On 8/9/24 21:03, Sean Christopherson wrote:
Drop the manual pfn look when retrying an instruction that KVM failed to
emulation in response to a #PF due to a write-protected gfn. Now that KVM
sets EMULTYPE_PF if and only if the page fault it a write-protected gfn,
Pointing out where this happened will likely help a few years from now:
With the introduction of RET_PF_WRITE_PROTECTED, KVM sets EMULTYPE_PF if
and only if the page fault it a write-protected gfn, i.e. if and only if
there's a writable memslot. KVM will never try to redo an instruction
that failed on emulated MMIO (no slot, or a write to a read-only slot),
so therefore there's no redo the lookup in reexecute_instruction().
Paolo
i.e. if and only if there's a writable memslot, there's no need to redo
the lookup to avoid retrying an instruction that failed on emulated MMIO
(no slot, or a write to a read-only slot).
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 18 ------------------
1 file changed, 18 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 771e67381fce..67f9871990fb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8867,7 +8867,6 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
int emulation_type)
{
gpa_t gpa = cr2_or_gpa;
- kvm_pfn_t pfn;
if (!(emulation_type & EMULTYPE_ALLOW_RETRY_PF))
return false;
@@ -8887,23 +8886,6 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
return true;
}
- /*
- * Do not retry the unhandleable instruction if it faults on the
- * readonly host memory, otherwise it will goto a infinite loop:
- * retry instruction -> write #PF -> emulation fail -> retry
- * instruction -> ...
- */
- pfn = gfn_to_pfn(vcpu->kvm, gpa_to_gfn(gpa));
-
- /*
- * If the instruction failed on the error pfn, it can not be fixed,
- * report the error to userspace.
- */
- if (is_error_noslot_pfn(pfn))
- return false;
-
- kvm_release_pfn_clean(pfn);
-
/*
* If emulation may have been triggered by a write to a shadowed page
* table, unprotect the gfn (zap any relevant SPTEs) and re-enter the
