linux-kernel - [Patch V2] x86, mce: Ensure offline CPU's don't participate in mce rendezvous process.

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Message-ID: <20151205002930.GA24005@otc-brkl-03.jf.intel.com>
Date:	Fri, 4 Dec 2015 19:29:36 -0500
From:	Ashok Raj <ashok.raj@...el.com>
To:	linux-kernel@...r.kernel.org
Cc:	Boris Petkov <bp@...e.de>, linux-edac@...r.kernel.org,
	Tony Luck <tony.luck@...el.com>,
	Ashok Raj <ashok.raj@...el.com>
Subject: [Patch V2] x86, mce: Ensure offline CPU's don't participate in mce
 rendezvous process.

Linux has logical cpu offline capability. That can be triggered by:

# echo 0 > /sys/devices/system/cpu/cpuX/online

In Intel Architecture, MCE's are broadcasted to all CPUs in the system.

This includes the CPUs marked offline by Linux. Unless the CPU's were removed
via an ACPI notification, in which case the cpu's are removed from the
cpu_present_map.

This patch ensures offline CPU's don't participate in MCE rendezvous, but
simply perform clearing some status bits to ensure a second MCE wont cause
automatic shutdown.

Without the patch, mce_start will increment mce_callin, but mce_start would
only wait for all online_cpus. So offline cpu's should avoid participating
in the rendezvous process.

Reviewed-by: Tony Luck <tony.luck@...el.com>
Cc: stable@...r.kernel.org
Signed-off-by: Ashok Raj <ashok.raj@...el.com>
---
 arch/x86/kernel/cpu/mcheck/mce.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index c5b0d56..23ecb1d 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -998,7 +998,20 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 	u64 recover_paddr = ~0ull;
 	int flags = MF_ACTION_REQUIRED;
 	int lmce = 0;
+	unsigned int cpu = smp_processor_id();
+
+	/*
+	 * if this cpu is offline, just bail out.
+	 */
+	if (cpu_is_offline(cpu)) {
+		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);
-- 
2.4.3

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