linux-kernel - [PATCH V4 1/2] x86/msr: expose msr_flip

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Date:   Tue, 28 Mar 2017 18:45:19 -0700
From:   kan.liang@...el.com
To:     peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Cc:     bp@...en8.de, acme@...nel.org, eranian@...gle.com,
        jolsa@...nel.org, ak@...ux.intel.com,
        Kan Liang <Kan.liang@...el.com>
Subject: [PATCH V4 1/2] x86/msr: expose msr_flip_bit function

From: Kan Liang <Kan.liang@...el.com>

There is no exported kernel interfaces which can flip a MSR bit. It has
to do read-modify-write operation on the MSR through rd/wrmsr*
interfaces. But the method is not atomic.

There is already __flip_bit support. Just rename and expose it.

Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Kan Liang <Kan.liang@...el.com>
---
 arch/x86/include/asm/msr.h | 1 +
 arch/x86/lib/msr.c         | 7 ++++---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index 898dba2..c1e3026 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -312,6 +312,7 @@ struct msr *msrs_alloc(void);
 void msrs_free(struct msr *msrs);
 int msr_set_bit(u32 msr, u8 bit);
 int msr_clear_bit(u32 msr, u8 bit);
+int msr_flip_bit(u32 msr, u8 bit, bool set);
 
 #ifdef CONFIG_SMP
 int rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h);
diff --git a/arch/x86/lib/msr.c b/arch/x86/lib/msr.c
index 0776425..9bda539 100644
--- a/arch/x86/lib/msr.c
+++ b/arch/x86/lib/msr.c
@@ -58,7 +58,7 @@ int msr_write(u32 msr, struct msr *m)
 	return wrmsrl_safe(msr, m->q);
 }
 
-static inline int __flip_bit(u32 msr, u8 bit, bool set)
+int msr_flip_bit(u32 msr, u8 bit, bool set)
 {
 	struct msr m, m1;
 	int err = -EINVAL;
@@ -85,6 +85,7 @@ static inline int __flip_bit(u32 msr, u8 bit, bool set)
 
 	return 1;
 }
+EXPORT_SYMBOL_GPL(msr_flip_bit);
 
 /**
  * Set @bit in a MSR @msr.
@@ -96,7 +97,7 @@ static inline int __flip_bit(u32 msr, u8 bit, bool set)
  */
 int msr_set_bit(u32 msr, u8 bit)
 {
-	return __flip_bit(msr, bit, true);
+	return msr_flip_bit(msr, bit, true);
 }
 
 /**
@@ -109,7 +110,7 @@ int msr_set_bit(u32 msr, u8 bit)
  */
 int msr_clear_bit(u32 msr, u8 bit)
 {
-	return __flip_bit(msr, bit, false);
+	return msr_flip_bit(msr, bit, false);
 }
 
 #ifdef CONFIG_TRACEPOINTS
-- 
2.7.4