Messages in this thread | | | Date | Fri, 20 Jul 2012 13:19:20 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH 2/2] cpu: intel, amd: mask cleared cpuid features |
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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.
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