[RFC][PATCH 21/34] x86/cpu: Consolidate CLFLUSH size setting.

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

Right now, cpu_detect() establishes ->x86_clflush_size on each CPU
that.  supports CLFLUSH.  As you might have guessed, that per-cpu
value is no longer used.

Move the setting to get_cpu_address_sizes() which is only called
on the boot CPU.  Consolidate all of the ->x86_clflush_size logic
into a single helper.

This removes the (cap0 & (1<<19) aka X86_FEATURE_CLFLUSH check before
reading the CLFLUSH size out of CPUID[1].  Those bits are presumably
either 0 or have actual data about CLFLUSH in them.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---

 b/arch/x86/kernel/cpu/common.c |   35 ++++++++++++++++++++++++-----------
 1 file changed, 24 insertions(+), 11 deletions(-)

diff -puN arch/x86/kernel/cpu/common.c~later-clflush_size-detect arch/x86/kernel/cpu/common.c
--- a/arch/x86/kernel/cpu/common.c~later-clflush_size-detect	2024-02-22 10:08:58.728856457 -0800
+++ b/arch/x86/kernel/cpu/common.c	2024-02-22 10:08:58.732856614 -0800
@@ -935,6 +935,27 @@ static void get_cpu_vendor(struct cpuinf
 	this_cpu = &default_cpu;
 }
 
+static u16 detect_clflush_size(struct cpuinfo_x86 *c)
+{
+	u16 clflush_size = 0;
+
+	if (c->cpuid_level >= 0x00000001) {
+		u32 eax, ebx, ecx, edx;
+
+		cpuid(0x00000001, &eax, &ebx, &ecx, &edx);
+
+		clflush_size = ((ebx >> 8) & 0xff) * 8;
+	}
+
+	if (clflush_size)
+		return clflush_size;
+
+	/* Return some mostly sane defaults: */
+	if (IS_ENABLED(CONFIG_X86_64))
+		return 64;
+	return 32;
+}
+
 void cpu_detect(struct cpuinfo_x86 *c)
 {
 	/* Get vendor name */
@@ -952,11 +973,6 @@ void cpu_detect(struct cpuinfo_x86 *c)
 		c->x86		= x86_family(tfms);
 		c->x86_model	= x86_model(tfms);
 		c->x86_stepping	= x86_stepping(tfms);
-
-		if (cap0 & (1<<19)) {
-			if (c == &boot_cpu_data)
-				c->x86_clflush_size = ((misc >> 8) & 0xff) * 8;
-		}
 	}
 }
 
@@ -1111,17 +1127,17 @@ void get_cpu_address_sizes(struct cpuinf
 		if (IS_ENABLED(CONFIG_X86_64)) {
 			x86_config.phys_bits = 36;
 			x86_config.virt_bits = 48;
-			c->x86_clflush_size = 64;
 		} else {
 			x86_config.phys_bits = 32;
 			x86_config.virt_bits = 32;
-			c->x86_clflush_size = 32;
 
 			if (cpu_has(c, X86_FEATURE_PAE) ||
 			    cpu_has(c, X86_FEATURE_PSE36))
 				x86_config.phys_bits = 36;
 		}
 	}
+	c->x86_clflush_size = detect_clflush_size(c);
+
 	c->x86_cache_bits = x86_config.phys_bits;
 
 	c->x86_cache_alignment = x86_clflush_size();
@@ -1827,11 +1843,8 @@ static void identify_cpu(struct cpuinfo_
 	c->topo.cu_id = 0xff;
 	c->topo.llc_id = BAD_APICID;
 	c->topo.l2c_id = BAD_APICID;
-#ifdef CONFIG_X86_64
-	c->x86_clflush_size = 64;
-#else
+#ifndef CONFIG_X86_64
 	c->cpuid_level = -1;	/* CPUID not detected */
-	c->x86_clflush_size = 32;
 #endif
 	memset(&c->x86_capability, 0, sizeof(c->x86_capability));
 #ifdef CONFIG_X86_VMX_FEATURE_NAMES
_