linux-kernel - [PATCH v2 4/8] x86, lib: Add WBNOINVD helper functions

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Message-ID: <20250516212833.2544737-5-seanjc@google.com>
Date: Fri, 16 May 2025 14:28:29 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, Zheyun Shen <szy0127@...u.edu.cn>, 
	Tom Lendacky <thomas.lendacky@....com>, Kevin Loughlin <kevinloughlin@...gle.com>, 
	Kai Huang <kai.huang@...el.com>, Mingwei Zhang <mizhang@...gle.com>
Subject: [PATCH v2 4/8] x86, lib: Add WBNOINVD helper functions

From: Kevin Loughlin <kevinloughlin@...gle.com>

In line with WBINVD usage, add WBONINVD helper functions.  Fall back to
WBINVD (via alternative()) if WBNOINVD isn't supported, as WBINVD provides
a superset of functionality, just more slowly.

Note, alternative() ensures compatibility with early boot code as needed.

Signed-off-by: Kevin Loughlin <kevinloughlin@...gle.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
[sean: massage changelog and comments, use ASM_WBNOINVD and _ASM_BYTES]
Reviewed-by: Kai Huang <kai.huang@...el.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/smp.h           |  6 ++++++
 arch/x86/include/asm/special_insns.h | 19 ++++++++++++++++++-
 arch/x86/lib/cache-smp.c             | 11 +++++++++++
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index 028f126018c9..e08f1ae25401 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -113,6 +113,7 @@ void native_play_dead(void);
 void play_dead_common(void);
 void wbinvd_on_cpu(int cpu);
 void wbinvd_on_all_cpus(void);
+void wbnoinvd_on_all_cpus(void);
 
 void smp_kick_mwait_play_dead(void);
 void __noreturn mwait_play_dead(unsigned int eax_hint);
@@ -153,6 +154,11 @@ static inline void wbinvd_on_all_cpus(void)
 	wbinvd();
 }
 
+static inline void wbnoinvd_on_all_cpus(void)
+{
+	wbnoinvd();
+}
+
 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 6266d6b9e0b8..46b3961e3e4b 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -117,7 +117,24 @@ static inline void wrpkru(u32 pkru)
 
 static __always_inline void wbinvd(void)
 {
-	asm volatile("wbinvd": : :"memory");
+	asm volatile("wbinvd" : : : "memory");
+}
+
+/* Instruction encoding provided for binutils backwards compatibility. */
+#define ASM_WBNOINVD _ASM_BYTES(0xf3,0x0f,0x09)
+
+/*
+ * Cheaper version of wbinvd(). Call when caches need to be written back but
+ * not invalidated.
+ */
+static __always_inline void wbnoinvd(void)
+{
+	/*
+	 * 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", ASM_WBNOINVD, 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 079c3f3cd32c..1789db5d8825 100644
--- a/arch/x86/lib/cache-smp.c
+++ b/arch/x86/lib/cache-smp.c
@@ -19,3 +19,14 @@ void wbinvd_on_all_cpus(void)
 	on_each_cpu(__wbinvd, NULL, 1);
 }
 EXPORT_SYMBOL(wbinvd_on_all_cpus);
+
+static void __wbnoinvd(void *dummy)
+{
+	wbnoinvd();
+}
+
+void wbnoinvd_on_all_cpus(void)
+{
+	on_each_cpu(__wbnoinvd, NULL, 1);
+}
+EXPORT_SYMBOL(wbnoinvd_on_all_cpus);
-- 
2.49.0.1112.g889b7c5bd8-goog