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    SubjectRe: [RFC][PATCH 3/3] x86: make MP a required-feature on 64-bit
    On 06/20/2014 10:43 AM, Borislav Petkov wrote:
    > On Fri, Jun 20, 2014 at 09:37:57AM -0700, H. Peter Anvin wrote:
    >> We probably should just the cpu_has_mp macro entirely. All it is used
    >> for is printing a warning in amd_k7_smp_check().
    >>
    >> Andi, Borislav -- as far as I can tell, we have *never* enforced this on
    >> the 64-bit kernel, although we have enforced it on 64-bit processors
    >> running the 32-bit kernel. We should either enforce it on both or just
    >> drop it. What is your opinion?
    >
    > Well, my AMD CPUID guide says CPUID Fn8000_0001_EDX[19] is reserved,
    > i.e. that X86_FEATURE_MP bit will be probably cleared.
    >
    > And so it is, on my F15h AMD it is not set:
    >
    > eax in: 0x80000001, eax = 00600f20 ebx = 10000000 ecx = 01ebbfff edx = 2fd3fbff
    > ^
    > ----------|
    >
    > So I don't think we should enforce it on 64-bit.
    >
    > I guess we can leave the check in amd_k7_smp_check() though but remove that
    > nasty cpu_has_mp macro and do static_cpu_has() instead.
    >
    > My 2¢ only.
    >

    This is run before static_cpu_has().

    The point, though, was that we "enforce" (taint) on 32 bits but not on
    64 bits, which is clearly wrong.

    My inclination is to completely kill amd_k7_smp_check() entirely, since
    noone seems to know when it actually matters and it is clearly historic.

    -hpa

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