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    SubjectRe: [PATCH] [4/7] Don't use large pages to map the first 2/4MB of memory
    On Fri, Mar 21, 2008 at 07:03:19PM +0100, Thomas Gleixner wrote:
    > On Fri, 21 Mar 2008, Andi Kleen wrote:
    > > > Also we split the first GB mapping anyway due to the various regions
    > > > (NX, RO, UC) in there.
    > >
    > > I didn't think so unless you have DEBUG_RODATA enabled?
    >
    > NX is independent of DEBUG_RODATA

    Sure, but it is still not split by default. At least I don't see any code
    for that anywhere except in my own patchkit.

    > and the RODATA protection should be
    > made unconditional on anyway.

    Requiring hundreds instead of two TLB entries for the kernel text?

    I must say I personally cannot ever remember any bug caught by RODATA
    anyways, so I am a bit dubious on its value.

    > > Also there
    > > should be no UC region there as known by the kernel. There might
    > > be a WC region there from the frame buffer code, but that is an MTRR,
    > > not a pageattr.
    >
    > The first ioremap of the PCI space splits the GB page as well.

    PCI space is normally in the fourth or sometimes third GB page,
    not in the first. I am not aware of any system that has the PCI hole
    in the first GB.

    -Andi



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