[PATCH v4 2/7] x86/msr: add wrmsrq_on_cpus helper

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@xxxxxxx>

The existing wrmsr_on_cpus() takes a per-cpu struct msr array, requiring
callers to allocate and populate per-cpu storage even when every CPU
receives the same value. This is unnecessary overhead for the common
case of writing a single uniform u64 to a per-CPU MSR across multiple
CPUs.

Add wrmsrq_on_cpus() which writes the same u64 value to the specified
MSR on all CPUs in the given cpumask.

Co-developed-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
---
 arch/x86/include/asm/msr.h |  5 +++++
 arch/x86/lib/msr-smp.c     | 20 ++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index 9c2ea29e12a9..f5f63b4115c8 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -260,6 +260,7 @@ int rdmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h);
 int wrmsr_on_cpu(unsigned int cpu, u32 msr_no, u32 l, u32 h);
 int rdmsrq_on_cpu(unsigned int cpu, u32 msr_no, u64 *q);
 int wrmsrq_on_cpu(unsigned int cpu, u32 msr_no, u64 q);
+void wrmsrq_on_cpus(const struct cpumask *mask, u32 msr_no, u64 q);
 void rdmsr_on_cpus(const struct cpumask *mask, u32 msr_no, struct msr __percpu *msrs);
 void wrmsr_on_cpus(const struct cpumask *mask, u32 msr_no, struct msr __percpu *msrs);
 int rdmsr_safe_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h);
@@ -289,6 +290,10 @@ static inline int wrmsrq_on_cpu(unsigned int cpu, u32 msr_no, u64 q)
 	wrmsrq(msr_no, q);
 	return 0;
 }
+static inline void wrmsrq_on_cpus(const struct cpumask *mask, u32 msr_no, u64 q)
+{
+	wrmsrq_on_cpu(0, msr_no, q);
+}
 static inline void rdmsr_on_cpus(const struct cpumask *m, u32 msr_no,
 				struct msr __percpu *msrs)
 {
diff --git a/arch/x86/lib/msr-smp.c b/arch/x86/lib/msr-smp.c
index b8f63419e6ae..d2c91c9bb47b 100644
--- a/arch/x86/lib/msr-smp.c
+++ b/arch/x86/lib/msr-smp.c
@@ -94,6 +94,26 @@ int wrmsrq_on_cpu(unsigned int cpu, u32 msr_no, u64 q)
 }
 EXPORT_SYMBOL(wrmsrq_on_cpu);
 
+void wrmsrq_on_cpus(const struct cpumask *mask, u32 msr_no, u64 q)
+{
+	struct msr_info rv;
+	int this_cpu;
+
+	memset(&rv, 0, sizeof(rv));
+
+	rv.msr_no = msr_no;
+	rv.reg.q = q;
+
+	this_cpu = get_cpu();
+
+	if (cpumask_test_cpu(this_cpu, mask))
+		__wrmsr_on_cpu(&rv);
+
+	smp_call_function_many(mask, __wrmsr_on_cpu, &rv, 1);
+	put_cpu();
+}
+EXPORT_SYMBOL(wrmsrq_on_cpus);
+
 static void __rwmsr_on_cpus(const struct cpumask *mask, u32 msr_no,
 			    struct msr __percpu *msrs,
 			    void (*msr_func) (void *info))
-- 
2.43.0