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    SubjectRe: [RFC] prevent "dd if=/dev/mem" crash
    On Sun, Oct 19, 2003 at 05:25:37AM -0600, Eric W. Biederman wrote:
    > We do have all of the information we need in struct page to see if a
    > page address is valid, so checking that is reasonable. I suspect it
    > will require some interesting variant of pfn_to_page to handle of the
    > weird sparse memory locations properly.

    It would be best to check the pfn before attempting to convert it to a
    struct page. The struct page * returned by arch code will be garbage in
    most instances, as none of the routines actually check validity
    internally. pfn_valid() is even bogus on most of them, so you'll have
    to walk pgdats by hand for this. The pfn_valid() checks work most of the
    time on PC's, but the first time someone runs X on a box with discontig
    and a bogus pfn_valid() they'll get fireworks (and in fact, it's already
    happened, but wasn't posted to lkml).

    -- wli
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