KVM: x86 emulator: get rid of "restart" in emulation context.

x86_emulate_insn() will return 1 if instruction can be restarted
without re-entering a guest.
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/include/asm/kvm_emulate.h

@@ -224,7 +224,6 @@ struct x86_emulate_ctxt {
 	/* interruptibility state, as a result of execution of STI or MOV SS */
 	int interruptibility;
 
-	bool restart; /* restart string instruction after writeback */
 	bool perm_ok; /* do not check permissions if true */
 
 	int exception; /* exception that happens during emulation or -1 */
@@ -255,6 +254,9 @@ struct x86_emulate_ctxt {
 #endif
 
 int x86_decode_insn(struct x86_emulate_ctxt *ctxt);
+#define EMULATION_FAILED -1
+#define EMULATION_OK 0
+#define EMULATION_RESTART 1
 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

@@ -437,7 +437,6 @@ static void emulate_exception(struct x86_emulate_ctxt *ctxt, int vec,
 	ctxt->exception = vec;
 	ctxt->error_code = error;
 	ctxt->error_code_valid = valid;
-	ctxt->restart = false;
 }
 
 static void emulate_gp(struct x86_emulate_ctxt *ctxt, int err)
@@ -2633,9 +2632,6 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt)
 	struct opcode opcode, *g_mod012, *g_mod3;
 	struct operand memop = { .type = OP_NONE };
 
-	/* we cannot decode insn before we complete previous rep insn */
-	WARN_ON(ctxt->restart);
-
 	c->eip = ctxt->eip;
 	c->fetch.start = c->fetch.end = c->eip;
 	ctxt->cs_base = seg_base(ctxt, ops, VCPU_SREG_CS);
@@ -2985,10 +2981,8 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
 	}
 
 	if (c->rep_prefix && (c->d & String)) {
-		ctxt->restart = true;
 		/* All REP prefixes have the same first termination condition */
 		if (address_mask(c, c->regs[VCPU_REGS_RCX]) == 0) {
-			ctxt->restart = false;
 			ctxt->eip = c->eip;
 			goto done;
 		}
@@ -3446,28 +3440,29 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
 		struct read_cache *r = &ctxt->decode.io_read;
 		register_address_increment(c, &c->regs[VCPU_REGS_RCX], -1);
 
-		if (string_insn_completed(ctxt))
-			ctxt->restart = false;
+		if (!string_insn_completed(ctxt)) {
 			/*
-		 * Re-enter guest when pio read ahead buffer is empty or,
-		 * if it is not used, after each 1024 iteration.
+			 * Re-enter guest when pio read ahead buffer is empty
+			 * or, if it is not used, after each 1024 iteration.
 			 */
-		else if ((r->end == 0 && !(c->regs[VCPU_REGS_RCX] & 0x3ff)) ||
-			 (r->end != 0 && r->end == r->pos)) {
-			ctxt->restart = false;
-			c->eip = ctxt->eip;
-		}
-	}
+			if ((r->end != 0 || c->regs[VCPU_REGS_RCX] & 0x3ff) &&
+			    (r->end == 0 || r->end != r->pos)) {
 				/*
-	 * reset read cache here in case string instruction is restared
-	 * without decoding
+				 * Reset read cache. Usually happens before
+				 * decode, but since instruction is restarted
+				 * we have to do it here.
 				 */
 				ctxt->decode.mem_read.end = 0;
-	if (!ctxt->restart)
+				return EMULATION_RESTART;
+			}
+			goto done; /* skip rip writeback */
+		}
+	}
+
 	ctxt->eip = c->eip;
 
 done:
-	return (rc == X86EMUL_UNHANDLEABLE) ? -1 : 0;
+	return (rc == X86EMUL_UNHANDLEABLE) ? EMULATION_FAILED : EMULATION_OK;
 
 twobyte_insn:
 	switch (c->b) {

arch/x86/kvm/x86.c

@@ -4181,18 +4181,17 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
 restart:
 	r = x86_emulate_insn(&vcpu->arch.emulate_ctxt);
 
-	if (r) { /* emulation failed */
+	if (r == EMULATION_FAILED) {
 		if (reexecute_instruction(vcpu, cr2))
 			return EMULATE_DONE;
 
 		return handle_emulation_failure(vcpu);
 	}
 
-	r = EMULATE_DONE;
-
-	if (vcpu->arch.emulate_ctxt.exception >= 0)
+	if (vcpu->arch.emulate_ctxt.exception >= 0) {
 		inject_emulated_exception(vcpu);
-	else if (vcpu->arch.pio.count) {
+		r = EMULATE_DONE;
+	} else if (vcpu->arch.pio.count) {
 		if (!vcpu->arch.pio.in)
 			vcpu->arch.pio.count = 0;
 		r = EMULATE_DO_MMIO;
@@ -4200,8 +4199,10 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
 		if (vcpu->mmio_is_write)
 			vcpu->mmio_needed = 0;
 		r = EMULATE_DO_MMIO;
-	} else if (vcpu->arch.emulate_ctxt.restart)
+	} else if (r == EMULATION_RESTART)
 		goto restart;
+	else
+		r = EMULATE_DONE;
 
 	toggle_interruptibility(vcpu, vcpu->arch.emulate_ctxt.interruptibility);
 	kvm_x86_ops->set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);
@@ -5100,8 +5101,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	if (!irqchip_in_kernel(vcpu->kvm))
 		kvm_set_cr8(vcpu, kvm_run->cr8);
 
-	if (vcpu->arch.pio.count || vcpu->mmio_needed ||
-	    vcpu->arch.emulate_ctxt.restart) {
+	if (vcpu->arch.pio.count || vcpu->mmio_needed) {
 		if (vcpu->mmio_needed) {
 			memcpy(vcpu->mmio_data, kvm_run->mmio.data, 8);
 			vcpu->mmio_read_completed = 1;