Don't bother unprotecting the target gfn if EMULTYPE_WRITE_PF_TO_SP is
set, as KVM will simply report the emulation failure to userspace. This
will allow converting reexecute_instruction() to use
kvm_mmu_unprotect_gfn_instead_retry() instead of kvm_mmu_unprotect_page().
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 28 +++++++++++++++++++---------
1 file changed, 19 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 67f9871990fb..bbb63cf9fe2c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8871,6 +8871,19 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
if (!(emulation_type & EMULTYPE_ALLOW_RETRY_PF))
return false;
+ /*
+ * If the failed instruction faulted on an access to page tables that
+ * are used to translate any part of the instruction, KVM can't resolve
+ * the issue by unprotecting the gfn, as zapping the shadow page will
+ * result in the instruction taking a !PRESENT page fault and thus put
+ * the vCPU into an infinite loop of page faults. E.g. KVM will create
+ * a SPTE and write-protect the gfn to resolve the !PRESENT fault, and
+ * then zap the SPTE to unprotect the gfn, and then do it all over
+ * again. Report the error to userspace.
+ */
+ if (emulation_type & EMULTYPE_WRITE_PF_TO_SP)
+ return false;
+
if (!vcpu->arch.mmu->root_role.direct) {
/*
* Write permission should be allowed since only
@@ -8896,16 +8909,13 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(gpa));
/*
- * If the failed instruction faulted on an access to page tables that
- * are used to translate any part of the instruction, KVM can't resolve
- * the issue by unprotecting the gfn, as zapping the shadow page will
- * result in the instruction taking a !PRESENT page fault and thus put
- * the vCPU into an infinite loop of page faults. E.g. KVM will create
- * a SPTE and write-protect the gfn to resolve the !PRESENT fault, and
- * then zap the SPTE to unprotect the gfn, and then do it all over
- * again. Report the error to userspace.
+ * Retry even if _this_ vCPU didn't unprotect the gfn, as it's possible
+ * all SPTEs were already zapped by a different task. The alternative
+ * is to report the error to userspace and likely terminate the guest,
+ * and the infinite loop detection logic will prevent retrying the page
+ * fault indefinitely, i.e. there's nothing to lose by retrying.
*/
- return !(emulation_type & EMULTYPE_WRITE_PF_TO_SP);
+ return true;
}
static int complete_emulated_mmio(struct kvm_vcpu *vcpu);
--
2.46.0.76.ge559c4bf1a-goog
