[Patch V0] x86, mce: Ensure offline CPU's don't participate in mce rendezvous process.

[Ashok Raj]

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
wait for all online_cpus. So offline cpu's should avoid participating in the
rendezvous process.

Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
---
 arch/x86/kernel/cpu/mcheck/mce.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index c5b0d56..82a0c8b 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -998,6 +998,7 @@ 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();
 
 	ist_enter(regs);
 
@@ -1008,6 +1009,14 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 
 	mce_gather_info(&m, regs);
 
+	/*
+	 * if this cpu is offline, just bail out.
+	 * TBD: looking into adding any logs this offline CPU might have,
+	 * to be collected and reported by the rendezvous master.
+	 */
+	if (cpu_is_offline(cpu) && (m.mcgstatus & MCG_STATUS_RIPV))
+		goto out;
+
 	final = this_cpu_ptr(&mces_seen);
 	*final = m;
 
@@ -1142,8 +1151,8 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 
 	if (worst > 0)
 		mce_report_event(regs);
-	mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
 out:
+	mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
 	sync_core();
 
 	if (recover_paddr == ~0ull)
-- 
2.4.3

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