[PATCH] x86, smpboot: Call CLFLUSH only on X86_BUG_CLFLUSH_MONITOR-affected CPUs

[Borislav Petkov <bp@alien8.de>]

From: Borislav Petkov <bp@suse.de>
Subject: [PATCH] x86, smpboot: Call CLFLUSH only on X86_BUG_CLFLUSH_MONITOR-affected CPUs

Make the AAI65 erratum workaround for Xeon 7400 machines only instead of
punishing all CPUs doing idle with MWAIT with the CLFLUSH penalty.

Based on a patch originally by Scotty Bauer <sbauer@eng.utah.edu>.

Cc: Scotty Bauer <sbauer@eng.utah.edu>
Signed-off-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/kernel/smpboot.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 6d7022c683e3..771ebd6e8b77 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1432,7 +1432,11 @@ static inline void mwait_play_dead(void)
 		 * case where we return around the loop.
 		 */
 		mb();
-		clflush(mwait_ptr);
+
+		asm volatile(ALTERNATIVE("", "clflush %[p]",
+					 X86_BUG_CLFLUSH_MONITOR)
+				: [p] "+m" (*(unsigned long *)mwait_ptr));
+
 		mb();
 		__monitor(mwait_ptr, 0, 0);
 		mb();
-- 
2.2.0.33.gc18b867


-- 
Regards/Gruss,
    Boris.

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