Re: [Xen-devel] VM-exit instruction length and #GP fault on IN.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 27.01.15 at 06:48, <kevin.tian@xxxxxxxxx> wrote:
>>  From: Don Slutz [mailto:dslutz@xxxxxxxxxxx]
>> Sent: Tuesday, January 27, 2015 4:31 AM
>> 
>> The question is about the VM-exit instruction length field.
>> 
>> This is accessed in xen via:
>> 
>>    __vmread(VM_EXIT_INSTRUCTION_LEN, &inst_len);
>> 
>> an example of which is in routine get_instruction_length().
>> 
>> 
>> Is it architecturally defined that #GP intercept vmexits on IN and OUT
>> actually set this field?
>> 
>> What about other instructions?
> 
> I didn't catch the question here. There is no such a type called #GP
> intercept vmexit. That's why the behavior is documented per 
> instruction like you cited below.

That's EXIT_REASON_EXCEPTION_NMI with vector = TRAP_gp_fault.
The question is whether exception intercept VM exits set the
instruction length field for instructions where the respective instruction
based VM exit does so (in general, or at least for the specific case of
EXIT_REASON_IO_INSTRUCTION and an intercepted #GP).

Jan


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