x86/cpu: Add workaround for MONITOR instruction erratum on Goldmont based CPUs

Monitored cached line may not wake up from mwait on certain
Goldmont based CPUs. This patch will avoid calling
current_set_polling_and_test() and thereby not set the TIF_ flag.
The result is that we'll always send IPIs for wakeups.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1468867270-18493-1-git-send-email-jacob.jun.pan@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/cpufeatures.h

@@ -310,5 +310,5 @@
 #endif
 #define X86_BUG_NULL_SEG	X86_BUG(10) /* Nulling a selector preserves the base */
 #define X86_BUG_SWAPGS_FENCE	X86_BUG(11) /* SWAPGS without input dep on GS */
-
+#define X86_BUG_MONITOR		X86_BUG(12) /* IPI required to wake up remote CPU */
 #endif /* _ASM_X86_CPUFEATURES_H */

arch/x86/include/asm/mwait.h

@@ -97,7 +97,7 @@ static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
  */
 static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
 {
-	if (!current_set_polling_and_test()) {
+	if (static_cpu_has_bug(X86_BUG_MONITOR) || !current_set_polling_and_test()) {
 		if (static_cpu_has_bug(X86_BUG_CLFLUSH_MONITOR)) {
 			mb();
 			clflush((void *)&current_thread_info()->flags);

arch/x86/kernel/cpu/intel.c

@@ -13,6 +13,7 @@
 #include <asm/msr.h>
 #include <asm/bugs.h>
 #include <asm/cpu.h>
+#include <asm/intel-family.h>
 
 #ifdef CONFIG_X86_64
 #include <linux/topology.h>
@@ -508,6 +509,10 @@ static void init_intel(struct cpuinfo_x86 *c)
 	    (c->x86_model == 29 || c->x86_model == 46 || c->x86_model == 47))
 		set_cpu_bug(c, X86_BUG_CLFLUSH_MONITOR);
 
+	if (c->x86 == 6 && boot_cpu_has(X86_FEATURE_MWAIT) &&
+		((c->x86_model == INTEL_FAM6_ATOM_GOLDMONT)))
+		set_cpu_bug(c, X86_BUG_MONITOR);
+
 #ifdef CONFIG_X86_64
 	if (c->x86 == 15)
 		c->x86_cache_alignment = c->x86_clflush_size * 2;

arch/x86/kernel/process.c

@@ -404,7 +404,7 @@ static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
 	if (c->x86_vendor != X86_VENDOR_INTEL)
 		return 0;
 
-	if (!cpu_has(c, X86_FEATURE_MWAIT))
+	if (!cpu_has(c, X86_FEATURE_MWAIT) || static_cpu_has_bug(X86_BUG_MONITOR))
 		return 0;
 
 	return 1;