KVM: x86 emulator: during rep emulation decrement ECX only if emulation succeeded

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 8 insertions, 7 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 3b32270a20db..594574d8b9e9 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2411,13 +2411,13 @@ int emulator_task_switch(struct x86_emulate_ctxt *ctxt,
 }
 
 static void string_addr_inc(struct x86_emulate_ctxt *ctxt, unsigned long base,
-                            int reg, unsigned long **ptr)
+                            int reg, struct operand *op)
 {
         struct decode_cache *c = &ctxt->decode;
         int df = (ctxt->eflags & EFLG_DF) ? -1 : 1;
 
-        register_address_increment(c, &c->regs[reg], df * c->src.bytes);
-        *ptr = (unsigned long *)register_address(c,  base, c->regs[reg]);
+        register_address_increment(c, &c->regs[reg], df * op->bytes);
+        op->ptr = (unsigned long *)register_address(c,  base, c->regs[reg]);
 }
 
 int
@@ -2483,7 +2483,6 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
                                 goto done;
                         }
                 }
-                register_address_increment(c, &c->regs[VCPU_REGS_RCX], -1);
                 c->eip = ctxt->eip;
         }
 
@@ -2936,11 +2935,13 @@ writeback:
 
         if ((c->d & SrcMask) == SrcSI)
                 string_addr_inc(ctxt, seg_override_base(ctxt, c), VCPU_REGS_RSI,
-                                &c->src.ptr);
+                                &c->src);
 
         if ((c->d & DstMask) == DstDI)
-                string_addr_inc(ctxt, es_base(ctxt), VCPU_REGS_RDI,
-                                &c->dst.ptr);
+                string_addr_inc(ctxt, es_base(ctxt), VCPU_REGS_RDI, &c->dst);
+
+        if (c->rep_prefix && (c->d & String))
+                register_address_increment(c, &c->regs[VCPU_REGS_RCX], -1);
 
         /* Commit shadow register state. */
         memcpy(ctxt->vcpu->arch.regs, c->regs, sizeof c->regs);