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KVM: x86: Remove manual pfn lookup when retrying #PF after failed emulation

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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_ALLOW_RETRY_PF if and only if the page fault hit a write-
protected gfn, 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).

I.e. KVM will never attempt to retry an instruction that failed on
emulated MMIO, whereas that was not the case prior to the introduction of
RET_PF_WRITE_PROTECTED.

Reviewed-by: Yuan Yao <yuan.yao@intel.com>
Link: https://lore.kernel.org/r/20240831001538.336683-16-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2024-08-30 17:15:30 -07:00
parent b299c273c0
commit 6205257395
1 changed files with 0 additions and 18 deletions
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18
arch/x86/kvm/x86.c
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@ -8865,7 +8865,6 @@ 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;
@ -8885,23 +8884,6 @@ 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