KVM: x86: skip writeback on injection of nested exception

If a nested page fault happens during emulation, we will inject a vmexit,
not a page fault.  However because writeback happens after the injection,
we will write ctxt->eip from L2 into the L1 EIP.  We do not write back
if an instruction caused an interception vmexit---do the same for page
faults.

Suggested-by: Gleb Natapov <gleb@kernel.org>
Reviewed-by: Gleb Natapov <gleb@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 10 insertions, 6 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 08cc299ec6f4..c9896518e54d 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -893,7 +893,6 @@ void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault);
 int kvm_read_guest_page_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
                             gfn_t gfn, void *data, int offset, int len,
                             u32 access);
-void kvm_propagate_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault);
 bool kvm_require_cpl(struct kvm_vcpu *vcpu, int required_cpl);
 
 static inline int __kvm_irq_line_state(unsigned long *irq_state,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e4ed85e07a01..354194671902 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -408,12 +408,14 @@ void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault)
 }
 EXPORT_SYMBOL_GPL(kvm_inject_page_fault);
 
-void kvm_propagate_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault)
+static bool kvm_propagate_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault)
 {
         if (mmu_is_nested(vcpu) && !fault->nested_page_fault)
                 vcpu->arch.nested_mmu.inject_page_fault(vcpu, fault);
         else
                 vcpu->arch.mmu.inject_page_fault(vcpu, fault);
+
+        return fault->nested_page_fault;
 }
 
 void kvm_inject_nmi(struct kvm_vcpu *vcpu)
@@ -4929,16 +4931,18 @@ static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)
         }
 }
 
-static void inject_emulated_exception(struct kvm_vcpu *vcpu)
+static bool inject_emulated_exception(struct kvm_vcpu *vcpu)
 {
         struct x86_emulate_ctxt *ctxt = &vcpu->arch.emulate_ctxt;
         if (ctxt->exception.vector == PF_VECTOR)
-                kvm_propagate_fault(vcpu, &ctxt->exception);
-        else if (ctxt->exception.error_code_valid)
+                return kvm_propagate_fault(vcpu, &ctxt->exception);
+
+        if (ctxt->exception.error_code_valid)
                 kvm_queue_exception_e(vcpu, ctxt->exception.vector,
                                       ctxt->exception.error_code);
         else
                 kvm_queue_exception(vcpu, ctxt->exception.vector);
+        return false;
 }
 
 static void init_emulate_ctxt(struct kvm_vcpu *vcpu)
@@ -5300,8 +5304,9 @@ restart:
         }
 
         if (ctxt->have_exception) {
-                inject_emulated_exception(vcpu);
                 r = EMULATE_DONE;
+                if (inject_emulated_exception(vcpu))
+                        return r;
         } else if (vcpu->arch.pio.count) {
                 if (!vcpu->arch.pio.in) {
                         /* FIXME: return into emulator if single-stepping.  */