The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 706c9c55e5a32800605eb6a864ef6e1ca0c6c179 Mon Sep 17 00:00:00 2001 From: Sean Christopherson seanjc@google.com Date: Sat, 23 Apr 2022 03:47:41 +0000 Subject: [PATCH] KVM: x86/mmu: Don't treat fully writable SPTEs as volatile (modulo A/D)

Don't treat SPTEs that are truly writable, i.e. writable in hardware, as being volatile (unless they're volatile for other reasons, e.g. A/D bits). KVM _sets_ the WRITABLE bit out of mmu_lock, but never _clears_ the bit out of mmu_lock, so if the WRITABLE bit is set, it cannot magically get cleared just because the SPTE is MMU-writable.

Rename the wrapper of MMU-writable to be more literal, the previous name of spte_can_locklessly_be_made_writable() is wrong and misleading.

Fixes: c7ba5b48cc8d ("KVM: MMU: fast path of handling guest page fault") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20220423034752.1161007-2-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 64a2a7e2be90..48dcb6a782f4 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -484,13 +484,15 @@ static bool spte_has_volatile_bits(u64 spte) * also, it can help us to get a stable is_writable_pte() * to ensure tlb flush is not missed. */ - if (spte_can_locklessly_be_made_writable(spte) || - is_access_track_spte(spte)) + if (!is_writable_pte(spte) && is_mmu_writable_spte(spte)) + return true; + + if (is_access_track_spte(spte)) return true;

if (spte_ad_enabled(spte)) { - if ((spte & shadow_accessed_mask) == 0 || - (is_writable_pte(spte) && (spte & shadow_dirty_mask) == 0)) + if (!(spte & shadow_accessed_mask) || + (is_writable_pte(spte) && !(spte & shadow_dirty_mask))) return true; }

@@ -557,7 +559,7 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte) * we always atomically update it, see the comments in * spte_has_volatile_bits(). */ - if (spte_can_locklessly_be_made_writable(old_spte) && + if (is_mmu_writable_spte(old_spte) && !is_writable_pte(new_spte)) flush = true;

@@ -1187,7 +1189,7 @@ static bool spte_write_protect(u64 *sptep, bool pt_protect) u64 spte = *sptep;

if (!is_writable_pte(spte) && - !(pt_protect && spte_can_locklessly_be_made_writable(spte))) + !(pt_protect && is_mmu_writable_spte(spte))) return false;

rmap_printk("spte %p %llx\n", sptep, *sptep); @@ -3196,8 +3198,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) * be removed in the fast path only if the SPTE was * write-protected for dirty-logging or access tracking. */ - if (fault->write && - spte_can_locklessly_be_made_writable(spte)) { + if (fault->write && is_mmu_writable_spte(spte)) { new_spte |= PT_WRITABLE_MASK;

/* diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h index e4abeb5df1b1..c571784cb567 100644 --- a/arch/x86/kvm/mmu/spte.h +++ b/arch/x86/kvm/mmu/spte.h @@ -390,7 +390,7 @@ static inline void check_spte_writable_invariants(u64 spte) "kvm: Writable SPTE is not MMU-writable: %llx", spte); }

-static inline bool spte_can_locklessly_be_made_writable(u64 spte) +static inline bool is_mmu_writable_spte(u64 spte) { return spte & shadow_mmu_writable_mask; }