linux-kernel - [PATCH 4.3 005/157] x86/mce: Ensure offline CPUs dont participate in rendezvous process

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Date:	Wed, 27 Jan 2016 10:11:12 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Ashok Raj <ashok.raj@...el.com>,
	Borislav Petkov <bp@...e.de>, Tony Luck <tony.luck@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-edac <linux-edac@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 4.3 005/157] x86/mce: Ensure offline CPUs dont participate in rendezvous process

4.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ashok Raj <ashok.raj@...el.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@...el.com>
[ Massage commit message. ]
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-edac <linux-edac@...r.kernel.org>
Link: http://lkml.kernel.org/r/1449742346-21470-2-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kernel/cpu/mcheck/mce.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -999,6 +999,17 @@ void do_machine_check(struct pt_regs *re
 	int flags = MF_ACTION_REQUIRED;
 	int lmce = 0;

+	/* 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;
+		}
+	}
+
 	ist_enter(regs);

 	this_cpu_inc(mce_exception_count);