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Subject[PATCH 02/15] x86/split_lock: Set up #AC exception for split locked accesses
Date
When bit 29 is set in Test Control MSR register 0x33, #AC exception
is generated for split locked accesses at all CPL.

By default, kernel inherits the bit setting from BIOS.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
---
arch/x86/include/asm/cpu.h | 2 ++
arch/x86/kernel/cpu/common.c | 2 ++
arch/x86/kernel/cpu/split_lock.c | 54 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 58 insertions(+)

diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index c73b6d369047..b4fe6496bb15 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -42,7 +42,9 @@ unsigned int x86_model(unsigned int sig);
unsigned int x86_stepping(unsigned int sig);
#ifdef CONFIG_SPLIT_LOCK_AC
int __init enumerate_split_lock(void);
+void setup_split_lock(void);
#else /* CONFIG_SPLIT_LOCK_AC */
static inline int enumerate_split_lock(void) { return 0; }
+static inline void setup_split_lock(void) {}
#endif /* CONFIG_SPLIT_LOCK_AC */
#endif /* _ASM_X86_CPU_H */
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 7684e82e254f..daff18ef4f8f 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1304,6 +1304,8 @@ static void identify_cpu(struct cpuinfo_x86 *c)
/* Init Machine Check Exception if available. */
mcheck_cpu_init(c);

+ setup_split_lock();
+
select_idle_routine(c);

#ifdef CONFIG_NUMA
diff --git a/arch/x86/kernel/cpu/split_lock.c b/arch/x86/kernel/cpu/split_lock.c
index 2ab28419e080..98bbfb176cf4 100644
--- a/arch/x86/kernel/cpu/split_lock.c
+++ b/arch/x86/kernel/cpu/split_lock.c
@@ -15,6 +15,11 @@

static bool split_lock_ac_supported;

+#define DISABLE_SPLIT_LOCK_AC 0
+#define ENABLE_SPLIT_LOCK_AC 1
+
+static int split_lock_ac = DISABLE_SPLIT_LOCK_AC;
+
/*
* On processors not supporting #AC exception for split lock feature,
* MSR_TEST_CTL may not exist or MSR_TEST_CTL exists but the bit 29 is
@@ -58,5 +63,54 @@ void __init enumerate_split_lock(void)
*/
wrmsr(MSR_TEST_CTL, l_orig, h);

+ /* Initialize split lock setting from previous BIOS setting. */
+ if (l_orig & MSR_TEST_CTL_ENABLE_AC_SPLIT_LOCK)
+ split_lock_ac = ENABLE_SPLIT_LOCK_AC;
+ else
+ split_lock_ac = DISABLE_SPLIT_LOCK_AC;
+
pr_info("#AC exception for split locked accesses is supported\n");
}
+
+static bool _setup_split_lock(int split_lock_ac_val)
+{
+ u32 l, h;
+
+ rdmsr(MSR_TEST_CTL, l, h);
+
+ /* No need to update MSR if same value. */
+ if ((l >> MSR_TEST_CTL_ENABLE_AC_SPLIT_LOCK_SHIFT & 0x1) ==
+ split_lock_ac_val)
+ goto out;
+
+ if (split_lock_ac_val == ENABLE_SPLIT_LOCK_AC)
+ /* Set the split lock bit to enable the feature. */
+ l |= MSR_TEST_CTL_ENABLE_AC_SPLIT_LOCK;
+ else if (split_lock_ac_val == DISABLE_SPLIT_LOCK_AC)
+ /* Clear the split lock bit to disable the feature. */
+ l &= ~MSR_TEST_CTL_ENABLE_AC_SPLIT_LOCK;
+ else
+ return false;
+
+ wrmsr(MSR_TEST_CTL, l, h);
+out:
+ return true;
+}
+
+void setup_split_lock(void)
+{
+ if (!split_lock_ac_supported)
+ return;
+
+ if (!_setup_split_lock(split_lock_ac))
+ goto out_fail;
+
+ pr_info_once("split lock #AC is %sd\n",
+ split_lock_ac == ENABLE_SPLIT_LOCK_AC ? "enable"
+ : "disable");
+
+ return;
+
+out_fail:
+ pr_warn("fail to set split lock #AC\n");
+}
--
2.5.0
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