On Tue, 2008-01-29 at 23:17 -0800, H. Peter Anvin wrote:
> Yi Yang wrote:
> >>
> >> It's broken, because it doesn't take into account the fact that Intel
> >> broke CPUID level 4 and made it "repeating" (neither did the cpuid char
> >> device, because it predated the Intel braindamage; I've had a patch for
> >> it privately for a while, but didn't push it upstream because paravirt
> >> broke it royally and I wanted the situation to settle down.)
>
> > level 4 doesn't result in repeating on Intel CPU, cpuid module sets
> > file offset to level, so cat /dev/cpu/*/cpuid will run cpuid instruction
> > continuously.
>
> The issue is that Intel suddenly made CPUID ECX-sensitive, which there
> is no way to represent.
Function cpuid has reset ecx to 0 immediate before calling to __cpuid,
so this shouldn't be a problem now.
in include/asm-x86/processor_32.h
/*
* Generic CPUID function
* clear %ecx since some cpus (Cyrix MII) do not set or clear %ecx
* resulting in stale register contents being returned.
*/
static inline void cpuid(unsigned int op,
unsigned int *eax, unsigned int *ebx,
unsigned int *ecx, unsigned int *edx)
{
*eax = op;
*ecx = 0;
__cpuid(eax, ebx, ecx, edx);
}
>
> As far as cat /dev/cpu/*/cpuid, that's a user error.
>
> -hpa
>
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