linux-kernel - [PATCH v2 28/29] x86/cacheinfo: Introduce cpuid_amd_hygon_has_l3

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Message-ID: <20250317164745.4754-29-darwi@linutronix.de>
Date: Mon, 17 Mar 2025 17:47:44 +0100
From: "Ahmed S. Darwish" <darwi@...utronix.de>
To: Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Borislav Petkov <bp@...en8.de>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	John Ogness <john.ogness@...utronix.de>,
	x86@...nel.org,
	x86-cpuid@...ts.linux.dev,
	LKML <linux-kernel@...r.kernel.org>,
	"Ahmed S. Darwish" <darwi@...utronix.de>
Subject: [PATCH v2 28/29] x86/cacheinfo: Introduce cpuid_amd_hygon_has_l3_cache()

Multiple code paths at cacheinfo.c and amd_nb.c check for AMD/Hygon CPUs
L3 cache presensce by directly checking leaf 0x80000006 EDX output.

Extract that logic into its own function.  While at it, rework the
AMD/Hygon LLC topology ID caclculation comments for clarity.

Signed-off-by: Ahmed S. Darwish <darwi@...utronix.de>
---
 arch/x86/include/asm/cpuid/api.h |  9 +++++++++
 arch/x86/kernel/amd_nb.c         |  7 +++----
 arch/x86/kernel/cpu/cacheinfo.c  | 32 ++++++++++++++------------------
 3 files changed, 26 insertions(+), 22 deletions(-)

diff --git a/arch/x86/include/asm/cpuid/api.h b/arch/x86/include/asm/cpuid/api.h
index 4d1da9cc8b6f..d2ca5d813523 100644
--- a/arch/x86/include/asm/cpuid/api.h
+++ b/arch/x86/include/asm/cpuid/api.h
@@ -205,4 +205,13 @@ static inline uint32_t hypervisor_cpuid_base(const char *sig, uint32_t leaves)
 	return 0;
 }
 
+/*
+ * CPUID(0x80000006) parsing helpers
+ */
+
+static inline bool cpuid_amd_hygon_has_l3_cache(void)
+{
+	return cpuid_edx(0x80000006);
+}
+
 #endif /* _ASM_X86_CPUID_API_H */
diff --git a/arch/x86/kernel/amd_nb.c b/arch/x86/kernel/amd_nb.c
index bac8d3b6f12b..6d51689ffbf2 100644
--- a/arch/x86/kernel/amd_nb.c
+++ b/arch/x86/kernel/amd_nb.c
@@ -13,7 +13,9 @@
 #include <linux/export.h>
 #include <linux/spinlock.h>
 #include <linux/pci_ids.h>
+
 #include <asm/amd_nb.h>
+#include <asm/cpuid.h>
 
 static u32 *flush_words;
 
@@ -92,10 +94,7 @@ static int amd_cache_northbridges(void)
 	if (amd_gart_present())
 		amd_northbridges.flags |= AMD_NB_GART;
 
-	/*
-	 * Check for L3 cache presence.
-	 */
-	if (!cpuid_edx(0x80000006))
+	if (!cpuid_amd_hygon_has_l3_cache())
 		return 0;
 
 	/*
diff --git a/arch/x86/kernel/cpu/cacheinfo.c b/arch/x86/kernel/cpu/cacheinfo.c
index 38683e86fab4..397c3dbc5851 100644
--- a/arch/x86/kernel/cpu/cacheinfo.c
+++ b/arch/x86/kernel/cpu/cacheinfo.c
@@ -278,29 +278,29 @@ static int find_num_cache_leaves(struct cpuinfo_x86 *c)
 	return i;
 }
 
+/*
+ * AMD/Hygon CPUs may have multiple LLCs if L3 caches exist.
+ */
+
 void cacheinfo_amd_init_llc_id(struct cpuinfo_x86 *c, u16 die_id)
 {
-	/*
-	 * We may have multiple LLCs if L3 caches exist, so check if we
-	 * have an L3 cache by looking at the L3 cache CPUID leaf.
-	 */
-	if (!cpuid_edx(0x80000006))
+	if (!cpuid_amd_hygon_has_l3_cache())
 		return;
 
 	if (c->x86 < 0x17) {
-		/* LLC is at the node level. */
+		/* Pre-Zen: LLC is at the node level */
 		c->topo.llc_id = die_id;
 	} else if (c->x86 == 0x17 && c->x86_model <= 0x1F) {
 		/*
-		 * LLC is at the core complex level.
-		 * Core complex ID is ApicId[3] for these processors.
+		 * Family 17h up to 1F models: LLC is at the core
+		 * complex level.  Core complex ID is ApicId[3].
 		 */
 		c->topo.llc_id = c->topo.apicid >> 3;
 	} else {
 		/*
-		 * LLC ID is calculated from the number of threads sharing the
-		 * cache.
-		 * */
+		 * Newer families: LLC ID is calculated from the number
+		 * of threads sharing the L3 cache.
+		 */
 		u32 eax, ebx, ecx, edx, num_sharing_cache = 0;
 		u32 llc_index = find_num_cache_leaves(c) - 1;
 
@@ -318,16 +318,12 @@ void cacheinfo_amd_init_llc_id(struct cpuinfo_x86 *c, u16 die_id)
 
 void cacheinfo_hygon_init_llc_id(struct cpuinfo_x86 *c)
 {
-	/*
-	 * We may have multiple LLCs if L3 caches exist, so check if we
-	 * have an L3 cache by looking at the L3 cache CPUID leaf.
-	 */
-	if (!cpuid_edx(0x80000006))
+	if (!cpuid_amd_hygon_has_l3_cache())
 		return;
 
 	/*
-	 * LLC is at the core complex level.
-	 * Core complex ID is ApicId[3] for these processors.
+	 * Hygons are similar to AMD Family 17h up to 1F models: LLC is
+	 * at the core complex level.  Core complex ID is ApicId[3].
 	 */
 	c->topo.llc_id = c->topo.apicid >> 3;
 }
-- 
2.48.1