kirill A. Shutemov wrote: > On Mon, Nov 07, 2022 at 04:41:41PM -0800, Isaku Yamahata wrote: > > On Thu, Nov 03, 2022 at 05:43:52PM +0530, > > Vishal Annapurve <vannapurve@google.com> wrote: > > > > > On Tue, Oct 25, 2022 at 8:48 PM Chao Peng <chao.p.peng@linux.intel.com> wrote: > > > > > > > > This patch series implements KVM guest private memory for confidential > > > > computing scenarios like Intel TDX[1]. If a TDX host accesses > > > > TDX-protected guest memory, machine check can happen which can further > > > > crash the running host system, this is terrible for multi-tenant > > > > configurations. The host accesses include those from KVM userspace like > > > > QEMU. This series addresses KVM userspace induced crash by introducing > > > > new mm and KVM interfaces so KVM userspace can still manage guest memory > > > > via a fd-based approach, but it can never access the guest memory > > > > content. > > > > > > > > The patch series touches both core mm and KVM code. I appreciate > > > > Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other > > > > reviews are always welcome. > > > > - 01: mm change, target for mm tree > > > > - 02-08: KVM change, target for KVM tree > > > > > > > > Given KVM is the only current user for the mm part, I have chatted with > > > > Paolo and he is OK to merge the mm change through KVM tree, but > > > > reviewed-by/acked-by is still expected from the mm people. > > > > > > > > The patches have been verified in Intel TDX environment, but Vishal has > > > > done an excellent work on the selftests[4] which are dedicated for this > > > > series, making it possible to test this series without innovative > > > > hardware and fancy steps of building a VM environment. See Test section > > > > below for more info. > > > > > > > > > > > > Introduction > > > > ============ > > > > KVM userspace being able to crash the host is horrible. Under current > > > > KVM architecture, all guest memory is inherently accessible from KVM > > > > userspace and is exposed to the mentioned crash issue. The goal of this > > > > series is to provide a solution to align mm and KVM, on a userspace > > > > inaccessible approach of exposing guest memory. > > > > > > > > Normally, KVM populates secondary page table (e.g. EPT) by using a host > > > > virtual address (hva) from core mm page table (e.g. x86 userspace page > > > > table). This requires guest memory being mmaped into KVM userspace, but > > > > this is also the source where the mentioned crash issue can happen. In > > > > theory, apart from those 'shared' memory for device emulation etc, guest > > > > memory doesn't have to be mmaped into KVM userspace. > > > > > > > > This series introduces fd-based guest memory which will not be mmaped > > > > into KVM userspace. KVM populates secondary page table by using a > > > > > > With no mappings in place for userspace VMM, IIUC, looks like the host > > > kernel will not be able to find the culprit userspace process in case > > > of Machine check error on guest private memory. As implemented in > > > hwpoison_user_mappings, host kernel tries to look at the processes > > > which have mapped the pfns with hardware error. > > > > > > Is there a modification needed in mce handling logic of the host > > > kernel to immediately send a signal to the vcpu thread accessing > > > faulting pfn backing guest private memory? > > > > mce_register_decode_chain() can be used. MCE physical address(p->mce_addr) > > includes host key id in addition to real physical address. By searching used > > hkid by KVM, we can determine if the page is assigned to guest TD or not. If > > yes, send SIGBUS. > > > > kvm_machine_check() can be enhanced for KVM specific use. This is before > > memory_failure() is called, though. > > > > any other ideas? > > That's too KVM-centric. It will not work for other possible user of > restricted memfd. > > I tried to find a way to get it right: we need to get restricted memfd > code info about corrupted page so it can invalidate its users. On the next > request of the page the user will see an error. In case of KVM, the error > will likely escalate to SIGBUS. > > The problem is that core-mm code that handles memory failure knows nothing > about restricted memfd. It only sees that the page belongs to a normal > memfd. > > AFAICS, there's no way to get it intercepted from the shim level. shmem > code has to be patches. shmem_error_remove_page() has to call into > restricted memfd code. > > Hugh, are you okay with this? Or maybe you have a better idea? Okay, here is what I've come up with. It doesn't touch shmem code, but hooks up directly into memory-failure.c. It is still ugly, but should be tolerable. restrictedmem_error_page() loops over all restrictedmem inodes. It is slow, but memory failure is not hot path (I hope). Only build-tested. Chao, could you hook up ->error for KVM and get it tested? diff --git a/include/linux/restrictedmem.h b/include/linux/restrictedmem.h index 9c37c3ea3180..c2700c5daa43 100644 --- a/include/linux/restrictedmem.h +++ b/include/linux/restrictedmem.h @@ -12,6 +12,8 @@ struct restrictedmem_notifier_ops { pgoff_t start, pgoff_t end); void (*invalidate_end)(struct restrictedmem_notifier *notifier, pgoff_t start, pgoff_t end); + void (*error)(struct restrictedmem_notifier *notifier, + pgoff_t start, pgoff_t end); }; struct restrictedmem_notifier { @@ -34,6 +36,8 @@ static inline bool file_is_restrictedmem(struct file *file) return file->f_inode->i_sb->s_magic == RESTRICTEDMEM_MAGIC; } +void restrictedmem_error_page(struct page *page, struct address_space *mapping); + #else static inline void restrictedmem_register_notifier(struct file *file, @@ -57,6 +61,11 @@ static inline bool file_is_restrictedmem(struct file *file) return false; } +static inline void restrictedmem_error_page(struct page *page, + struct address_space *mapping) +{ +} + #endif /* CONFIG_RESTRICTEDMEM */ #endif /* _LINUX_RESTRICTEDMEM_H */ diff --git a/mm/memory-failure.c b/mm/memory-failure.c index e7ac570dda75..ee85e46c6992 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -62,6 +62,7 @@ #include <linux/page-isolation.h> #include <linux/pagewalk.h> #include <linux/shmem_fs.h> +#include <linux/restrictedmem.h> #include "swap.h" #include "internal.h" #include "ras/ras_event.h" @@ -939,6 +940,8 @@ static int me_pagecache_clean(struct page_state *ps, struct page *p) goto out; } + restrictedmem_error_page(p, mapping); + /* * The shmem page is kept in page cache instead of truncating * so is expected to have an extra refcount after error-handling. diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c index e5bf8907e0f8..0dcdff0d8055 100644 --- a/mm/restrictedmem.c +++ b/mm/restrictedmem.c @@ -29,6 +29,18 @@ static void restrictedmem_notifier_invalidate(struct restrictedmem_data *data, mutex_unlock(&data->lock); } +static void restrictedmem_notifier_error(struct restrictedmem_data *data, + pgoff_t start, pgoff_t end) +{ + struct restrictedmem_notifier *notifier; + + mutex_lock(&data->lock); + list_for_each_entry(notifier, &data->notifiers, list) { + notifier->ops->error(notifier, start, end); + } + mutex_unlock(&data->lock); +} + static int restrictedmem_release(struct inode *inode, struct file *file) { struct restrictedmem_data *data = inode->i_mapping->private_data; @@ -248,3 +260,30 @@ int restrictedmem_get_page(struct file *file, pgoff_t offset, return 0; } EXPORT_SYMBOL_GPL(restrictedmem_get_page); + +void restrictedmem_error_page(struct page *page, struct address_space *mapping) +{ + struct super_block *sb = restrictedmem_mnt->mnt_sb; + struct inode *inode, *next; + + if (!shmem_mapping(mapping)) + return; + + spin_lock(&sb->s_inode_list_lock); + list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) { + struct restrictedmem_data *data = inode->i_mapping->private_data; + struct file *memfd = data->memfd; + + if (memfd->f_mapping == mapping) { + pgoff_t start, end; + + spin_unlock(&sb->s_inode_list_lock); + + start = page->index; + end = start + thp_nr_pages(page); + restrictedmem_notifier_error(data, start, end); + return; + } + } + spin_unlock(&sb->s_inode_list_lock); +}
On Mon, Nov 14, 2022 at 11:43:37AM +0000, Alex Bennée wrote: > > Chao Peng <chao.p.peng@linux.intel.com> writes: > > <snip> > > Introduction > > ============ > > KVM userspace being able to crash the host is horrible. Under current > > KVM architecture, all guest memory is inherently accessible from KVM > > userspace and is exposed to the mentioned crash issue. The goal of this > > series is to provide a solution to align mm and KVM, on a userspace > > inaccessible approach of exposing guest memory. > > > > Normally, KVM populates secondary page table (e.g. EPT) by using a host > > virtual address (hva) from core mm page table (e.g. x86 userspace page > > table). This requires guest memory being mmaped into KVM userspace, but > > this is also the source where the mentioned crash issue can happen. In > > theory, apart from those 'shared' memory for device emulation etc, guest > > memory doesn't have to be mmaped into KVM userspace. > > > > This series introduces fd-based guest memory which will not be mmaped > > into KVM userspace. KVM populates secondary page table by using a > > fd/offset pair backed by a memory file system. The fd can be created > > from a supported memory filesystem like tmpfs/hugetlbfs and KVM can > > directly interact with them with newly introduced in-kernel interface, > > therefore remove the KVM userspace from the path of accessing/mmaping > > the guest memory. > > > > Kirill had a patch [2] to address the same issue in a different way. It > > tracks guest encrypted memory at the 'struct page' level and relies on > > HWPOISON to reject the userspace access. The patch has been discussed in > > several online and offline threads and resulted in a design document [3] > > which is also the original proposal for this series. Later this patch > > series evolved as more comments received in community but the major > > concepts in [3] still hold true so recommend reading. > > > > The patch series may also be useful for other usages, for example, pure > > software approach may use it to harden itself against unintentional > > access to guest memory. This series is designed with these usages in > > mind but doesn't have code directly support them and extension might be > > needed. > > There are a couple of additional use cases where having a consistent > memory interface with the kernel would be useful. Thanks very much for the info. But I'm not so confident that the current memfd_restricted() implementation can be useful for all these usages. > > - Xen DomU guests providing other domains with VirtIO backends > > Xen by default doesn't give other domains special access to a domains > memory. The guest can grant access to regions of its memory to other > domains for this purpose. I'm trying to form my understanding on how this could work and what's the benefit for a DomU guest to provide memory through memfd_restricted(). AFAICS, memfd_restricted() can help to hide the memory from DomU userspace, but I assume VirtIO backends are still in DomU uerspace and need access that memory, right? > > - pKVM on ARM > > Similar to Xen, pKVM moves the management of the page tables into the > hypervisor and again doesn't allow those domains to share memory by > default. Right, we already had some discussions on this in the past versions. > > - VirtIO loopback > > This allows for VirtIO devices for the host kernel to be serviced by > backends running in userspace. Obviously the memory userspace is > allowed to access is strictly limited to the buffers and queues > because giving userspace unrestricted access to the host kernel would > have consequences. Okay, but normal memfd_create() should work for it, right? And memfd_restricted() instead may not work as it unmaps the memory from userspace. > > All of these VirtIO backends work with vhost-user which uses memfds to > pass references to guest memory from the VMM to the backend > implementation. Sounds to me these are the places where normal memfd_create() can act on. VirtIO backends work on the mmap-ed memory which currently is not the case for memfd_restricted(). memfd_restricted() has different design purpose that unmaps the memory from userspace and employs some kernel callbacks so other kernel modules can make use of the memory with these callbacks instead of userspace virtual address. Chao > > > mm change > > ========= > > Introduces a new memfd_restricted system call which can create memory > > file that is restricted from userspace access via normal MMU operations > > like read(), write() or mmap() etc and the only way to use it is > > passing it to a third kernel module like KVM and relying on it to > > access the fd through the newly added restrictedmem kernel interface. > > The restrictedmem interface bridges the memory file subsystems > > (tmpfs/hugetlbfs etc) and their users (KVM in this case) and provides > > bi-directional communication between them. > > > > > > KVM change > > ========== > > Extends the KVM memslot to provide guest private (encrypted) memory from > > a fd. With this extension, a single memslot can maintain both private > > memory through private fd (restricted_fd/restricted_offset) and shared > > (unencrypted) memory through userspace mmaped host virtual address > > (userspace_addr). For a particular guest page, the corresponding page in > > KVM memslot can be only either private or shared and only one of the > > shared/private parts of the memslot is visible to guest. For how this > > new extension is used in QEMU, please refer to kvm_set_phys_mem() in > > below TDX-enabled QEMU repo. > > > > Introduces new KVM_EXIT_MEMORY_FAULT exit to allow userspace to get the > > chance on decision-making for shared <-> private memory conversion. The > > exit can be an implicit conversion in KVM page fault handler or an > > explicit conversion from guest OS. > > > > Extends existing SEV ioctls KVM_MEMORY_ENCRYPT_{UN,}REG_REGION to > > convert a guest page between private <-> shared. The data maintained in > > these ioctls tells the truth whether a guest page is private or shared > > and this information will be used in KVM page fault handler to decide > > whether the private or the shared part of the memslot is visible to > > guest. > > > <snip> > > -- > Alex Bennée
Chao Peng <chao.p.peng@linux.intel.com> writes: > On Mon, Nov 14, 2022 at 11:43:37AM +0000, Alex Bennée wrote: >> >> Chao Peng <chao.p.peng@linux.intel.com> writes: >> >> <snip> >> > Introduction >> > ============ >> > KVM userspace being able to crash the host is horrible. Under current >> > KVM architecture, all guest memory is inherently accessible from KVM >> > userspace and is exposed to the mentioned crash issue. The goal of this >> > series is to provide a solution to align mm and KVM, on a userspace >> > inaccessible approach of exposing guest memory. >> > >> > Normally, KVM populates secondary page table (e.g. EPT) by using a host >> > virtual address (hva) from core mm page table (e.g. x86 userspace page >> > table). This requires guest memory being mmaped into KVM userspace, but >> > this is also the source where the mentioned crash issue can happen. In >> > theory, apart from those 'shared' memory for device emulation etc, guest >> > memory doesn't have to be mmaped into KVM userspace. >> > >> > This series introduces fd-based guest memory which will not be mmaped >> > into KVM userspace. KVM populates secondary page table by using a >> > fd/offset pair backed by a memory file system. The fd can be created >> > from a supported memory filesystem like tmpfs/hugetlbfs and KVM can >> > directly interact with them with newly introduced in-kernel interface, >> > therefore remove the KVM userspace from the path of accessing/mmaping >> > the guest memory. >> > >> > Kirill had a patch [2] to address the same issue in a different way. It >> > tracks guest encrypted memory at the 'struct page' level and relies on >> > HWPOISON to reject the userspace access. The patch has been discussed in >> > several online and offline threads and resulted in a design document [3] >> > which is also the original proposal for this series. Later this patch >> > series evolved as more comments received in community but the major >> > concepts in [3] still hold true so recommend reading. >> > >> > The patch series may also be useful for other usages, for example, pure >> > software approach may use it to harden itself against unintentional >> > access to guest memory. This series is designed with these usages in >> > mind but doesn't have code directly support them and extension might be >> > needed. >> >> There are a couple of additional use cases where having a consistent >> memory interface with the kernel would be useful. > > Thanks very much for the info. But I'm not so confident that the current > memfd_restricted() implementation can be useful for all these usages. > >> >> - Xen DomU guests providing other domains with VirtIO backends >> >> Xen by default doesn't give other domains special access to a domains >> memory. The guest can grant access to regions of its memory to other >> domains for this purpose. > > I'm trying to form my understanding on how this could work and what's > the benefit for a DomU guest to provide memory through memfd_restricted(). > AFAICS, memfd_restricted() can help to hide the memory from DomU userspace, > but I assume VirtIO backends are still in DomU uerspace and need access > that memory, right? They need access to parts of the memory. At the moment you run your VirtIO domains in the Dom0 and give them access to the whole of a DomU's address space - however the Xen model is by default the guests memory is inaccessible to other domains on the system. The DomU guest uses the Xen grant model to expose portions of its address space to other domains - namely for the VirtIO queues themselves and any pages containing buffers involved in the VirtIO transaction. My thought was that looks like a guest memory interface which is mostly inaccessible (private) with some holes in it where memory is being explicitly shared with other domains. What I want to achieve is a common userspace API with defined semantics for what happens when private and shared regions are accessed. Because having each hypervisor/confidential computing architecture define its own special API for accessing this memory is just a recipe for fragmentation and makes sharing common VirtIO backends impossible. > >> >> - pKVM on ARM >> >> Similar to Xen, pKVM moves the management of the page tables into the >> hypervisor and again doesn't allow those domains to share memory by >> default. > > Right, we already had some discussions on this in the past versions. > >> >> - VirtIO loopback >> >> This allows for VirtIO devices for the host kernel to be serviced by >> backends running in userspace. Obviously the memory userspace is >> allowed to access is strictly limited to the buffers and queues >> because giving userspace unrestricted access to the host kernel would >> have consequences. > > Okay, but normal memfd_create() should work for it, right? And > memfd_restricted() instead may not work as it unmaps the memory from > userspace. > >> >> All of these VirtIO backends work with vhost-user which uses memfds to >> pass references to guest memory from the VMM to the backend >> implementation. > > Sounds to me these are the places where normal memfd_create() can act on. > VirtIO backends work on the mmap-ed memory which currently is not the > case for memfd_restricted(). memfd_restricted() has different design > purpose that unmaps the memory from userspace and employs some kernel > callbacks so other kernel modules can make use of the memory with these > callbacks instead of userspace virtual address. Maybe my understanding is backwards then. Are you saying a guest starts with all its memory exposed and then selectively unmaps the private regions? Is this driven by the VMM or the guest itself?
On Wed, Nov 16, 2022 at 09:40:23AM +0000, Alex Bennée wrote: > > Chao Peng <chao.p.peng@linux.intel.com> writes: > > > On Mon, Nov 14, 2022 at 11:43:37AM +0000, Alex Bennée wrote: > >> > >> Chao Peng <chao.p.peng@linux.intel.com> writes: > >> > >> <snip> > >> > Introduction > >> > ============ > >> > KVM userspace being able to crash the host is horrible. Under current > >> > KVM architecture, all guest memory is inherently accessible from KVM > >> > userspace and is exposed to the mentioned crash issue. The goal of this > >> > series is to provide a solution to align mm and KVM, on a userspace > >> > inaccessible approach of exposing guest memory. > >> > > >> > Normally, KVM populates secondary page table (e.g. EPT) by using a host > >> > virtual address (hva) from core mm page table (e.g. x86 userspace page > >> > table). This requires guest memory being mmaped into KVM userspace, but > >> > this is also the source where the mentioned crash issue can happen. In > >> > theory, apart from those 'shared' memory for device emulation etc, guest > >> > memory doesn't have to be mmaped into KVM userspace. > >> > > >> > This series introduces fd-based guest memory which will not be mmaped > >> > into KVM userspace. KVM populates secondary page table by using a > >> > fd/offset pair backed by a memory file system. The fd can be created > >> > from a supported memory filesystem like tmpfs/hugetlbfs and KVM can > >> > directly interact with them with newly introduced in-kernel interface, > >> > therefore remove the KVM userspace from the path of accessing/mmaping > >> > the guest memory. > >> > > >> > Kirill had a patch [2] to address the same issue in a different way. It > >> > tracks guest encrypted memory at the 'struct page' level and relies on > >> > HWPOISON to reject the userspace access. The patch has been discussed in > >> > several online and offline threads and resulted in a design document [3] > >> > which is also the original proposal for this series. Later this patch > >> > series evolved as more comments received in community but the major > >> > concepts in [3] still hold true so recommend reading. > >> > > >> > The patch series may also be useful for other usages, for example, pure > >> > software approach may use it to harden itself against unintentional > >> > access to guest memory. This series is designed with these usages in > >> > mind but doesn't have code directly support them and extension might be > >> > needed. > >> > >> There are a couple of additional use cases where having a consistent > >> memory interface with the kernel would be useful. > > > > Thanks very much for the info. But I'm not so confident that the current > > memfd_restricted() implementation can be useful for all these usages. > > > >> > >> - Xen DomU guests providing other domains with VirtIO backends > >> > >> Xen by default doesn't give other domains special access to a domains > >> memory. The guest can grant access to regions of its memory to other > >> domains for this purpose. > > > > I'm trying to form my understanding on how this could work and what's > > the benefit for a DomU guest to provide memory through memfd_restricted(). > > AFAICS, memfd_restricted() can help to hide the memory from DomU userspace, > > but I assume VirtIO backends are still in DomU uerspace and need access > > that memory, right? > > They need access to parts of the memory. At the moment you run your > VirtIO domains in the Dom0 and give them access to the whole of a DomU's > address space - however the Xen model is by default the guests memory is > inaccessible to other domains on the system. The DomU guest uses the Xen > grant model to expose portions of its address space to other domains - > namely for the VirtIO queues themselves and any pages containing buffers > involved in the VirtIO transaction. My thought was that looks like a > guest memory interface which is mostly inaccessible (private) with some > holes in it where memory is being explicitly shared with other domains. Yes, similar in conception. For KVM, memfd_restricted() is used by host OS, guest will issue conversion between private and shared for its memory range. This is similar to Xen DomU guest grants its memory to other domains. Similarly, I guess to make memfd_restricted() being really useful for Xen, it should be run on the VirtIO backend domain (e.g. equivalent to the host position for KVM). > > What I want to achieve is a common userspace API with defined semantics > for what happens when private and shared regions are accessed. Because > having each hypervisor/confidential computing architecture define its > own special API for accessing this memory is just a recipe for > fragmentation and makes sharing common VirtIO backends impossible. Yes, I agree. That's interesting to explore. > > > > >> > >> - pKVM on ARM > >> > >> Similar to Xen, pKVM moves the management of the page tables into the > >> hypervisor and again doesn't allow those domains to share memory by > >> default. > > > > Right, we already had some discussions on this in the past versions. > > > >> > >> - VirtIO loopback > >> > >> This allows for VirtIO devices for the host kernel to be serviced by > >> backends running in userspace. Obviously the memory userspace is > >> allowed to access is strictly limited to the buffers and queues > >> because giving userspace unrestricted access to the host kernel would > >> have consequences. > > > > Okay, but normal memfd_create() should work for it, right? And > > memfd_restricted() instead may not work as it unmaps the memory from > > userspace. > > > >> > >> All of these VirtIO backends work with vhost-user which uses memfds to > >> pass references to guest memory from the VMM to the backend > >> implementation. > > > > Sounds to me these are the places where normal memfd_create() can act on. > > VirtIO backends work on the mmap-ed memory which currently is not the > > case for memfd_restricted(). memfd_restricted() has different design > > purpose that unmaps the memory from userspace and employs some kernel > > callbacks so other kernel modules can make use of the memory with these > > callbacks instead of userspace virtual address. > > Maybe my understanding is backwards then. Are you saying a guest starts > with all its memory exposed and then selectively unmaps the private > regions? Is this driven by the VMM or the guest itself? For confidential computing usages, normally guest starts with all guest memory being private, e.g, cannot be accessed by host. The memory will be lived in memfd_restricted() memory and not exposed to host userspace VMM like QEMU. Guest then can selectively map its private sub regions (e.g. VirtIO queue in the guest VirtIO frontend driver) as shared so host backend driver in QEMU can see it. When this happens, new shared mapping will be established in KVM and the new memory will be provided from normal mmap-able memory, then QEMU can do whatever it can do for the device emulation. Thanks, Chao > > -- > Alex Bennée
This patch series implements KVM guest private memory for confidential computing scenarios like Intel TDX[1]. If a TDX host accesses TDX-protected guest memory, machine check can happen which can further crash the running host system, this is terrible for multi-tenant configurations. The host accesses include those from KVM userspace like QEMU. This series addresses KVM userspace induced crash by introducing new mm and KVM interfaces so KVM userspace can still manage guest memory via a fd-based approach, but it can never access the guest memory content. The patch series touches both core mm and KVM code. I appreciate Andrew/Hugh and Paolo/Sean can review and pick these patches. Any other reviews are always welcome. - 01: mm change, target for mm tree - 02-08: KVM change, target for KVM tree Given KVM is the only current user for the mm part, I have chatted with Paolo and he is OK to merge the mm change through KVM tree, but reviewed-by/acked-by is still expected from the mm people. The patches have been verified in Intel TDX environment, but Vishal has done an excellent work on the selftests[4] which are dedicated for this series, making it possible to test this series without innovative hardware and fancy steps of building a VM environment. See Test section below for more info. Introduction ============ KVM userspace being able to crash the host is horrible. Under current KVM architecture, all guest memory is inherently accessible from KVM userspace and is exposed to the mentioned crash issue. The goal of this series is to provide a solution to align mm and KVM, on a userspace inaccessible approach of exposing guest memory. Normally, KVM populates secondary page table (e.g. EPT) by using a host virtual address (hva) from core mm page table (e.g. x86 userspace page table). This requires guest memory being mmaped into KVM userspace, but this is also the source where the mentioned crash issue can happen. In theory, apart from those 'shared' memory for device emulation etc, guest memory doesn't have to be mmaped into KVM userspace. This series introduces fd-based guest memory which will not be mmaped into KVM userspace. KVM populates secondary page table by using a fd/offset pair backed by a memory file system. The fd can be created from a supported memory filesystem like tmpfs/hugetlbfs and KVM can directly interact with them with newly introduced in-kernel interface, therefore remove the KVM userspace from the path of accessing/mmaping the guest memory. Kirill had a patch [2] to address the same issue in a different way. It tracks guest encrypted memory at the 'struct page' level and relies on HWPOISON to reject the userspace access. The patch has been discussed in several online and offline threads and resulted in a design document [3] which is also the original proposal for this series. Later this patch series evolved as more comments received in community but the major concepts in [3] still hold true so recommend reading. The patch series may also be useful for other usages, for example, pure software approach may use it to harden itself against unintentional access to guest memory. This series is designed with these usages in mind but doesn't have code directly support them and extension might be needed. mm change ========= Introduces a new memfd_restricted system call which can create memory file that is restricted from userspace access via normal MMU operations like read(), write() or mmap() etc and the only way to use it is passing it to a third kernel module like KVM and relying on it to access the fd through the newly added restrictedmem kernel interface. The restrictedmem interface bridges the memory file subsystems (tmpfs/hugetlbfs etc) and their users (KVM in this case) and provides bi-directional communication between them. KVM change ========== Extends the KVM memslot to provide guest private (encrypted) memory from a fd. With this extension, a single memslot can maintain both private memory through private fd (restricted_fd/restricted_offset) and shared (unencrypted) memory through userspace mmaped host virtual address (userspace_addr). For a particular guest page, the corresponding page in KVM memslot can be only either private or shared and only one of the shared/private parts of the memslot is visible to guest. For how this new extension is used in QEMU, please refer to kvm_set_phys_mem() in below TDX-enabled QEMU repo. Introduces new KVM_EXIT_MEMORY_FAULT exit to allow userspace to get the chance on decision-making for shared <-> private memory conversion. The exit can be an implicit conversion in KVM page fault handler or an explicit conversion from guest OS. Extends existing SEV ioctls KVM_MEMORY_ENCRYPT_{UN,}REG_REGION to convert a guest page between private <-> shared. The data maintained in these ioctls tells the truth whether a guest page is private or shared and this information will be used in KVM page fault handler to decide whether the private or the shared part of the memslot is visible to guest. Test ==== Ran two kinds of tests: - Selftests [4] from Vishal and VM boot tests in non-TDX environment Code also in below repo: https://github.com/chao-p/linux/tree/privmem-v9 - Functional tests in TDX capable environment Tested the new functionalities in TDX environment. Code repos: Linux: https://github.com/chao-p/linux/tree/privmem-v9-tdx QEMU: https://github.com/chao-p/qemu/tree/privmem-v9 An example QEMU command line for TDX test: -object tdx-guest,id=tdx,debug=off,sept-ve-disable=off \ -machine confidential-guest-support=tdx \ -object memory-backend-memfd-private,id=ram1,size=${mem} \ -machine memory-backend=ram1 TODO ==== - Page accounting and limiting for encrypted memory - hugetlbfs support Changelog ========= v9: - mm: move inaccessible memfd into separated syscall. - mm: return page instead of pfn_t for inaccessible_get_pfn and remove inaccessible_put_pfn. - KVM: rename inaccessible/private to restricted and CONFIG change to make the code friendly to pKVM. - KVM: add invalidate_begin/end pair to fix race contention and revise the lock protection for invalidation path. - KVM: optimize setting lpage_info for > 2M level by direct accessing lower level's result. - KVM: avoid load xarray in kvm_mmu_max_mapping_level() and instead let the caller to pass in is_private. - KVM: API doc improvement. v8: - mm: redesign mm part by introducing a shim layer(inaccessible_memfd) in memfd to avoid touch the memory file systems directly. - mm: exclude F_SEAL_AUTO_ALLOCATE as it is for shared memory and cause confusion in this series, will send out separately. - doc: exclude the man page change, it's not kernel patch and will send out separately. - KVM: adapt to use the new mm inaccessible_memfd interface. - KVM: update lpage_info when setting mem_attr_array to support large page. - KVM: change from xa_store_range to xa_store for mem_attr_array due to xa_store_range overrides all entries which is not intended behavior for us. - KVM: refine the mmu_invalidate_retry_gfn mechanism for private page. - KVM: reorganize KVM_MEMORY_ENCRYPT_{UN,}REG_REGION and private page handling code suggested by Sean. v7: - mm: introduce F_SEAL_AUTO_ALLOCATE to avoid double allocation. - KVM: use KVM_MEMORY_ENCRYPT_{UN,}REG_REGION to record private/shared info. - KVM: use similar sync mechanism between zap/page fault paths as mmu_notifier for memfile_notifier based invalidation. v6: - mm: introduce MEMFILE_F_* flags into memfile_node to allow checking feature consistence among all memfile_notifier users and get rid of internal flags like SHM_F_INACCESSIBLE. - mm: make pfn_ops callbacks being members of memfile_backing_store and then refer to it directly in memfile_notifier. - mm: remove backing store unregister. - mm: remove RLIMIT_MEMLOCK based memory accounting and limiting. - KVM: reorganize patch sequence for page fault handling and private memory enabling. v5: - Add man page for MFD_INACCESSIBLE flag and improve KVM API do for the new memslot extensions. - mm: introduce memfile_{un}register_backing_store to allow memory backing store to register/unregister it from memfile_notifier. - mm: remove F_SEAL_INACCESSIBLE, use in-kernel flag (SHM_F_INACCESSIBLE for shmem) instead. - mm: add memory accounting and limiting (RLIMIT_MEMLOCK based) for MFD_INACCESSIBLE memory. - KVM: remove the overlap check for mapping the same file+offset into multiple gfns due to perf consideration, warned in document. v4: - mm: rename memfd_ops to memfile_notifier and separate it from memfd.c to standalone memfile-notifier.c. - KVM: move pfn_ops to per-memslot scope from per-vm scope and allow registering multiple memslots to the same memory backing store. - KVM: add a 'kvm' reference in memslot so that we can recover kvm in memfile_notifier handlers. - KVM: add 'private_' prefix for the new fields in memslot. - KVM: reshape the 'type' to 'flag' for kvm_memory_exit v3: - Remove 'RFC' prefix. - Fix race condition between memfile_notifier handlers and kvm destroy. - mm: introduce MFD_INACCESSIBLE flag for memfd_create() to force setting F_SEAL_INACCESSIBLE when the fd is created. - KVM: add the shared part of the memslot back to make private/shared pages live in one memslot. Reference ========= [1] Intel TDX: https://www.intel.com/content/www/us/en/developer/articles/technical/intel-trust-domain-extensions.html [2] Kirill's implementation: https://lore.kernel.org/all/20210416154106.23721-1-kirill.shutemov@linux.intel.com/T/ [3] Original design proposal: https://lore.kernel.org/all/20210824005248.200037-1-seanjc@google.com/ [4] Selftest: https://lore.kernel.org/all/20220819174659.2427983-1-vannapurve@google.com/ Chao Peng (7): KVM: Extend the memslot to support fd-based private memory KVM: Add KVM_EXIT_MEMORY_FAULT exit KVM: Use gfn instead of hva for mmu_notifier_retry KVM: Register/unregister the guest private memory regions KVM: Update lpage info when private/shared memory are mixed KVM: Handle page fault for private memory KVM: Enable and expose KVM_MEM_PRIVATE Kirill A. Shutemov (1): mm: Introduce memfd_restricted system call to create restricted user memory Documentation/virt/kvm/api.rst | 88 ++++- arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/x86/include/asm/kvm_host.h | 8 + arch/x86/kvm/Kconfig | 3 + arch/x86/kvm/mmu/mmu.c | 170 +++++++++- arch/x86/kvm/mmu/mmu_internal.h | 14 +- arch/x86/kvm/mmu/mmutrace.h | 1 + arch/x86/kvm/mmu/spte.h | 6 + arch/x86/kvm/mmu/tdp_mmu.c | 3 +- arch/x86/kvm/x86.c | 4 +- include/linux/kvm_host.h | 89 ++++- include/linux/restrictedmem.h | 62 ++++ include/linux/syscalls.h | 1 + include/uapi/asm-generic/unistd.h | 5 +- include/uapi/linux/kvm.h | 38 +++ include/uapi/linux/magic.h | 1 + kernel/sys_ni.c | 3 + mm/Kconfig | 4 + mm/Makefile | 1 + mm/restrictedmem.c | 250 ++++++++++++++ virt/kvm/Kconfig | 7 + virt/kvm/kvm_main.c | 453 +++++++++++++++++++++---- 23 files changed, 1121 insertions(+), 92 deletions(-) create mode 100644 include/linux/restrictedmem.h create mode 100644 mm/restrictedmem.c base-commit: e18d6152ff0f41b7f01f9817372022df04e0d354