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    Subject[PATCH 4.9 022/241] x86/mce: Handle broadcasted MCE gracefully with kexec
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

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

    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;

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