Re: [PATCH] Correct management of REP prefix

[Laurent Vivier <Laurent.Vivier-6ktuUTfB/bM@public.gmane.org>]

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Avi Kivity wrote:
> Laurent Vivier wrote:
>> This patch corrects some errors appearing when we have an emulation
>> failure
>> on an operation using REP prefix.
>>
>> When x86_emulate_insn() fails, saving EIP and ECX is not enough as
>> emulation
>> should have modified other registers like RSI or RDI. Moreover, the
>> emulation
>> can fail on the writeback, and in this case we are not able to restore
>> registers.
>>
>> This patch takes another approach: at the beginning of
>> x86_emulate_insn() we restore state we have at end of
>> x86_decode_insn(). To do that, we store EIP in
>> a new field in decode_cache, decode_eip. This field store the EIP as
>> it is at
>> the end of x86_decode_insn(); and at beginning of x86_emulate_insn(),
>> we restore
>> all registers as they are in vcpu. We can do that, because the
>> x86_decode_insn()
>> doesn't modify registers (except EIP).
>>   
> 
> How about doing it slightly differently: keep c->eip at its current
> meaning, and add c->eip_orig to revert to? That will make the patch
> smaller and reduce the changes of something being missed.

I didn't do like that because I was afraid to miss some points to restore orig_eip.

But a patch will follow...

Laurent
-- 
------------- Laurent.Vivier-6ktuUTfB/bM@public.gmane.org  --------------
          "Software is hard" - Donald Knuth


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