• Dmitry Adamushko's avatar
    x86: fix resume (S2R) broken by Intel microcode module, on A110L · 280a9ca5
    Dmitry Adamushko authored
    Impact: fix deadlock
    
    This is in response to the following bug report:
    
    Bug-Entry       : http://bugzilla.kernel.org/show_bug.cgi?id=12100
    Subject         : resume (S2R) broken by Intel microcode module, on A110L
    Submitter       : Andreas Mohr <andi@lisas.de>
    Date            : 2008-11-25 08:48 (19 days old)
    Handled-By      : Dmitry Adamushko <dmitry.adamushko@gmail.com>
    
    [ The deadlock scenario has been discovered by Andreas Mohr ]
    
    I think I might have a logical explanation why the system:
    
      (http://bugzilla.kernel.org/show_bug.cgi?id=12100)
    
    might hang upon resuming, OTOH it should have likely hanged each and every time.
    
    (1) possible deadlock in microcode_resume_cpu() if either 'if' section is
    taken;
    
    (2) now, I don't see it in spec. and can't experimentally verify it (newer
    ucodes don't seem to be available for my Core2duo)... but logically-wise, I'd
    think that when read upon resuming, the 'microcode revision' (MSR 0x8B) should
    be back to its original one (we need to reload ucode anyway so it doesn't seem
    logical if a cpu doesn't drop the version)... if so, the comparison with
    memcmp() for the full 'struct cpu_signature' is wrong... and that's how one of
    the aforementioned 'if' sections might have been triggered - leading to a
    deadlock.
    
    Obviously, in my tests I simulated loading/resuming with the ucode of the same
    version (just to see that the file is loaded/re-loaded upon resuming) so this
    issue has never popped up.
    
    I'd appreciate if someone with an appropriate system might give a try to the
    2nd patch (titled "fix a comparison && deadlock...").
    
    In any case, the deadlock situation is a must-have fix.
    Reported-by: default avatarAndreas Mohr <andi@lisas.de>
    Signed-off-by: default avatarDmitry Adamushko <dmitry.adamushko@gmail.com>
    Tested-by: default avatarAndreas Mohr <andi@lisas.de>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    Cc: <stable@kernel.org>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    280a9ca5
microcode_core.c 13.2 KB