On Tue, Aug 17, 2010 at 11:26:43AM +0300, Avi Kivity wrote:
> EFLAGS.ZF needs to be checked after each iteration, not before.
>
> Signed-off-by: Avi Kivity <[email protected]>
> ---
> arch/x86/kvm/emulate.c | 42 +++++++++++++++++++++++-------------------
> 1 files changed, 23 insertions(+), 19 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 0c0ada9..a2edfb1 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -2747,6 +2747,7 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
> int rc = X86EMUL_CONTINUE;
> int saved_dst_type = c->dst.type;
> int irq; /* Used for int 3, int, and into */
> + ulong old_eip;
Is never used.
>
> ctxt->decode.mem_read.pos = 0;
>
> @@ -2771,28 +2772,10 @@ 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) {
> @@ -3229,6 +3212,7 @@ special_insn:
> }
>
> writeback:
> + old_eip = c->eip;
> rc = writeback(ctxt, ops);
> if (rc != X86EMUL_CONTINUE)
> goto done;
> @@ -3250,13 +3234,33 @@ 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)) {
> + trace_printk("c->eip %lx ctxt->eip %lx\n",
> + c->eip, ctxt->eip);
> + if (((c->rep_prefix == REPE_PREFIX) &&
> + ((ctxt->eflags & EFLG_ZF) == 0))
> + || ((c->rep_prefix == REPNE_PREFIX) &&
> + ((ctxt->eflags & EFLG_ZF) == EFLG_ZF))) {
> + ctxt->restart = false;
Why not jump to string_done label here?
> + }
> + }
> /*
> * 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))
> + (rc->end != 0 && rc->end == rc->pos)) {
> ctxt->restart = false;
> + c->eip = ctxt->eip;
We can get here when instruction is completed by above "if", so same
instruction will reexecute once again.
> + }
> }
> /*
> * reset read cache here in case string instruction is restared
> --
> 1.7.1
>
> --
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--
Gleb.
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