[PATCH 1/2] KVM: Exception during emulation decode should propagate

[Nadav Amit]

An exception might occur during decode (e.g., #PF during fetch).
Currently, the exception is ignored and emulation is performed.
Instead, emulation should be skipped and the fault should be injected.
Skipping instruction should report a failure in this case.

Signed-off-by: Nadav Amit <nadav.amit@xxxxxxxxx>
---
 arch/x86/kvm/emulate.c |    3 +++
 arch/x86/kvm/x86.c     |    8 ++++++++
 2 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 05a562b..e06dc98 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3869,6 +3869,9 @@ done:
 	if (ctxt->memopp && ctxt->memopp->type == OP_MEM && ctxt->rip_relative)
 		ctxt->memopp->addr.mem.ea += ctxt->_eip;
 
+	if (rc == X86EMUL_PROPAGATE_FAULT)
+		ctxt->have_exception = true;
+
 	return (rc != X86EMUL_CONTINUE) ? EMULATION_FAILED : EMULATION_OK;
 }
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1171def..05fd3d7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4443,10 +4443,17 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 	}
 
 	if (emulation_type & EMULTYPE_SKIP) {
+		if (ctxt->have_exception)
+			return EMULATE_FAIL;
 		kvm_rip_write(vcpu, ctxt->_eip);
 		return EMULATE_DONE;
 	}
 
+	if (ctxt->have_exception) {
+		writeback = false;
+		goto post;
+	}
+
 	if (retry_instruction(ctxt, cr2, emulation_type))
 		return EMULATE_DONE;
 
@@ -4470,6 +4477,7 @@ restart:
 		return handle_emulation_failure(vcpu);
 	}
 
+post:
 	if (ctxt->have_exception) {
 		inject_emulated_exception(vcpu);
 		r = EMULATE_DONE;
-- 
1.7.4.1

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