3 files changed, 30 insertions, 33 deletions

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index 1bbf2b6f2a7e..1bf11400ae99 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/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,
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 3dcbc1d0a59d..ec35a71d8b5d 100644
--- a/arch/x86/kvm/emulate.c
+++ b/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 @@ writeback:
                 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;
-                /*
-                 * 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 (!string_insn_completed(ctxt)) {
+                        /*
+                         * Re-enter guest when pio read ahead buffer is empty
+                         * or, if it is not used, after each 1024 iteration.
+                         */
+                        if ((r->end != 0 || c->regs[VCPU_REGS_RCX] & 0x3ff) &&
+                            (r->end == 0 || r->end != r->pos)) {
+                                /*
+                                 * Reset read cache. Usually happens before
+                                 * decode, but since instruction is restarted
+                                 * we have to do it here.
+                                 */
+                                ctxt->decode.mem_read.end = 0;
+                                return EMULATION_RESTART;
+                        }
+                        goto done; /* skip rip writeback */
                 }
         }
-        /*
-         * reset read cache here in case string instruction is restared
-         * without decoding
-         */
-        ctxt->decode.mem_read.end = 0;
-        if (!ctxt->restart)
-                ctxt->eip = c->eip;
+
+        ctxt->eip = c->eip;
 
 done:
-        return (rc == X86EMUL_UNHANDLEABLE) ? -1 : 0;
+        return (rc == X86EMUL_UNHANDLEABLE) ? EMULATION_FAILED : EMULATION_OK;
 
 twobyte_insn:
         switch (c->b) {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d4d33f943d99..bc96ac9ed912 100644
--- a/arch/x86/kvm/x86.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 @@ restart:
                 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;