x86/smpboot: Don't use mwait_play_dead() on AMD systems

Recent AMD systems support using MWAIT for C1 state. However, MWAIT will
not allow deeper cstates than C1 on current systems.

play_dead() expects to use the deepest state available.  The deepest state
available on AMD systems is reached through SystemIO or HALT. If MWAIT is
available, it is preferred over the other methods, so the CPU never reaches
the deepest possible state.

Don't try to use MWAIT to play_dead() on AMD systems. Instead, use CPUIDLE
to enter the deepest state advertised by firmware. If CPUIDLE is not
available then fallback to HALT.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org
Cc: Yazen Ghannam <Yazen.Ghannam@amd.com>
Link: https://lkml.kernel.org/r/20180403140228.58540-1-Yazen.Ghannam@amd.com

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 45175b81dd5b371e188820fddefcfd5ee6c8bee9..0f1cbb042f49b82e7a01b7ace0bce08061a8e6f1 100644 (file)
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1571,6 +1571,8 @@ static inline void mwait_play_dead(void)
        void *mwait_ptr;
        int i;
 
+       if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
+               return;
        if (!this_cpu_has(X86_FEATURE_MWAIT))
                return;
        if (!this_cpu_has(X86_FEATURE_CLFLUSH))