Re: [PATCH 2/2] cpu: intel, amd: mask cleared cpuid features

["H. Peter Anvin" <hpa@zytor.com>]

On 07/20/2012 11:21 AM, Vladimir Davydov wrote:
>>
>> I am a bit concerned about this patch:
>>
>> 1. it silently changes existing behavior.
>
> Yes, but who needs the current implementation of 'clearcpuid' which,
> in fact, just hides flags in /proc/cpuinfo while userspace apps will
> see and consequently use all CPU features?

Anyone who wants to disable a feature from the kernel, specifically.

> So, I think it logically extends the existing behavior.
>
>> 2. even on enabled hardware, only some of the bits are maskable.
>
> The patch makes only words 0, 1, 4, 6 maskable, but words 3, 7, 8 are Linux-defined, words 2 and 5 are Transmeta-, Centaur-, etc- defined, and word 9 contains some bizarre Intel CPU features. Thus, it is words 0, 1, 4, 6 that contain useful information for most hardware models.

"Bizarre"?  New features, perhaps.

> If you ask about some Intel CPUs that can't mask CPUID function 0x80000001, this function describes AMD-specific features, and I bet those Intel CPUs just don't have them at all and thus have nothing to mask.

Not quite.

	-hpa



-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.