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    SubjectRe: [PATCH RFC] x86: check for and defend against BIOS memory corruption

    * Rafał Miłecki <> wrote:

    > 2008/8/28 Jeremy Fitzhardinge <>:
    > > Some BIOSes have been observed to corrupt memory in the low 64k. This
    > > patch does two things:
    > > - Reserves all memory which does not have to be in that area, to
    > > prevent it from being used as general memory by the kernel. Things
    > > like the SMP trampoline are still in the memory, however.
    > > - Clears the reserved memory so we can observe changes to it.
    > > - Adds a function check_for_bios_corruption() which checks and reports on
    > > memory becoming unexpectedly non-zero. Currently it's called in the
    > > x86 fault handler, and the powermanagement debug output.
    > >
    > > RFC: What other places should we check for corruption in?
    > >
    > > [ Alan, Rafał: could you check you see:
    > > 1: corruption messages
    > > 2: no crashes
    > > Thanks -J
    > > ]
    > I was trying my best to crash system with this patch applied and failed :)
    > Works great.
    > Just wonder if I should expect any printk from
    > check_for_bios_corruption? I do not see any:
    > zajec@sony:~> dmesg | grep -i corr
    > scanning 2 areas for BIOS corruption

    that's _very_ weird.

    maybe the BIOS expects _zeroes_ somewhere? Do you suddenly see crashes
    if you change this line in Jeremy's patch:

    + memset(__va(addr), 0, size);

    to something like:

    + memset(__va(addr), 0x55, size);

    If this does not tickle any messages either, then maybe the problem is
    in the identity of the entities we allocate in the first 64K. Is there a
    list of allocations that go there when Jeremy's patch is not applied?

    but ... i think with an earlier patch you saw corruption, right?
    Far-fetched idea: maybe it's some CPU erratum during suspend/resume that
    corrupts pagetables if the pagetables are allocated in the first 64K of
    RAM? In that case we should use a bootmem allocation for pagetables that
    give a minimum address of 64K.

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      Last update: 2008-08-29 08:49    [W:0.030 / U:80.616 seconds]
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