> On Jun 9, 2020, at 18:54, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
>
> No need to resend, the patch is good. Here is my take on the commit message:
Thank you Paolo! Your commit message is much clearer.
I really appreciate your great job.
Best
Eiichi
>
> Commit b1394e745b94 ("KVM: x86: fix APIC page invalidation") tried
> to fix inappropriate APIC page invalidation by re-introducing arch
> specific kvm_arch_mmu_notifier_invalidate_range() and calling it from
> kvm_mmu_notifier_invalidate_range_start. However, the patch left a
> possible race where the VMCS APIC address cache is updated *before*
> it is unmapped:
>
> (Invalidator) kvm_mmu_notifier_invalidate_range_start()
> (Invalidator) kvm_make_all_cpus_request(kvm, KVM_REQ_APIC_PAGE_RELOAD)
> (KVM VCPU) vcpu_enter_guest()
> (KVM VCPU) kvm_vcpu_reload_apic_access_page()
> (Invalidator) actually unmap page
>
> Because of the above race, there can be a mismatch between the
> host physical address stored in the APIC_ACCESS_PAGE VMCS field and
> the host physical address stored in the EPT entry for the APIC GPA
> (0xfee0000). When this happens, the processor will not trap APIC
> accesses, and will instead show the raw contents of the APIC-access page.
> Because Windows OS periodically checks for unexpected modifications to
> the LAPIC register, this will show up as a BSOD crash with BugCheck
> CRITICAL_STRUCTURE_CORRUPTION (109) we are currently seeing in
> https://urldefense.proofpoint.com/v2/url?u=https-3A__bugzilla.redhat.com_show-5Fbug.cgi-3Fid-3D1751017&d=DwIDaQ&c=s883GpUCOChKOHiocYtGcg&r=dy01Dr4Ly8mhvnUdx1pZhhT1bkq4h9z5aVWu3paoZtk&m=yo6pYK4bnrvDLz_RwGyvwtJEY6oWkg-9XGlbPBq1B2g&s=7tKkV92x4mCNLQ7miJIanMVqokYNJdjrcK4Rqqb_h7s&e= .
>
> The root cause of the issue is that kvm_arch_mmu_notifier_invalidate_range()
> cannot guarantee that no additional references are taken to the pages in
> the range before kvm_mmu_notifier_invalidate_range_end(). Fortunately,
> this case is supported by the MMU notifier API, as documented in
> include/linux/mmu_notifier.h:
>
> * If the subsystem
> * can't guarantee that no additional references are taken to
> * the pages in the range, it has to implement the
> * invalidate_range() notifier to remove any references taken
> * after invalidate_range_start().
>
> The fix therefore is to reload the APIC-access page field in the VMCS
> from kvm_mmu_notifier_invalidate_range() instead of ..._range_start().
>
> Thanks,
>
> Paolo
