* [PATCH v3] KVM: x86 emulator: fix REPZ/REPNZ termination condition
@ 2010-08-19 11:34 Avi Kivity
2010-08-19 12:09 ` Gleb Natapov
0 siblings, 1 reply; 3+ messages in thread
From: Avi Kivity @ 2010-08-19 11:34 UTC (permalink / raw)
To: Marcelo Tosatti, kvm, Gleb Natapov, Wei Yongjun
EFLAGS.ZF needs to be checked after each iteration, not before.
Signed-off-by: Avi Kivity <avi@redhat.com>
---
v3: if restarting an instruction, don't advance rip
arch/x86/kvm/emulate.c | 41 ++++++++++++++++++++---------------------
1 files changed, 20 insertions(+), 21 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 729853a..4372dc5 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2782,28 +2782,10 @@ 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)) {
@@ -3230,20 +3212,37 @@ 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;
--
1.7.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v3] KVM: x86 emulator: fix REPZ/REPNZ termination condition
2010-08-19 11:34 [PATCH v3] KVM: x86 emulator: fix REPZ/REPNZ termination condition Avi Kivity
@ 2010-08-19 12:09 ` Gleb Natapov
2010-08-19 12:14 ` Avi Kivity
0 siblings, 1 reply; 3+ messages in thread
From: Gleb Natapov @ 2010-08-19 12:09 UTC (permalink / raw)
To: Avi Kivity; +Cc: Marcelo Tosatti, kvm, Wei Yongjun
On Thu, Aug 19, 2010 at 02:34:08PM +0300, Avi Kivity wrote:
> EFLAGS.ZF needs to be checked after each iteration, not before.
>
> Signed-off-by: Avi Kivity <avi@redhat.com>
> ---
>
> v3: if restarting an instruction, don't advance rip
>
> arch/x86/kvm/emulate.c | 41 ++++++++++++++++++++---------------------
> 1 files changed, 20 insertions(+), 21 deletions(-)
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 729853a..4372dc5 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -2782,28 +2782,10 @@ 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)) {
> @@ -3230,20 +3212,37 @@ 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;
>
We will advance rip past instruction if exception is generated during
instruction emulation. Consequently exception will be injected at the
wrong rip. I think we should try different approach to fix this problem.
> done:
> return (rc == X86EMUL_UNHANDLEABLE) ? -1 : 0;
> --
> 1.7.1
--
Gleb.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v3] KVM: x86 emulator: fix REPZ/REPNZ termination condition
2010-08-19 12:09 ` Gleb Natapov
@ 2010-08-19 12:14 ` Avi Kivity
0 siblings, 0 replies; 3+ messages in thread
From: Avi Kivity @ 2010-08-19 12:14 UTC (permalink / raw)
To: Gleb Natapov; +Cc: Marcelo Tosatti, kvm, Wei Yongjun
On 08/19/2010 03:09 PM, Gleb Natapov wrote:
> On Thu, Aug 19, 2010 at 02:34:08PM +0300, Avi Kivity wrote:
>> EFLAGS.ZF needs to be checked after each iteration, not before.
>>
>> Signed-off-by: Avi Kivity<avi@redhat.com>
>> ---
>>
>> v3: if restarting an instruction, don't advance rip
>>
>> arch/x86/kvm/emulate.c | 41 ++++++++++++++++++++---------------------
>> 1 files changed, 20 insertions(+), 21 deletions(-)
>>
>> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
>> index 729853a..4372dc5 100644
>> --- a/arch/x86/kvm/emulate.c
>> +++ b/arch/x86/kvm/emulate.c
>> @@ -2782,28 +2782,10 @@ 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)) {
>> @@ -3230,20 +3212,37 @@ 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;
>>
> We will advance rip past instruction if exception is generated during
> instruction emulation. Consequently exception will be injected at the
> wrong rip. I think we should try different approach to fix this problem.
Yes, I agree. It's too confusing.
--
error compiling committee.c: too many arguments to function
^ permalink raw reply [flat|nested] 3+ messages in thread
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2010-08-19 11:34 [PATCH v3] KVM: x86 emulator: fix REPZ/REPNZ termination condition Avi Kivity
2010-08-19 12:09 ` Gleb Natapov
2010-08-19 12:14 ` Avi Kivity
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