Re: [PATCH 1/4] x86: introduce hypervisor_cpuid_base()

Paolo Bonzini
2013-07-23T11:16:04Z

Il 23/07/2013 12:04, H. Peter Anvin ha scritto:
> On 07/23/2013 02:41 AM, Jason Wang wrote:
>>
>> +static inline uint32_t hypervisor_cpuid_base(const char *sig, uint32_t leaves)
>> +{
>> + uint32_t base, eax, ebx, ecx, edx;
>> + char signature[13];
>> +
>> + for (base = 0x40000000; base < 0x40010000; base += 0x100) {
>> + cpuid(base, &eax, &ebx, &ecx, &edx);
>> + *(uint32_t *)(signature + 0) = ebx;
>> + *(uint32_t *)(signature + 4) = ecx;
>> + *(uint32_t *)(signature + 8) = edx;
>> + signature[12] = 0;
>> +
>> + if (!strcmp(sig, signature) &&
>> + (leaves == 0 || ((eax - base) >= leaves)))
>> + return base;
>> + }
>> +
>> + return 0;
>> +}
>> +
>
> Hmm... how about:
>
> uint32_t sign[3];
>
> cpuid(base, &eax, &sign[0], &sign[1], &sign[2]);
>
> if (!memcmp(sig, sign, 12) && ...);

That's nicer, though strcmp is what the replaced code used to do in
patches 2 and 3.

Note that memcmp requires the caller to use "KVMKVMKVM\0\0" as the
signature (or alternatively hypervisor_cpuid_base can copy the argument
into another 12-byte local variable).

Paolo