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    SubjectRe: [patch 00/13] x86: PAT support updated - v3

    * <> wrote:

    > Follow up on earlier PAT patch series here:
    > This patch series adds Page Attribute Table (PAT) support on x86.
    > There have been few changes based on comments for earlier patches and
    > also issues that was seen while the earlier patchset was in mm. The
    > main changes include:
    > * Unlike earlier patchset, there are no changes to identity mapping of
    > reserved regions.
    > * Unlike earlier patches, there are no chanegs to early ioremap.
    > * We look at MTRR setting and PAT request and track the resultant type
    > to avoid aliasing.
    > * UC_MINUS in PAT to provide backward compatibility to /dem/mem mmap users.
    > In general, we have tried to make patches more simpler and cleaner.
    > Hope is to cause less disruption along the way. The changes/cleaups
    > that went into x86/mm (specifically pageattr.c) has helped us along
    > the way.
    > The patchset is against x86 testing from couple of days back.

    thanks Venki, i've queued this up so that we can see how well it goes.
    It now looks a lot less dangerous and more compatible than it did before
    - but i'm sure there'll be issues nevertheless :-/

    > There are two issues that we are leaving out at the moment to make the patch
    > simple. We will be addressing them with incremental patches soon:
    > * FB/DRM drivers using pgprot_val and changing protection on their own
    > without using any proper APIs like ioremap. There are few such usages and
    > each one will be addressed separately.
    > * To change attributes from WC to WB in a "perfect way", one has to follow
    > certain sequence like make page non-present etc.

    hm, until this is done correctly i guess we should disallow WC to WB
    transitions? A good number of erratas apply i suspect :-/


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