Re: [PATCH 1/4] x86 paravirt_ops: create no_paravirt.h for native ops

Jeremy Fitzhardinge
2006-08-07T05:43:43Z

Andi Kleen wrote:
>> +/* Stop speculative execution */
>> +static inline void sync_core(void)
>> +{
>> + unsigned int eax = 1, ebx, ecx, edx;
>> + __cpuid(&eax, &ebx, &ecx, &edx);
>> +}
>>
>
> Actually I don't think this one should be para virtualized at all.
> I don't see any reason at all why a hypervisor should trap it and it
> is very time critical. I would recommend you move it back into the
> normal files without hooks.
>

When VT/AMDV is enabled, cpuid could cause a vm exit, so it would be
nice to use one of the other serializing instructions in this case. For
the default implementation, it should probably be an explicit
asm("cpuid") to make it clear that we don't want any paravirtualized cpuid.

J