This is a note to let you know that I've just added the patch titled

x86/mce: Handle broadcasted MCE gracefully with kexec

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-mce-handle-broadcasted-mce-gracefully-with-kexec.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Sun Mar 18 16:55:33 CET 2018

From: Xunlei Pang xlpang@redhat.com Date: Mon, 13 Mar 2017 10:50:19 +0100 Subject: x86/mce: Handle broadcasted MCE gracefully with kexec

From: Xunlei Pang xlpang@redhat.com

[ Upstream commit 5bc329503e8191c91c4c40836f062ef771d8ba83 ]

When we are about to kexec a crash kernel and right then and there a broadcasted MCE fires while we're still in the first kernel and while the other CPUs remain in a holding pattern, the #MC handler of the first kernel will timeout and then panic due to never completing MCE synchronization.

Handle this in a similar way as to when the CPUs are offlined when that broadcasted MCE happens.

[ Boris: rewrote commit message and comments. ]

Suggested-by: Borislav Petkov bp@alien8.de Signed-off-by: Xunlei Pang xlpang@redhat.com Signed-off-by: Borislav Petkov bp@suse.de Acked-by: Tony Luck tony.luck@intel.com Cc: Naoya Horiguchi n-horiguchi@ah.jp.nec.com Cc: kexec@lists.infradead.org Cc: linux-edac linux-edac@vger.kernel.org Link: http://lkml.kernel.org/r/1487857012-9059-1-git-send-email-xlpang@redhat.com Link: http://lkml.kernel.org/r/20170313095019.19351-1-bp@alien8.de Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/reboot.h | 1 + arch/x86/kernel/cpu/mcheck/mce.c | 18 ++++++++++++++++-- arch/x86/kernel/reboot.c | 5 +++-- 3 files changed, 20 insertions(+), 4 deletions(-)

--- a/arch/x86/include/asm/reboot.h +++ b/arch/x86/include/asm/reboot.h @@ -15,6 +15,7 @@ struct machine_ops { };

extern struct machine_ops machine_ops; +extern int crashing_cpu;

void native_machine_crash_shutdown(struct pt_regs *regs); void native_machine_shutdown(void); --- a/arch/x86/kernel/cpu/mcheck/mce.c +++ b/arch/x86/kernel/cpu/mcheck/mce.c @@ -48,6 +48,7 @@ #include <asm/tlbflush.h> #include <asm/mce.h> #include <asm/msr.h> +#include <asm/reboot.h>

#include "mce-internal.h"

@@ -1081,9 +1082,22 @@ void do_machine_check(struct pt_regs *re * on Intel. */ int lmce = 1; + int cpu = smp_processor_id();

- /* If this CPU is offline, just bail out. */ - if (cpu_is_offline(smp_processor_id())) { + /* + * Cases where we avoid rendezvous handler timeout: + * 1) If this CPU is offline. + * + * 2) If crashing_cpu was set, e.g. we're entering kdump and we need to + * skip those CPUs which remain looping in the 1st kernel - see + * crash_nmi_callback(). + * + * Note: there still is a small window between kexec-ing and the new, + * kdump kernel establishing a new #MC handler where a broadcasted MCE + * might not get handled properly. + */ + if (cpu_is_offline(cpu) || + (crashing_cpu != -1 && crashing_cpu != cpu)) { u64 mcgstatus;

mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS); --- a/arch/x86/kernel/reboot.c +++ b/arch/x86/kernel/reboot.c @@ -769,10 +769,11 @@ void machine_crash_shutdown(struct pt_re #endif

+/* This is the CPU performing the emergency shutdown work. */ +int crashing_cpu = -1; + #if defined(CONFIG_SMP)

-/* This keeps a track of which one is crashing cpu. */ -static int crashing_cpu; static nmi_shootdown_cb shootdown_callback;

static atomic_t waiting_for_crash_ipi;

Patches currently in stable-queue which might be from xlpang@redhat.com are

queue-4.9/rtmutex-fix-pi-chain-order-integrity.patch queue-4.9/x86-mce-handle-broadcasted-mce-gracefully-with-kexec.patch