linux-kernel - [PATCH v1 37/40] x86/cacheinfo: Extract out cache self-snoop checks

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Message-ID: <20250304085152.51092-38-darwi@linutronix.de>
Date: Tue,  4 Mar 2025 09:51:48 +0100
From: "Ahmed S. Darwish" <darwi@...utronix.de>
To: Borislav Petkov <bp@...en8.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	John Ogness <john.ogness@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	x86@...nel.org,
	x86-cpuid@...ts.linux.dev,
	LKML <linux-kernel@...r.kernel.org>,
	"Ahmed S. Darwish" <darwi@...utronix.de>
Subject: [PATCH v1 37/40] x86/cacheinfo: Extract out cache self-snoop checks

The logic of not doing a cache flush if the CPU declares cache self
snooping support is repeated across the x86/cacheinfo code.  Extract it
into its own function.

Signed-off-by: Ahmed S. Darwish <darwi@...utronix.de>
---
 arch/x86/kernel/cpu/cacheinfo.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/cpu/cacheinfo.c b/arch/x86/kernel/cpu/cacheinfo.c
index 254c0b2e1d72..ac47d1b4f775 100644
--- a/arch/x86/kernel/cpu/cacheinfo.c
+++ b/arch/x86/kernel/cpu/cacheinfo.c
@@ -640,6 +640,17 @@ int populate_cache_leaves(unsigned int cpu)
 static unsigned long saved_cr4;
 static DEFINE_RAW_SPINLOCK(cache_disable_lock);
 
+/*
+ * Cache flushing is the most time-consuming step when programming the
+ * MTRRs.  On many Intel CPUs without known erratas, it can be skipped
+ * if the CPU declares cache self-snooping support.
+ */
+static void maybe_flush_caches(void)
+{
+	if (!static_cpu_has(X86_FEATURE_SELFSNOOP))
+		wbinvd();
+}
+
 void cache_disable(void) __acquires(cache_disable_lock)
 {
 	unsigned long cr0;
@@ -657,14 +668,7 @@ void cache_disable(void) __acquires(cache_disable_lock)
 	cr0 = read_cr0() | X86_CR0_CD;
 	write_cr0(cr0);
 
-	/*
-	 * Cache flushing is the most time-consuming step when programming
-	 * the MTRRs. Fortunately, as per the Intel Software Development
-	 * Manual, we can skip it if the processor supports cache self-
-	 * snooping.
-	 */
-	if (!static_cpu_has(X86_FEATURE_SELFSNOOP))
-		wbinvd();
+	maybe_flush_caches();
 
 	/* Save value of CR4 and clear Page Global Enable (bit 7) */
 	if (cpu_feature_enabled(X86_FEATURE_PGE)) {
@@ -679,9 +683,7 @@ void cache_disable(void) __acquires(cache_disable_lock)
 	if (cpu_feature_enabled(X86_FEATURE_MTRR))
 		mtrr_disable();
 
-	/* Again, only flush caches if we have to. */
-	if (!static_cpu_has(X86_FEATURE_SELFSNOOP))
-		wbinvd();
+	maybe_flush_caches();
 }
 
 void cache_enable(void) __releases(cache_disable_lock)
-- 
2.48.1