| Message ID | 20250129172320.950523-4-tabba@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | KVM: Mapping guest_memfd backed memory at the host for software protected VMs | expand |
On 29.01.25 18:23, Fuad Tabba wrote: > Add support for mmap() and fault() for guest_memfd backed memory > in the host for VMs that support in-place conversion between > shared and private (shared memory). To that end, this patch adds > the ability to check whether the VM type has that support, and > only allows mapping its memory if that's the case. > > Additionally, this behavior is gated with a new configuration > option, CONFIG_KVM_GMEM_SHARED_MEM. > > Signed-off-by: Fuad Tabba <tabba@google.com> > > --- > > This patch series will allow shared memory support for software > VMs in x86. It will also introduce a similar VM type for arm64 > and allow shared memory support for that. In the future, pKVM > will also support shared memory. > --- > include/linux/kvm_host.h | 11 ++++++ > virt/kvm/Kconfig | 4 +++ > virt/kvm/guest_memfd.c | 77 ++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 92 insertions(+) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 401439bb21e3..408429f13bf4 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -717,6 +717,17 @@ static inline bool kvm_arch_has_private_mem(struct kvm *kvm) > } > #endif > > +/* > + * Arch code must define kvm_arch_gmem_supports_shared_mem if support for > + * private memory is enabled and it supports in-place shared/private conversion. > + */ > +#if !defined(kvm_arch_gmem_supports_shared_mem) && !IS_ENABLED(CONFIG_KVM_PRIVATE_MEM) > +static inline bool kvm_arch_gmem_supports_shared_mem(struct kvm *kvm) > +{ > + return false; > +} > +#endif > + > #ifndef kvm_arch_has_readonly_mem > static inline bool kvm_arch_has_readonly_mem(struct kvm *kvm) > { > diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig > index 54e959e7d68f..4e759e8020c5 100644 > --- a/virt/kvm/Kconfig > +++ b/virt/kvm/Kconfig > @@ -124,3 +124,7 @@ config HAVE_KVM_ARCH_GMEM_PREPARE > config HAVE_KVM_ARCH_GMEM_INVALIDATE > bool > depends on KVM_PRIVATE_MEM > + > +config KVM_GMEM_SHARED_MEM > + select KVM_PRIVATE_MEM > + bool > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 47a9f68f7b24..86441581c9ae 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -307,7 +307,84 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn) > return gfn - slot->base_gfn + slot->gmem.pgoff; > } > > +#ifdef CONFIG_KVM_GMEM_SHARED_MEM > +static vm_fault_t kvm_gmem_fault(struct vm_fault *vmf) > +{ > + struct inode *inode = file_inode(vmf->vma->vm_file); > + struct folio *folio; > + vm_fault_t ret = VM_FAULT_LOCKED; > + > + filemap_invalidate_lock_shared(inode->i_mapping); > + > + folio = kvm_gmem_get_folio(inode, vmf->pgoff); > + if (IS_ERR(folio)) { > + ret = VM_FAULT_SIGBUS; > + goto out_filemap; > + } > + > + if (folio_test_hwpoison(folio)) { > + ret = VM_FAULT_HWPOISON; > + goto out_folio; > + } > + Worth adding a comment, something like /* * Only private folios are marked as "guestmem" so far, and we never * expect private folios at this point. */ > + if (WARN_ON_ONCE(folio_test_guestmem(folio))) { > + ret = VM_FAULT_SIGBUS; > + goto out_folio; > + } > + > + /* No support for huge pages. */ > + if (WARN_ON_ONCE(folio_nr_pages(folio) > 1)) { > + ret = VM_FAULT_SIGBUS; > + goto out_folio; > + } > + /* We only support mmap of small folios. */ VM_WARN_ON_ONCE(folio_test_large(folio)); > + if (!folio_test_uptodate(folio)) { > + clear_highpage(folio_page(folio, 0)); > + folio_mark_uptodate(folio); > + } > + > + vmf->page = folio_file_page(folio, vmf->pgoff); > + Apart from that LGTM.
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 401439bb21e3..408429f13bf4 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -717,6 +717,17 @@ static inline bool kvm_arch_has_private_mem(struct kvm *kvm) } #endif +/* + * Arch code must define kvm_arch_gmem_supports_shared_mem if support for + * private memory is enabled and it supports in-place shared/private conversion. + */ +#if !defined(kvm_arch_gmem_supports_shared_mem) && !IS_ENABLED(CONFIG_KVM_PRIVATE_MEM) +static inline bool kvm_arch_gmem_supports_shared_mem(struct kvm *kvm) +{ + return false; +} +#endif + #ifndef kvm_arch_has_readonly_mem static inline bool kvm_arch_has_readonly_mem(struct kvm *kvm) { diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig index 54e959e7d68f..4e759e8020c5 100644 --- a/virt/kvm/Kconfig +++ b/virt/kvm/Kconfig @@ -124,3 +124,7 @@ config HAVE_KVM_ARCH_GMEM_PREPARE config HAVE_KVM_ARCH_GMEM_INVALIDATE bool depends on KVM_PRIVATE_MEM + +config KVM_GMEM_SHARED_MEM + select KVM_PRIVATE_MEM + bool diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 47a9f68f7b24..86441581c9ae 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -307,7 +307,84 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn) return gfn - slot->base_gfn + slot->gmem.pgoff; } +#ifdef CONFIG_KVM_GMEM_SHARED_MEM +static vm_fault_t kvm_gmem_fault(struct vm_fault *vmf) +{ + struct inode *inode = file_inode(vmf->vma->vm_file); + struct folio *folio; + vm_fault_t ret = VM_FAULT_LOCKED; + + filemap_invalidate_lock_shared(inode->i_mapping); + + folio = kvm_gmem_get_folio(inode, vmf->pgoff); + if (IS_ERR(folio)) { + ret = VM_FAULT_SIGBUS; + goto out_filemap; + } + + if (folio_test_hwpoison(folio)) { + ret = VM_FAULT_HWPOISON; + goto out_folio; + } + + if (WARN_ON_ONCE(folio_test_guestmem(folio))) { + ret = VM_FAULT_SIGBUS; + goto out_folio; + } + + /* No support for huge pages. */ + if (WARN_ON_ONCE(folio_nr_pages(folio) > 1)) { + ret = VM_FAULT_SIGBUS; + goto out_folio; + } + + if (!folio_test_uptodate(folio)) { + clear_highpage(folio_page(folio, 0)); + folio_mark_uptodate(folio); + } + + vmf->page = folio_file_page(folio, vmf->pgoff); + +out_folio: + if (ret != VM_FAULT_LOCKED) { + folio_unlock(folio); + folio_put(folio); + } + +out_filemap: + filemap_invalidate_unlock_shared(inode->i_mapping); + + return ret; +} + +static const struct vm_operations_struct kvm_gmem_vm_ops = { + .fault = kvm_gmem_fault, +}; + +static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma) +{ + struct kvm_gmem *gmem = file->private_data; + + if (!kvm_arch_gmem_supports_shared_mem(gmem->kvm)) + return -ENODEV; + + if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) != + (VM_SHARED | VM_MAYSHARE)) { + return -EINVAL; + } + + file_accessed(file); + vm_flags_set(vma, VM_DONTDUMP); + vma->vm_ops = &kvm_gmem_vm_ops; + + return 0; +} +#else +#define kvm_gmem_mmap NULL +#endif /* CONFIG_KVM_GMEM_SHARED_MEM */ + static struct file_operations kvm_gmem_fops = { + .mmap = kvm_gmem_mmap, .open = generic_file_open, .release = kvm_gmem_release, .fallocate = kvm_gmem_fallocate,
Add support for mmap() and fault() for guest_memfd backed memory in the host for VMs that support in-place conversion between shared and private (shared memory). To that end, this patch adds the ability to check whether the VM type has that support, and only allows mapping its memory if that's the case. Additionally, this behavior is gated with a new configuration option, CONFIG_KVM_GMEM_SHARED_MEM. Signed-off-by: Fuad Tabba <tabba@google.com> --- This patch series will allow shared memory support for software VMs in x86. It will also introduce a similar VM type for arm64 and allow shared memory support for that. In the future, pKVM will also support shared memory. --- include/linux/kvm_host.h | 11 ++++++ virt/kvm/Kconfig | 4 +++ virt/kvm/guest_memfd.c | 77 ++++++++++++++++++++++++++++++++++++++++ 3 files changed, 92 insertions(+)