Effectively force kvm_mmu_page_fault() to opt-in to allowing retry to
make it more obvious when and why it allows emulation to be retried.
Previously this approach was less convenient due to retry and
re-execute behavior being controlled by separate flags that were also
inverted in their implementations (opt-in versus opt-out).
Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
arch/x86/kvm/mmu.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 0246a1ea7f55..01fb8701ccd0 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5217,7 +5217,7 @@ static int make_mmu_pages_available(struct kvm_vcpu *vcpu)
int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code,
void *insn, int insn_len)
{
- int r, emulation_type = EMULTYPE_ALLOW_RETRY;
+ int r, emulation_type = 0;
enum emulation_result er;
bool direct = vcpu->arch.mmu.direct_map;
@@ -5230,10 +5230,8 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code,
r = RET_PF_INVALID;
if (unlikely(error_code & PFERR_RSVD_MASK)) {
r = handle_mmio_page_fault(vcpu, cr2, direct);
- if (r == RET_PF_EMULATE) {
- emulation_type = 0;
+ if (r == RET_PF_EMULATE)
goto emulate;
- }
}
if (r == RET_PF_INVALID) {
@@ -5260,8 +5258,16 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code,
return 1;
}
- if (mmio_info_in_cache(vcpu, cr2, direct))
- emulation_type = 0;
+ /*
+ * vcpu->arch.mmu.page_fault returned RET_PF_EMULATE, but we can still
+ * optimistically try to just unprotect the page and let the processor
+ * re-execute the instruction that caused the page fault. Do not allow
+ * retrying MMIO emulation, as it's not only pointless but could also
+ * cause us to enter an infinite loop because the processor will keep
+ * faulting on the non-existent MMIO address.
+ */
+ if (!mmio_info_in_cache(vcpu, cr2, direct))
+ emulation_type = EMULTYPE_ALLOW_RETRY;
emulate:
/*
* On AMD platforms, under certain conditions insn_len may be zero on #NPF.
--
2.18.0
