KVM: x86 emulator: fix REPZ/REPNZ termination condition

EFLAGS.ZF needs to be checked after each iteration, not before.

Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 09c9210..aab62d5 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2781,28 +2781,10 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
                ctxt->restart = true;
                /* All REP prefixes have the same first termination condition */
                if (address_mask(c, c->regs[VCPU_REGS_RCX]) == 0) {
-               string_done:
                        ctxt->restart = false;
                        ctxt->eip = c->eip;
                        goto done;
                }
-               /* The second termination condition only applies for REPE
-                * and REPNE. Test if the repeat string operation prefix is
-                * REPE/REPZ or REPNE/REPNZ and if it's the case it tests the
-                * corresponding termination condition according to:
-                *      - if REPE/REPZ and ZF = 0 then done
-                *      - if REPNE/REPNZ and ZF = 1 then done
-                */
-               if ((c->b == 0xa6) || (c->b == 0xa7) ||
-                   (c->b == 0xae) || (c->b == 0xaf)) {
-                       if ((c->rep_prefix == REPE_PREFIX) &&
-                           ((ctxt->eflags & EFLG_ZF) == 0))
-                               goto string_done;
-                       if ((c->rep_prefix == REPNE_PREFIX) &&
-                           ((ctxt->eflags & EFLG_ZF) == EFLG_ZF))
-                               goto string_done;
-               }
-               c->eip = ctxt->eip;
        }
 
        if ((c->src.type == OP_MEM) && !(c->d & NoAccess)) {
@@ -3229,20 +3211,37 @@ writeback:
        if (c->rep_prefix && (c->d & String)) {
                struct read_cache *rc = &ctxt->decode.io_read;
                register_address_increment(c, &c->regs[VCPU_REGS_RCX], -1);
+               /* The second termination condition only applies for REPE
+                * and REPNE. Test if the repeat string operation prefix is
+                * REPE/REPZ or REPNE/REPNZ and if it's the case it tests the
+                * corresponding termination condition according to:
+                *      - if REPE/REPZ and ZF = 0 then done
+                *      - if REPNE/REPNZ and ZF = 1 then done
+                */
+               if (((c->b == 0xa6) || (c->b == 0xa7) ||
+                    (c->b == 0xae) || (c->b == 0xaf))
+                   && (((c->rep_prefix == REPE_PREFIX) &&
+                        ((ctxt->eflags & EFLG_ZF) == 0))
+                       || ((c->rep_prefix == REPNE_PREFIX) &&
+                           ((ctxt->eflags & EFLG_ZF) == EFLG_ZF))))
+                       ctxt->restart = false;
                /*
                 * Re-enter guest when pio read ahead buffer is empty or,
                 * if it is not used, after each 1024 iteration.
                 */
-               if ((rc->end == 0 && !(c->regs[VCPU_REGS_RCX] & 0x3ff)) ||
-                   (rc->end != 0 && rc->end == rc->pos))
+               else if ((rc->end == 0 && !(c->regs[VCPU_REGS_RCX] & 0x3ff)) ||
+                        (rc->end != 0 && rc->end == rc->pos)) {
                        ctxt->restart = false;
+                       c->eip = ctxt->eip;
+               }
        }
        /*
         * reset read cache here in case string instruction is restared
         * without decoding
         */
        ctxt->decode.mem_read.end = 0;
-       ctxt->eip = c->eip;
+       if (!ctxt->restart)
+               ctxt->eip = c->eip;
 
 done:
        return (rc == X86EMUL_UNHANDLEABLE) ? -1 : 0;