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    SubjectRe: [PATCH] x86, AMD: Correct F15h IC aliasing issue
    On 07/26/2011 12:42 PM, Andre Przywara wrote:
    >>
    >> In other words, it's completely ad hoc.
    >
    > There is no need to determine it by calculating, because it caused by
    > the special design of the BD L1 cache and thus fixed.
    > And a calculation would be even more confusing:
    >
    > The L1I is virtually indexed, but physically tagged.
    > 64KB L1I cache, 64 Bytes per Cacheline = 1024 cache lines
    > 1024 lines / 2 way associative = 512 indexes
    > 64 Bytes per Cacheline (6 bits) + 512 indexes (9 bits) = bits [14:0]
    > virtual and physical addresses are the same for bits [11:0], which
    > leaves the remaining 14:12 susceptible for aliasing.
    >
    > So bit 12 comes from PAGESIZE and yes, the 14 could be derived from the
    > CPUID cache info, but I don't see much value in breaking this down this way.
    > But I agree that there should be some comment in the patch which at
    > least notes that bits [14:12] are due to the L1I design, maybe we can
    > copy a nicer version of the above math in the commit message for reference.
    >

    The right thing to do this would be to have a bit in CPUID which would
    indicate that the kernel has to perform the above calculation -- because
    obviously not all CPUs have this issue. From that we can calculate a
    mask to insert into whatever appropriate location... depending on the
    exact tack we have to apply to deal with this situation.

    -hpa



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