| Message ID | 20220217053028.96432-1-leobras@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | x86/kvm/fpu: Fix guest migration bugs that can crash guest | expand |
On 2/17/22 06:30, Leonardo Bras wrote: > This patchset comes from a bug I found during qemu guest migration from a > host with newer CPU to a host with an older version of this CPU, and thus > having less FPU features. > > When the guests were created, the one with less features is used as > config, so migration is possible. > > Patch 1 fix a bug that always happens during this migration, and is > related to the fact that xsave saves all feature flags, but xrstor does > not touch the PKRU flag. It also changes how fpstate->user_xfeatures > is set, going from kvm_check_cpuid() to the later called > kvm_vcpu_after_set_cpuid(). > > Patch 2 removes kvm_vcpu_arch.guest_supported_xcr0 since it now > duplicates guest_fpu.fpstate->user_xfeatures. Some wrappers were > introduced in order to make it easier to read the replaced version. > > Patches were compile-tested, and could fix the bug found. Queued, thanks (for 5.17 of course)! For patch 2, I renamed the function to kvm_guest_supported_xcr0. Paolo > Please let me know of anything to improve! > > Best regards, > Leo > > -- > Changes since v3: > - Add new patch to remove the use of kvm_vcpu_arch.guest_supported_xcr0, > since it is now duplicating guest_fpu.fpstate->user_xfeatures. > - On patch 1, also avoid setting user_xfeatures on kvm_check_cpuid(), > since it is already set in kvm_vcpu_after_set_cpuid() now. > Changes since v2: > - Fix building error because I forgot to EXPORT_SYMBOL(fpu_user_cfg) > Changes since v1: > - Instead of masking xfeatures, mask user_xfeatures instead. This will > only change the value sent to user, instead of the one saved in buf. > - Above change removed the need of the patch 2/2 > - Instead of masking the current value of user_xfeatures, save on it > fpu_user_cfg.default_features & vcpu->arch.guest_supported_xcr0 > > Leonardo Bras (2): > x86/kvm/fpu: Mask guest fpstate->xfeatures with guest_supported_xcr0 > x86/kvm/fpu: Remove kvm_vcpu_arch.guest_supported_xcr0 > > arch/x86/include/asm/kvm_host.h | 1 - > arch/x86/kernel/fpu/xstate.c | 5 ++++- > arch/x86/kvm/cpuid.c | 5 ++++- > arch/x86/kvm/x86.c | 20 +++++++++++++++----- > 4 files changed, 23 insertions(+), 8 deletions(-) >
On Thu, Feb 17, 2022 at 11:52 AM Paolo Bonzini <pbonzini@redhat.com> wrote: > > On 2/17/22 06:30, Leonardo Bras wrote: > > This patchset comes from a bug I found during qemu guest migration from a > > host with newer CPU to a host with an older version of this CPU, and thus > > having less FPU features. > > > > When the guests were created, the one with less features is used as > > config, so migration is possible. > > > > Patch 1 fix a bug that always happens during this migration, and is > > related to the fact that xsave saves all feature flags, but xrstor does > > not touch the PKRU flag. It also changes how fpstate->user_xfeatures > > is set, going from kvm_check_cpuid() to the later called > > kvm_vcpu_after_set_cpuid(). > > > > Patch 2 removes kvm_vcpu_arch.guest_supported_xcr0 since it now > > duplicates guest_fpu.fpstate->user_xfeatures. Some wrappers were > > introduced in order to make it easier to read the replaced version. > > > > Patches were compile-tested, and could fix the bug found. > > Queued, thanks (for 5.17 of course)! For patch 2, I renamed the > function to kvm_guest_supported_xcr0. > > Paolo > That's great! Thanks Paolo!