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    SubjectRe: [PATCH 1/2] kmemcheck v3
    On Fri, Feb 08, 2008 at 01:18:37PM +0100, Vegard Nossum wrote:
    > On 2/8/08, Andi Kleen <andi@firstfloor.org> wrote:
    > > Your assumption that only the string instructions can take
    > > multiple page faults seems a little dangerous too.
    >
    > Yes, this is true. I cannot guarantee that there are no other
    > instructions that could access more than one memory location but only
    > take one page fault. However, since the kernel does boot, we at least
    > know that these instructions are not very frequently used. (If you
    > know of any other instructions we might be missing, I'll be happy to
    > know about it!)

    Pretty much all in the right circumstances.

    e.g. consider a segment reload in tracked memory.

    Also there are various instructions which do all kinds of complicated
    things internally; like IRET or INT: often with many memory accesses.
    Just page through a instruction manual and look at the pseudo code
    describing what the various instructions do.

    >
    > There is also the point that if kmemcheck doesn't handle all the
    > faulting addresses, it will simply fault again and again, without
    > making any progress. I mean, it won't go unnoticed for very long :-)
    >
    > This is also why we depend on M386 and !X86_GENERIC, to avoid those
    > MMX, etc. instructions, as we have no support for those currently

    I would not expect problems from MMX/SSE here (except for the generic
    ones all instructions have)

    -Andi



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