Re: [Xen-devel] [PATCH 09/10] tools/x86emul: Advertise more CPUID features for testing purposes

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 27.03.17 at 13:20, <george.dunlap@xxxxxxxxxx> wrote:
> On 27/03/17 10:56, Andrew Cooper wrote:
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
>> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
>> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
>> ---
>>  tools/tests/x86_emulator/x86_emulate.c | 41 
>> ++++++++++++++++++++++++----------
>>  1 file changed, 29 insertions(+), 12 deletions(-)
>> 
>> diff --git a/tools/tests/x86_emulator/x86_emulate.c 
> b/tools/tests/x86_emulator/x86_emulate.c
>> index cea0595..2c49954 100644
>> --- a/tools/tests/x86_emulator/x86_emulate.c
>> +++ b/tools/tests/x86_emulator/x86_emulate.c
>> @@ -73,20 +73,37 @@ int emul_test_cpuid(
>>           : "a" (leaf), "c" (subleaf));
>>  Oh, s
>>      /*
>> -     * The emulator doesn't itself use MOVBE, so we can always run the
>> -     * respective tests.
>> +     * Some instructions and features can be emulated without specific
>> +     * hardware support.  These features are unconditionally reported here,
>> +     * for testing and fuzzing-coverage purposes.
> 
> But similarly to my question in patch 10 -- is there any chance that the
> emulator will ever be called with a cpuid callback that returns 'false"
> for these?  If so, isn't there therefore a chance that there will be
> some sort of bug which only triggers if these bits are set to 'false'?

I think I've suggested before that the cpuid hook should actually
return void, as it can't possibly fail (now that CPUID faulting is
being handled in generic code).

Jan


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