Re: [PATCH 2/2] Provide fast path for "rep ins" emulation if possible.

[Avi Kivity <avi@redhat.com>]

On 05/23/2012 05:40 PM, Avi Kivity wrote:
> On 05/23/2012 05:08 PM, Gleb Natapov wrote:
>> "rep ins" emulation is going through emulator now. This is slow because
>> emulator knows how to write back only one datum at a time. This patch
>> provides fast path for the instruction in certain conditions. The
>> conditions are: DF flag is not set, destination memory is RAM and single
>> datum does not cross page boundary. If fast path code fails it falls
>> back to emulation.
>> 
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index f75af40..20e3fb0 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -1887,21 +1887,31 @@ static int io_interception(struct vcpu_svm *svm)
>>  {
>>  	struct kvm_vcpu *vcpu = &svm->vcpu;
>>  	u32 io_info = svm->vmcb->control.exit_info_1; /* address size bug? */
>> -	int size, in, string;
>> +	int size, in, string, rep;
>>  	unsigned port;
>>  
>>  	++svm->vcpu.stat.io_exits;
>>  	string = (io_info & SVM_IOIO_STR_MASK) != 0;
>> +	rep = (io_info & SVM_IOIO_REP_MASK) != 0;
>>  	in = (io_info & SVM_IOIO_TYPE_MASK) != 0;
>> -	if (string || in)
>> -		return emulate_instruction(vcpu, 0) == EMULATE_DONE;
>>  
> 
> If decode assists are not available, we still need to emulate, see 15.33.5.
> 

Joerg, the 2010 version of the manual says that the effective segment
(10:12) is only available with decode assists.  The 2012 version says
it's unconditional. What's correct?

-- 
error compiling committee.c: too many arguments to function