linux-kernel - [PATCH 1/2] arch/x86: Set L2 Cache ID on AMD processors

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Date:   Mon, 10 Apr 2023 22:05:26 +0530
From:   K Prateek Nayak <kprateek.nayak@....com>
To:     <linux-kernel@...r.kernel.org>
CC:     <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <dave.hansen@...ux.intel.com>, <hpa@...or.com>, <corbet@....net>,
        <jgross@...e.com>, <andrew.cooper3@...rix.com>,
        <peterz@...radead.org>, <Jason@...c4.com>,
        <thomas.lendacky@....com>, <puwen@...on.cn>, <x86@...nel.org>,
        <linux-doc@...r.kernel.org>
Subject: [PATCH 1/2] arch/x86: Set L2 Cache ID on AMD processors

On AMD processors supporting X86_FEATURE_TOPOEXT set the l2c_id using the
Extended APIC ID and the Cache Properties CPUID.

Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
---
 arch/x86/include/asm/cacheinfo.h |  1 +
 arch/x86/kernel/cpu/amd.c        |  1 +
 arch/x86/kernel/cpu/cacheinfo.c  | 36 ++++++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/arch/x86/include/asm/cacheinfo.h b/arch/x86/include/asm/cacheinfo.h
index ce9685fc78d8..5e472fc364c8 100644
--- a/arch/x86/include/asm/cacheinfo.h
+++ b/arch/x86/include/asm/cacheinfo.h
@@ -7,6 +7,7 @@ extern unsigned int memory_caching_control;
 #define CACHE_MTRR 0x01
 #define CACHE_PAT  0x02
 
+void cacheinfo_amd_init_l2c_id(struct cpuinfo_x86 *c, int cpu);
 void cacheinfo_amd_init_llc_id(struct cpuinfo_x86 *c, int cpu);
 void cacheinfo_hygon_init_llc_id(struct cpuinfo_x86 *c, int cpu);
 
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index f769d6d08b43..e68d31231666 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -358,6 +358,7 @@ static void amd_get_topology(struct cpuinfo_x86 *c)
 		if (!err)
 			c->x86_coreid_bits = get_count_order(c->x86_max_cores);
 
+		cacheinfo_amd_init_l2c_id(c, cpu);
 		cacheinfo_amd_init_llc_id(c, cpu);
 
 	} else if (cpu_has(c, X86_FEATURE_NODEID_MSR)) {
diff --git a/arch/x86/kernel/cpu/cacheinfo.c b/arch/x86/kernel/cpu/cacheinfo.c
index f4e5aa27eec6..0baf2d9b1595 100644
--- a/arch/x86/kernel/cpu/cacheinfo.c
+++ b/arch/x86/kernel/cpu/cacheinfo.c
@@ -659,6 +659,42 @@ static int find_num_cache_leaves(struct cpuinfo_x86 *c)
 	return i;
 }
 
+void cacheinfo_amd_init_l2c_id(struct cpuinfo_x86 *c, int cpu)
+{
+	u32 eax, ebx, ecx, edx, num_sharing_cache;
+	int i = 0, bits;
+
+	/* Check if L2 cache identifiers exists. */
+	if (!cpuid_ecx(0x80000006))
+		return;
+
+	while (true) {
+		u32 level;
+
+		cpuid_count(0x8000001d, i, &eax, &ebx, &ecx, &edx);
+		if (!eax)
+			return;
+
+		/*
+		 * Check if the current leaf is for L2 cache using
+		 * eax[7:5] used to describe the cache level.
+		 */
+		level = (eax >> 5) & 0x7;
+		if (level == 2)
+			break;
+
+		++i;
+	}
+
+	/*
+	 * L2 ID is calculated from the number of threads
+	 * sharing the L2 cache.
+	 */
+	num_sharing_cache = ((eax >> 14) & 0xfff) + 1;
+	bits = get_count_order(num_sharing_cache);
+	per_cpu(cpu_l2c_id, cpu) = c->apicid >> bits;
+}
+
 void cacheinfo_amd_init_llc_id(struct cpuinfo_x86 *c, int cpu)
 {
 	/*
-- 
2.34.1