KVM: x86 emulator: Don't write-back cpu-state on X86EMUL_INTERCEPTED

This patch prevents the changed CPU state to be written back
when the emulator detected that the instruction was
intercepted by the guest.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/include/asm/kvm_emulate.h

@@ -331,6 +331,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len);
 #define EMULATION_FAILED -1
 #define EMULATION_OK 0
 #define EMULATION_RESTART 1
+#define EMULATION_INTERCEPTED 2
 int x86_emulate_insn(struct x86_emulate_ctxt *ctxt);
 int emulator_task_switch(struct x86_emulate_ctxt *ctxt,
 			 u16 tss_selector, int reason,

arch/x86/kvm/emulate.c

@@ -3592,6 +3592,9 @@ writeback:
 done:
 	if (rc == X86EMUL_PROPAGATE_FAULT)
 		ctxt->have_exception = true;
+	if (rc == X86EMUL_INTERCEPTED)
+		return EMULATION_INTERCEPTED;
+
 	return (rc == X86EMUL_UNHANDLEABLE) ? EMULATION_FAILED : EMULATION_OK;
 
 twobyte_insn:

arch/x86/kvm/x86.c

@@ -4516,6 +4516,9 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 restart:
 	r = x86_emulate_insn(&vcpu->arch.emulate_ctxt);
 
+	if (r == EMULATION_INTERCEPTED)
+		return EMULATE_DONE;
+
 	if (r == EMULATION_FAILED) {
 		if (reexecute_instruction(vcpu, cr2))
 			return EMULATE_DONE;