diff options
| author | Sean Christopherson | 2019-09-12 19:46:03 -0700 |
|---|---|---|
| committer | Paolo Bonzini | 2019-09-24 14:35:12 +0200 |
| commit | fac026dac0bc4dc3bb2e72309fa47ff3c4dd7c16 (patch) | |
| tree | 1dae2382c2be3a8c91076151da2f8c0bcb4f8780 /arch/x86/kvm | |
| parent | d0f5a86a34072c46b7fe1b8f8768e666d9d6f87f (diff) | |
KVM: x86/mmu: Treat invalid shadow pages as obsolete
Treat invalid shadow pages as obsolete to fix a bug where an obsolete
and invalid page with a non-zero root count could become non-obsolete
due to mmu_valid_gen wrapping. The bug is largely theoretical with the
current code base, as an unsigned long will effectively never wrap on
64-bit KVM, and userspace would have to deliberately stall a vCPU in
order to keep an obsolete invalid page on the active list while
simultaneously modifying memslots billions of times to trigger a wrap.
The obvious alternative is to use a 64-bit value for mmu_valid_gen,
but it's actually desirable to go in the opposite direction, i.e. using
a smaller 8-bit value to reduce KVM's memory footprint by 8 bytes per
shadow page, and relying on proper treatment of invalid pages instead of
preventing the generation from wrapping.
Note, "Fixes" points at a commit that was at one point reverted, but has
since been restored.
Fixes: 5304b8d37c2a5 ("KVM: MMU: fast invalidate all pages")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm')
| -rw-r--r-- | arch/x86/kvm/mmu.c | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 84e1a9c661dd..151c4b94696f 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -2252,7 +2252,7 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm, #define for_each_valid_sp(_kvm, _sp, _gfn) \ hlist_for_each_entry(_sp, \ &(_kvm)->arch.mmu_page_hash[kvm_page_table_hashfn(_gfn)], hash_link) \ - if (is_obsolete_sp((_kvm), (_sp)) || (_sp)->role.invalid) { \ + if (is_obsolete_sp((_kvm), (_sp))) { \ } else #define for_each_gfn_indirect_valid_sp(_kvm, _sp, _gfn) \ @@ -2311,7 +2311,8 @@ static void mmu_audit_disable(void) { } static bool is_obsolete_sp(struct kvm *kvm, struct kvm_mmu_page *sp) { - return unlikely(sp->mmu_valid_gen != kvm->arch.mmu_valid_gen); + return sp->role.invalid || + unlikely(sp->mmu_valid_gen != kvm->arch.mmu_valid_gen); } static bool kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, |