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Subject[PATCH 3.19.y-ckt 123/160] x86/mce: Ensure offline CPUs don't participate in rendezvous process
Date
3.19.8-ckt13 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Ashok Raj <ashok.raj@intel.com>

commit d90167a941f62860f35eb960e1012aa2d30e7e94 upstream.

Intel's MCA implementation broadcasts MCEs to all CPUs on the
node. This poses a problem for offlined CPUs which cannot
participate in the rendezvous process:

Kernel panic - not syncing: Timeout: Not all CPUs entered broadcast exception handler
Kernel Offset: disabled
Rebooting in 100 seconds..

More specifically, Linux does a soft offline of a CPU when
writing a 0 to /sys/devices/system/cpu/cpuX/online, which
doesn't prevent the #MC exception from being broadcasted to that
CPU.

Ensure that offline CPUs don't participate in the MCE rendezvous
and clear the RIP valid status bit so that a second MCE won't
cause a shutdown.

Without the patch, mce_start() will increment mce_callin and
wait for all CPUs. Offlined CPUs should avoid participating in
the rendezvous process altogether.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
[ Massage commit message. ]
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/1449742346-21470-2-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
arch/x86/kernel/cpu/mcheck/mce.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 1596e04..c3f58e9 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -1088,6 +1088,17 @@ void do_machine_check(struct pt_regs *regs, long error_code)
DECLARE_BITMAP(valid_banks, MAX_NR_BANKS);
char *msg = "Unknown";

+ /* If this CPU is offline, just bail out. */
+ if (cpu_is_offline(smp_processor_id())) {
+ u64 mcgstatus;
+
+ mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);
+ if (mcgstatus & MCG_STATUS_RIPV) {
+ mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
+ return;
+ }
+ }
+
this_cpu_inc(mce_exception_count);

if (!cfg->banks)
--
1.9.1

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