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    SubjectRe: [git pull] core, x86: make LIST_POISON less deadly

    * Linus Torvalds <> wrote:

    > On Mon, 14 Jul 2008, Ingo Molnar wrote:
    > >
    > > + hex
    > > + default 0 if X86_32
    > > + default 0xffffc10000000000 if X86_64
    > This looks like a singularly bad pointer value on x86-64.
    > Why not pick something that is *guaranteed* to fault? The above looks
    > like any future setup that supports 41 bits of addressing and has
    > extended the page tables (yes, it will happen eventually) will find
    > that to be a perfectly valid address?
    > It's also visually confusing, since it's visually very close to a real
    > kernel pointer too.
    > Grr.
    > Why not use something sane like 0xdead000000000000, which has the high
    > bit set but very fundamentally isn't a valid pointer, and never will
    > be? And which is a *lot* more visually obvious too!

    initially i suggested that too - but such addresses raise a #GP instead
    of a page fault so their decoding is a bit harder.

    We dont do any instruction decoding in #GP handlers to figure out what
    happened, while in the pagefault case we know which address faulted,

    Perhaps we could try to make #GP handlers a bit more informative -
    although decoding instructions will make things a bit more fragile

    Perhaps make it 0xffffcdead0000000 ?

    in any case, please ignore this topic until it's all worked out - no
    other topics depend on this one so it can be skipped safely.


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