linux-kernel - [PATCH v5 1/2] x86, lib: Add WBNOINVD helper functions

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Message-ID: <20250123002422.1632517-2-kevinloughlin@google.com>
Date: Thu, 23 Jan 2025 00:24:21 +0000
From: Kevin Loughlin <kevinloughlin@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, seanjc@...gle.com, 
	pbonzini@...hat.com, kevinloughlin@...gle.com, 
	kirill.shutemov@...ux.intel.com, kai.huang@...el.com, ubizjak@...il.com, 
	jgross@...e.com, kvm@...r.kernel.org, thomas.lendacky@....com, 
	pgonda@...gle.com, sidtelang@...gle.com, mizhang@...gle.com, 
	rientjes@...gle.com, manalinandan@...gle.com, szy0127@...u.edu.cn
Subject: [PATCH v5 1/2] x86, lib: Add WBNOINVD helper functions

In line with WBINVD usage, add WBONINVD helper functions. For the
wbnoinvd() helper, fall back to WBINVD if X86_FEATURE_WBNOINVD is not
present.

Signed-off-by: Kevin Loughlin <kevinloughlin@...gle.com>
---
 arch/x86/include/asm/smp.h           |  7 +++++++
 arch/x86/include/asm/special_insns.h | 20 +++++++++++++++++++-
 arch/x86/lib/cache-smp.c             | 12 ++++++++++++
 3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index ca073f40698f..ecf93a243b83 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -112,6 +112,7 @@ void native_play_dead(void);
 void play_dead_common(void);
 void wbinvd_on_cpu(int cpu);
 int wbinvd_on_all_cpus(void);
+int wbnoinvd_on_all_cpus(void);
 
 void smp_kick_mwait_play_dead(void);
 
@@ -160,6 +161,12 @@ static inline int wbinvd_on_all_cpus(void)
 	return 0;
 }
 
+static inline int wbnoinvd_on_all_cpus(void)
+{
+	wbnoinvd();
+	return 0;
+}
+
 static inline struct cpumask *cpu_llc_shared_mask(int cpu)
 {
 	return (struct cpumask *)cpumask_of(0);
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index 03e7c2d49559..fb3ddb2ddea9 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -117,7 +117,25 @@ static inline void wrpkru(u32 pkru)
 
 static __always_inline void wbinvd(void)
 {
-	asm volatile("wbinvd": : :"memory");
+	asm volatile("wbinvd" : : : "memory");
+}
+
+/*
+ * Cheaper version of wbinvd(). Call when caches
+ * need to be written back but not invalidated.
+ */
+static __always_inline void wbnoinvd(void)
+{
+	/*
+	 * WBNOINVD is encoded as 0xf3 0x0f 0x09. Making this
+	 * encoding explicit ensures compatibility with older versions of
+	 * binutils, which may not know about WBNOINVD.
+	 *
+	 * If WBNOINVD is unavailable, fall back to the compatible but
+	 * more destructive WBINVD (which still writes the caches back
+	 * but also invalidates them).
+	 */
+	alternative("wbinvd", ".byte 0xf3,0x0f,0x09", X86_FEATURE_WBNOINVD);
 }
 
 static inline unsigned long __read_cr4(void)
diff --git a/arch/x86/lib/cache-smp.c b/arch/x86/lib/cache-smp.c
index 7af743bd3b13..7ac5cca53031 100644
--- a/arch/x86/lib/cache-smp.c
+++ b/arch/x86/lib/cache-smp.c
@@ -20,3 +20,15 @@ int wbinvd_on_all_cpus(void)
 	return 0;
 }
 EXPORT_SYMBOL(wbinvd_on_all_cpus);
+
+static void __wbnoinvd(void *dummy)
+{
+	wbnoinvd();
+}
+
+int wbnoinvd_on_all_cpus(void)
+{
+	on_each_cpu(__wbnoinvd, NULL, 1);
+	return 0;
+}
+EXPORT_SYMBOL(wbnoinvd_on_all_cpus);
-- 
2.48.1.262.g85cc9f2d1e-goog