[tip: x86/cpu] x86/cacheinfo: Introduce cpuid_amd_hygon_has_l3_cache()

[tip-bot2 for Ahmed S. Darwish]

The following commit has been merged into the x86/cpu branch of tip:

Commit-ID:     6c963c42fc19d7c9ae9582ab75c3476d1752d979
Gitweb:        https://git.kernel.org/tip/6c963c42fc19d7c9ae9582ab75c3476d1752d979
Author:        Ahmed S. Darwish <darwi@xxxxxxxxxxxxx>
AuthorDate:    Mon, 24 Mar 2025 14:33:23 +01:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 25 Mar 2025 10:23:30 +01:00

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@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250324133324.23458-29-darwi@xxxxxxxxxxxxx
---
 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 9c180c9..bf75c62 100644
--- a/arch/x86/include/asm/cpuid/api.h
+++ b/arch/x86/include/asm/cpuid/api.h
@@ -207,4 +207,13 @@ static inline u32 hypervisor_cpuid_base(const char *sig, u32 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 6d12a9b..5a8cc48 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;
 
@@ -91,10 +93,7 @@ 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 e0d531e..7158757 100644
--- a/arch/x86/kernel/cpu/cacheinfo.c
+++ b/arch/x86/kernel/cpu/cacheinfo.c
@@ -281,29 +281,29 @@ 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;
 
@@ -321,16 +321,12 @@ 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;
 }