[Xen-changelog] [xen master] x86/crash: disable the watchdog NMIs on the crashing cpu

[patchbot@xxxxxxx]

commit 2a16fcd5ba0244fef764886211452acc69c0ed00
Author:     David Vrabel <david.vrabel@xxxxxxxxxx>
AuthorDate: Fri Nov 22 14:48:12 2013 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Nov 22 14:48:12 2013 +0100

    x86/crash: disable the watchdog NMIs on the crashing cpu
    
    nmi_shootdown_cpus() is called during a crash to park all the other
    CPUs.  This changes the NMI trap handlers which means there's no point
    in having the watchdog still running.
    
    This also disables the watchdog before executing any crash kexec image
    and prevents the image from receiving unexpected NMIs.
    
    Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
    
    PVOps Linux as a kexec image shoots itself in the foot otherwise.
    
    On a Core2 system, Linux declares a firmware bug and tries to invert some 
bits
    in the performance counter register.  It ends up setting the number of 
retired
    instructions to generate another NMI to fewer instructions than the NMI
    interrupt path itself, and ceases to make any useful progress.
    
    The call to disable_lapic_nmi_watchdog() must be this late into the kexec 
path
    to be sure that this cpu is the one which will execute the kexec image.
    Otherwise there are race conditions where the NMIs might be disabled on the
    wrong cpu, resulting in the kexec image still receiving NMIs.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/crash.c       |    1 +
 xen/arch/x86/nmi.c         |    2 +-
 xen/include/asm-x86/apic.h |    1 +
 3 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/xen/arch/x86/crash.c b/xen/arch/x86/crash.c
index 4ef379b..01fd906 100644
--- a/xen/arch/x86/crash.c
+++ b/xen/arch/x86/crash.c
@@ -118,6 +118,7 @@ static void nmi_shootdown_cpus(void)
     unsigned long msecs;
     int i, cpu = smp_processor_id();
 
+    disable_lapic_nmi_watchdog();
     local_irq_disable();
 
     crashing_cpu = cpu;
diff --git a/xen/arch/x86/nmi.c b/xen/arch/x86/nmi.c
index 2c16d93..c67a9c3 100644
--- a/xen/arch/x86/nmi.c
+++ b/xen/arch/x86/nmi.c
@@ -165,7 +165,7 @@ static void nmi_timer_fn(void *unused)
     set_timer(&this_cpu(nmi_timer), NOW() + MILLISECS(1000));
 }
 
-static void disable_lapic_nmi_watchdog(void)
+void disable_lapic_nmi_watchdog(void)
 {
     if (nmi_active <= 0)
         return;
diff --git a/xen/include/asm-x86/apic.h b/xen/include/asm-x86/apic.h
index dd528fb..43b39ce 100644
--- a/xen/include/asm-x86/apic.h
+++ b/xen/include/asm-x86/apic.h
@@ -200,6 +200,7 @@ extern void smp_local_timer_interrupt (struct cpu_user_regs 
*regs);
 extern void setup_boot_APIC_clock (void);
 extern void setup_secondary_APIC_clock (void);
 extern void setup_apic_nmi_watchdog (void);
+extern void disable_lapic_nmi_watchdog(void);
 extern int reserve_lapic_nmi(void);
 extern void release_lapic_nmi(void);
 extern void self_nmi(void);
--
generated by git-patchbot for /home/xen/git/xen.git#master

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