From 280a9ca5d0663b185ddc4443052076c29652a328 Mon Sep 17 00:00:00 2001 From: Dmitry Adamushko Date: Sat, 20 Dec 2008 00:15:24 +0100 Subject: x86: fix resume (S2R) broken by Intel microcode module, on A110L 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 Date : 2008-11-25 08:48 (19 days old) Handled-By : Dmitry Adamushko [ 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: Andreas Mohr Signed-off-by: Dmitry Adamushko Tested-by: Andreas Mohr Signed-off-by: Ingo Molnar Cc: Signed-off-by: Ingo Molnar --- arch/x86/kernel/microcode_intel.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'arch/x86/kernel/microcode_intel.c') diff --git a/arch/x86/kernel/microcode_intel.c b/arch/x86/kernel/microcode_intel.c index 622dc4a2178..a8e62792d17 100644 --- a/arch/x86/kernel/microcode_intel.c +++ b/arch/x86/kernel/microcode_intel.c @@ -155,6 +155,7 @@ static DEFINE_SPINLOCK(microcode_update_lock); static int collect_cpu_info(int cpu_num, struct cpu_signature *csig) { struct cpuinfo_x86 *c = &cpu_data(cpu_num); + unsigned long flags; unsigned int val[2]; memset(csig, 0, sizeof(*csig)); @@ -174,11 +175,16 @@ static int collect_cpu_info(int cpu_num, struct cpu_signature *csig) csig->pf = 1 << ((val[1] >> 18) & 7); } + /* serialize access to the physical write to MSR 0x79 */ + spin_lock_irqsave(µcode_update_lock, flags); + wrmsr(MSR_IA32_UCODE_REV, 0, 0); /* see notes above for revision 1.07. Apparent chip bug */ sync_core(); /* get the current revision from MSR 0x8B */ rdmsr(MSR_IA32_UCODE_REV, val[0], csig->rev); + spin_unlock_irqrestore(µcode_update_lock, flags); + pr_debug("microcode: collect_cpu_info : sig=0x%x, pf=0x%x, rev=0x%x\n", csig->sig, csig->pf, csig->rev); -- cgit v1.2.3-70-g09d2