[PATCH v3 1/2] KVM: x86/mmu: Skip mmu_notifier check when handling MMIO page fault

[David Stevens]

From: Sean Christopherson <seanjc at google.com>

Don't retry a page fault due to an mmu_notifier invalidation when
handling a page fault for a GPA that did not resolve to a memslot, i.e.
an MMIO page fault.  Invalidations from the mmu_notifier signal a change
in a host virtual address (HVA) mapping; without a memslot, there is no
HVA and thus no possibility that the invalidation is relevant to the
page fault being handled.

Note, the MMIO vs. memslot generation checks handle the case where a
pending memslot will create a memslot overlapping the faulting GPA.  The
mmu_notifier checks are orthogonal to memslot updates.

Signed-off-by: Sean Christopherson <seanjc at google.com>
---
 arch/x86/kvm/mmu/mmu.c         | 2 +-
 arch/x86/kvm/mmu/paging_tmpl.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6d16481aa29d..9ac0a727015d 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3725,7 +3725,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
 
 	r = RET_PF_RETRY;
 	spin_lock(&vcpu->kvm->mmu_lock);
-	if (mmu_notifier_retry(vcpu->kvm, mmu_seq))
+	if (!is_noslot_pfn(pfn) && mmu_notifier_retry(vcpu->kvm, mmu_seq))
 		goto out_unlock;
 	r = make_mmu_pages_available(vcpu);
 	if (r)
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 50e268eb8e1a..ab54263d857c 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -869,7 +869,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
 
 	r = RET_PF_RETRY;
 	spin_lock(&vcpu->kvm->mmu_lock);
-	if (mmu_notifier_retry(vcpu->kvm, mmu_seq))
+	if (!is_noslot_pfn(pfn) && mmu_notifier_retry(vcpu->kvm, mmu_seq))
 		goto out_unlock;
 
 	kvm_mmu_audit(vcpu, AUDIT_PRE_PAGE_FAULT);
-- 
2.30.0.280.ga3ce27912f-goog