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

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>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a7961f8a642936d0b9de214462349245c3dccecb..1e9c5ef4a9f588cf4263938cc9bd40a05c228244 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -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