linux-kernel - [RFC PATCH v1 03/15] x86/msr: Simplify pmu_msr

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Message-ID: <20250331082251.3171276-4-xin@zytor.com>
Date: Mon, 31 Mar 2025 01:22:39 -0700
From: "Xin Li (Intel)" <xin@...or.com>
To: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-hyperv@...r.kernel.org, virtualization@...ts.linux.dev,
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Subject: [RFC PATCH v1 03/15] x86/msr: Simplify pmu_msr_{read,write}()

Remove calling native_{read,write}_msr{_safe}() in pmu_msr_{read,write}(),
and have them return false to let their caller to do that instead.

Refactor pmu_msr_write() to take the input MSR value in an u64 argument,
replacing the current dual u32 arguments.

Suggested-by: H. Peter Anvin (Intel) <hpa@...or.com>
Sign-off-by: Xin Li (Intel) <xin@...or.com>
---
 arch/x86/xen/enlighten_pv.c |  6 +++++-
 arch/x86/xen/pmu.c          | 27 ++++-----------------------
 arch/x86/xen/xen-ops.h      |  4 ++--
 3 files changed, 11 insertions(+), 26 deletions(-)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index dcc2041f8e61..2bfe57469ac3 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1133,6 +1133,8 @@ static void set_seg(unsigned int which, unsigned int low, unsigned int high,
 static void xen_do_write_msr(unsigned int msr, unsigned int low,
 			     unsigned int high, int *err)
 {
+	u64 val;
+
 	switch (msr) {
 	case MSR_FS_BASE:
 		set_seg(SEGBASE_FS, low, high, err);
@@ -1159,7 +1161,9 @@ static void xen_do_write_msr(unsigned int msr, unsigned int low,
 		break;
 
 	default:
-		if (!pmu_msr_write(msr, low, high, err)) {
+		val = (u64)high << 32 | low;
+
+		if (!pmu_msr_write(msr, val)) {
 			if (err)
 				*err = native_write_msr_safe(msr, low, high);
 			else
diff --git a/arch/x86/xen/pmu.c b/arch/x86/xen/pmu.c
index f06987b0efc3..1364cd3fb3ef 100644
--- a/arch/x86/xen/pmu.c
+++ b/arch/x86/xen/pmu.c
@@ -313,37 +313,18 @@ static bool pmu_msr_chk_emulated(unsigned int msr, uint64_t *val, bool is_read,
 	return true;
 }
 
-bool pmu_msr_read(unsigned int msr, uint64_t *val, int *err)
+bool pmu_msr_read(u32 msr, u64 *val, int *err)
 {
 	bool emulated;
 
-	if (!pmu_msr_chk_emulated(msr, val, true, &emulated))
-		return false;
-
-	if (!emulated) {
-		*val = err ? native_read_msr_safe(msr, err)
-			   : native_read_msr(msr);
-	}
-
-	return true;
+	return pmu_msr_chk_emulated(msr, val, true, &emulated) && emulated;
 }
 
-bool pmu_msr_write(unsigned int msr, uint32_t low, uint32_t high, int *err)
+bool pmu_msr_write(u32 msr, u64 val)
 {
-	uint64_t val = ((uint64_t)high << 32) | low;
 	bool emulated;
 
-	if (!pmu_msr_chk_emulated(msr, &val, false, &emulated))
-		return false;
-
-	if (!emulated) {
-		if (err)
-			*err = native_write_msr_safe(msr, low, high);
-		else
-			native_write_msr(msr, low, high);
-	}
-
-	return true;
+	return pmu_msr_chk_emulated(msr, &val, false, &emulated) && emulated;
 }
 
 static unsigned long long xen_amd_read_pmc(int counter)
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 63c13a2ccf55..4a0a1d73d8b8 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -274,8 +274,8 @@ void xen_pmu_finish(int cpu);
 static inline void xen_pmu_init(int cpu) {}
 static inline void xen_pmu_finish(int cpu) {}
 #endif
-bool pmu_msr_read(unsigned int msr, uint64_t *val, int *err);
-bool pmu_msr_write(unsigned int msr, uint32_t low, uint32_t high, int *err);
+bool pmu_msr_read(u32 msr, u64 *val, int *err);
+bool pmu_msr_write(u32 msr, u64 val);
 int pmu_apic_update(uint32_t reg);
 unsigned long long xen_read_pmc(int counter);
 
-- 
2.49.0