linux-kernel - [RFC PATCH v2 11/34] x86/msr: Remove calling native_{read,write}_msr{,_safe}() in pmu_msr

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Message-ID: <20250422082216.1954310-12-xin@zytor.com>
Date: Tue, 22 Apr 2025 01:21:52 -0700
From: "Xin Li (Intel)" <xin@...or.com>
To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-perf-users@...r.kernel.org, linux-hyperv@...r.kernel.org,
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Subject: [RFC PATCH v2 11/34] x86/msr: Remove calling native_{read,write}_msr{,_safe}() in pmu_msr_{read,write}()

hpa found that pmu_msr_write() is actually a completely pointless
function [1]: all it does is shuffle some arguments, then calls
pmu_msr_chk_emulated() and if it returns true AND the emulated flag
is clear then does *exactly the same thing* that the calling code
would have done if pmu_msr_write() itself had returned true.  And
pmu_msr_read() does the equivalent stupidity.

Remove the calls to native_{read,write}_msr{,_safe}() within
pmu_msr_{read,write}().  Instead reuse the existing calling code
that decides whether to call native_{read,write}_msr{,_safe}() based
on the return value from pmu_msr_{read,write}().  Consequently,
eliminate the need to pass an error pointer to pmu_msr_{read,write}().

While at it, refactor pmu_msr_write() to take the MSR value as a u64
argument, replacing the current dual u32 arguments, because the dual
u32 arguments were only used to call native_write_msr{,_safe}(), which
has now been removed.

[1]: https://lore.kernel.org/lkml/0ec48b84-d158-47c6-b14c-3563fd14bcc4@zytor.com/

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 9fbe187aff00..1418758b57ff 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1132,6 +1132,8 @@ 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);
@@ -1158,7 +1160,9 @@ 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 9c1682af620a..95caae97a394 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)
 {
 	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 u64 xen_amd_read_pmc(int counter)
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index dc886c3cc24d..a1875e10be31 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -271,8 +271,8 @@ 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);
+bool pmu_msr_write(u32 msr, u64 val);
 int pmu_apic_update(uint32_t reg);
 u64 xen_read_pmc(int counter);
 
-- 
2.49.0