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    SubjectRe: [patch] SMP alternatives
    On Wed, Nov 23, 2005 at 09:44:05PM +0000, Alan Cox wrote:
    > On Mer, 2005-11-23 at 10:42 -0800, Linus Torvalds wrote:
    > > Of course, if it's in one of the low 12 bits of %cr3, there would have to
    > > be a "enable this bit" in %cr4 or something. Historically, you could write
    > > any crap in the low bits, I think.
    >
    > There is a much much better way to do it than just user space and
    > without hitting cr3/cr4 - put "lock works" in the PAT and while we'll
    > have to add PAT support which we need to do anyway we would get a world
    > where on uniprocessor lock prefix only works on addresse targets we want
    > it to - ie pci_alloc_consistent() pages.

    The idea was to turn LOCK on only if the process has any
    shared writable mapping and num_online_cpus() > 0.

    Might be a bit costly to rewrite all the page tables for that case
    just to change the PAT index. A bit is nicer for that.

    -Andi
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