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    SubjectRe: [patch 02/11] PAT x86: Map only usable memory in x86_64 identity map and kernel text
    On Mon, Jan 14, 2008 at 05:43:24PM +0100, Ingo Molnar wrote:
    > * Pallipadi, Venkatesh <> wrote:
    > > Also, relying on MTRR, is like giving more importance to BIOS writer
    > > than required :-). I think the best way to deal with MTRR is just to
    > > not touch it. Leave it as it is and do not try to assume that they are
    > > correct, as frequently they will not be.
    > i'd suggest the following strategy on PAT-capable CPUs:
    > - do not try to write MTRRs. Ever.
    > - _read_ the current MTRR settings (including the default MTRR) and
    > check them against the e820 map. I can see two basic types of
    > mismatches:
    > - RAM area marked fine in e820 but marked UC by MTRR: this
    > currently results in a slow system.

    Time to resurrect Jesse's old patches
    i386-trim-memory-not-covered-by-wb-mtrrs.patch(which was in -mm sometime back)

    > (NOTE: UC- would be fine and
    > overridable by PAT, hence it's not a conflict we should detect.)

    UC- can't be specified by MTRR's.

    > - mmio area marked cacheable in the MTRR (results in broken system)

    PAT can help specify the UC/WC attribute here.


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