x86/mce: Always use 64-bit timestamps

The machine check timestamp uses get_seconds(), which returns an
'unsigned long' number that might overflow on 32-bit architectures (in
the distant future) and is therefore deprecated.

The normal replacement would be ktime_get_real_seconds(), but that needs
to use a sequence lock that might cause a deadlock if the MCE happens at
just the wrong moment. The __ktime_get_real_seconds() skips that lock
and is safer here, but has a miniscule risk of returning the wrong time
when we read it on a 32-bit architecture at the same time as updating
the epoch, i.e. from before y2106 overflow time to after, or vice versa.

This seems to be an acceptable risk in this particular case, and is the
same thing we do in kdb.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Cc: y2038@lists.linaro.org
Link: http://lkml.kernel.org/r/20180618100759.1921750-1-arnd@arndb.de

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index e93670d736a6af397d33fa35834e2c8b25e2b239..d62201e40027d9e177d267b53683277d042b0dd8 100644 (file)
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -123,8 +123,8 @@ void mce_setup(struct mce *m)
 {
        memset(m, 0, sizeof(struct mce));
        m->cpu = m->extcpu = smp_processor_id();
-       /* We hope get_seconds stays lockless */
-       m->time = get_seconds();
+       /* need the internal __ version to avoid deadlocks */
+       m->time = __ktime_get_real_seconds();
        m->cpuvendor = boot_cpu_data.x86_vendor;
        m->cpuid = cpuid_eax(1);
        m->socketid = cpu_data(m->extcpu).phys_proc_id;