linux-kernel - [PATCH 3.16.y-ckt 118/128] x86/mce: Ensure offline CPUs don't participate in rendezvous process

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Message-Id: <1453672883-2708-119-git-send-email-luis.henriques@canonical.com>
Date:	Sun, 24 Jan 2016 22:01:13 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Ashok Raj <ashok.raj@...el.com>, Borislav Petkov <bp@...e.de>,
	"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>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 118/128] x86/mce: Ensure offline CPUs don't participate in rendezvous process

3.16.7-ckt23 -stable review patch.  If anyone has any objections, please let me know.

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

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>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@...onical.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 5648b506f3ae..8ae7e3f27b1b 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -1042,6 +1042,17 @@ 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)