| Message ID | 20240726185157.72821-1-pbonzini@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: guest_memfd: lazy preparation of pages + prefault support for SEV-SNP | expand |
On Fri, Jul 26, 2024 at 02:51:43PM -0400, Paolo Bonzini wrote: > Paolo Bonzini (14): > KVM: x86: disallow pre-fault for SNP VMs before initialization > KVM: guest_memfd: return folio from __kvm_gmem_get_pfn() > KVM: guest_memfd: delay folio_mark_uptodate() until after successful > preparation > KVM: guest_memfd: do not go through struct page > KVM: rename CONFIG_HAVE_KVM_GMEM_* to CONFIG_HAVE_KVM_ARCH_GMEM_* > KVM: guest_memfd: return locked folio from __kvm_gmem_get_pfn > KVM: guest_memfd: delay kvm_gmem_prepare_folio() until the memory is > passed to the guest > KVM: guest_memfd: make kvm_gmem_prepare_folio() operate on a single > struct kvm > KVM: remove kvm_arch_gmem_prepare_needed() > KVM: guest_memfd: move check for already-populated page to common code > KVM: cleanup and add shortcuts to kvm_range_has_memory_attributes() > KVM: extend kvm_range_has_memory_attributes() to check subset of > attributes > KVM: guest_memfd: let kvm_gmem_populate() operate only on private gfns > KVM: guest_memfd: abstract how prepared folios are recorded Re-tested series with multiple SNP guests with/without experimental THP patches on top. Also re-tested using the following SNP self tests (I believe Pratik has a newer version he'll be submitting soon): https://github.com/mdroth/linux/commits/snp-uptodate2-kst4/ x86_64/coco_pre_fault_memory_test Series: Tested-by: Michael Roth <michael.roth@amd.com> > > v1->v2: > - patch 1: new > - patch 7: point out benign race between page fault and hole-punch > - patch 7: clean up comments > - patch 10: clean up commit message > - patch 11: remove ";;" > - patch 13: fix length argument to kvm_range_has_memory_attributes() > - patch 14: new > > Documentation/virt/kvm/api.rst | 6 + > arch/x86/include/asm/kvm_host.h | 1 + > arch/x86/kvm/Kconfig | 4 +- > arch/x86/kvm/mmu/mmu.c | 5 +- > arch/x86/kvm/svm/sev.c | 17 +-- > arch/x86/kvm/svm/svm.c | 1 + > arch/x86/kvm/x86.c | 12 +- > include/linux/kvm_host.h | 9 +- > virt/kvm/Kconfig | 4 +- > virt/kvm/guest_memfd.c | 226 +++++++++++++++++++------------- > virt/kvm/kvm_main.c | 73 +++++------ > 11 files changed, 206 insertions(+), 152 deletions(-) > > -- > 2.43.0 > >
There are a few issues with the implementation of SEV page "preparation" and KVM_SEV_SNP_LAUNCH_UPDATE: - doing fallocate() before KVM_SEV_SNP_LAUNCH_UPDATE will cause the latter to fail. - checking that only private pages are passed to KVM_SEV_SNP_LAUNCH_UPDATE is done in the guts of vendor code, as is the check that pages are not passed twice. This goes against the idea of putting as much common code as possible in kvm_gmem_populate(), for example it returns -EINVAL if the page is already assigned. - clearing the page is unnecessary if the firmware will overwrite it - the "prepare" bool argument is kinda gross The important observation here is that the two paths that initialize the contents of the folio are mutually exclusive: either the folio is populated with unencrypted data by userspace, or it is zeroed because userspace did not do anything beyond fallocate(). But in the latter there's no need to zero and prepare the page at the time of fallocate(): it can be done instead when the guest actually uses the page. Pulling all the zero-and-prepare code into kvm_gmem_get_pfn() separates the flows more clearly, but how do you recognize folios that haven't been prepared yet? The answer is to use the up-to-date flag; there is a limited attempt to use it right now, but it only concerns itself with the folio having been cleared. Instead after this series the flag is set for folios that went through either kvm_gmem_populate() or that have been mapped into the guest once (and thus went through kvm_arch_gmem_prepare(), on architectures where that is a thing). As a bonus, KVM knows exactly which guest is mapping a page, and thus the preparation code does not have to iterate through all bound instances of "struct kvm". There is an easy way vendor-independent way to obtain the previous behavior if desired, and that is simply to do KVM_PRE_FAULT_MEMORY after KVM_SEV_SNP_LAUNCH_FINISH. Note that KVM_PRE_FAULT_MEMORY *before* KVM_SEV_SNP_LAUNCH_FINISH would not work, and is therefore explicitly blocked by the first patch in the series. The bulk of the changes are in patches 1, 7, 10 and 13. Everything else is small preparatory changes; many patches in the first half for example try to use struct folio more instead of struct page and pfns, which is useful when the code region before folio_unlock() is extended to the callers of kvm_gmem_get_folio(). There's also a couple cleanups in the middle, for example patches 4 and 8. Paolo Paolo Bonzini (14): KVM: x86: disallow pre-fault for SNP VMs before initialization KVM: guest_memfd: return folio from __kvm_gmem_get_pfn() KVM: guest_memfd: delay folio_mark_uptodate() until after successful preparation KVM: guest_memfd: do not go through struct page KVM: rename CONFIG_HAVE_KVM_GMEM_* to CONFIG_HAVE_KVM_ARCH_GMEM_* KVM: guest_memfd: return locked folio from __kvm_gmem_get_pfn KVM: guest_memfd: delay kvm_gmem_prepare_folio() until the memory is passed to the guest KVM: guest_memfd: make kvm_gmem_prepare_folio() operate on a single struct kvm KVM: remove kvm_arch_gmem_prepare_needed() KVM: guest_memfd: move check for already-populated page to common code KVM: cleanup and add shortcuts to kvm_range_has_memory_attributes() KVM: extend kvm_range_has_memory_attributes() to check subset of attributes KVM: guest_memfd: let kvm_gmem_populate() operate only on private gfns KVM: guest_memfd: abstract how prepared folios are recorded v1->v2: - patch 1: new - patch 7: point out benign race between page fault and hole-punch - patch 7: clean up comments - patch 10: clean up commit message - patch 11: remove ";;" - patch 13: fix length argument to kvm_range_has_memory_attributes() - patch 14: new Documentation/virt/kvm/api.rst | 6 + arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/Kconfig | 4 +- arch/x86/kvm/mmu/mmu.c | 5 +- arch/x86/kvm/svm/sev.c | 17 +-- arch/x86/kvm/svm/svm.c | 1 + arch/x86/kvm/x86.c | 12 +- include/linux/kvm_host.h | 9 +- virt/kvm/Kconfig | 4 +- virt/kvm/guest_memfd.c | 226 +++++++++++++++++++------------- virt/kvm/kvm_main.c | 73 +++++------ 11 files changed, 206 insertions(+), 152 deletions(-)