[PATCH] x86: add workaround monitor bug

[Jacob Pan]

From: Peter Zijlstra <pet...@infradead.org>

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 <pet...@infradead.org>
Signed-off-by: Jacob Pan <jacob.jun....@linux.intel.com>
---
 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/include/asm/mwait.h       | 2 +-
 arch/x86/kernel/cpu/intel.c        | 5 +++++
 arch/x86/kernel/process.c          | 2 +-
 4 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h 
b/arch/x86/include/asm/cpufeatures.h
index 78dbd28..197a3f4 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -304,6 +304,7 @@
 #define X86_BUG_SYSRET_SS_ATTRS        X86_BUG(8) /* SYSRET doesn't fix up SS 
attrs */
 #define X86_BUG_NULL_SEG       X86_BUG(9) /* Nulling a selector preserves the 
base */
 #define X86_BUG_SWAPGS_FENCE   X86_BUG(10) /* SWAPGS without input dep on GS */
+#define X86_BUG_MONITOR                X86_BUG(11) /* IPI required to wake up 
remote cpu */
 
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index 0deeb2d..f37f2d8 100644
--- a/arch/x86/include/asm/mwait.h
+++ b/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);
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 6e2ffbe..77c6b3e 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/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>
@@ -509,6 +510,10 @@ 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;
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 96becbb..59f68f1 100644
--- a/arch/x86/kernel/process.c
+++ b/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;
-- 
1.9.1