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    SubjectRe: [Patch 1/4][kernel][slimdump] Add new elf-note of type NT_NOCOREDUMP to capture slimdump
    On Wed, Oct 05, 2011 at 12:48:44PM +0530, K.Prasad wrote:
    > On Tue, Oct 04, 2011 at 10:04:37AM -0400, Vivek Goyal wrote:
    > > On Mon, Oct 03, 2011 at 01:02:03PM +0530, K.Prasad wrote:
    > > > There are certain types of crashes induced by faulty hardware in which
    > > > capturing crashing kernel's memory (through kdump) makes no sense (or sometimes
    > > > dangerous).
    > > >
    > > > A case in point, is unrecoverable memory errors (resulting in fatal machine
    > > > check exceptions) in which reading from the faulty memory location from the
    > > > kexec'ed kernel will cause double fault and system reset (leaving no
    > > > information for the user).
    > >
    > > Prasad,
    > >
    > > I am just trying to remember what was wrong with Andi's approach of
    > > disable MCE while copying the dump?
    > >
    >
    > Hi Vivek,
    > The behaviour upon a read operation on an UC memory location is
    > undefined and so we want to avoid it (previously discussed here:
    > http://article.gmane.org/gmane.linux.kernel/1146799). When we disable
    > MCE and copy the dump, we will invariably read the faulty memory
    > location.

    Right, from the message above:

    "- To disable MCE exceptions as done by the patches cited above. However
    the result of a read operation on corrupted memory is unknown and the
    system behaviour is undefined. We're unsure if this is a safe thing to
    do."

    Can you elaborate more on that? Are we talking poisoned memory here or
    undetected and uncorrectable memory errors?

    Thanks.

    --
    Regards/Gruss,
    Boris.


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