[PATCH v2 0/3] x86/topology: Add support for Low Power cpu_type

[PATCH v2 0/3] x86/topology: Add support for Low Power cpu_type

[Vishal Badole]

This series extends the x86 topology cpu_type classification to support
a Low Power core type, in addition to the existing Performance and
Efficiency types.

AMD heterogeneous parts report the core type via CPUID Fn0x80000026
EBX[31:28] (Extended CPU Topology, Core Type). Value 2 identifies a
low-power core. Distinguishing it from a regular efficiency core
matters for:

  - user space exposure via /sys/kernel/debug/x86/topo/cpus/*, which
    today reports cpu_type "unknown" for low-power cores

  - amd_get_boost_ratio_numerator(): on every
    X86_FEATURE_AMD_HTR_CORES-capable AMD/Hygon part, low-power cores
    must scale by amd_get_highest_perf() rather than the fixed
    CPPC_HIGHEST_PERF_PERFORMANCE ceiling, matching the existing
    efficiency-core path

During the v1 review, Sashiko flagged a pre-existing issue in how
x86_match_cpu() handles vendor CPU types. v2 therefore starts with a
preparatory patch from Borislav that switches matching to the kernel's
vendor-agnostic TOPO_CPU_TYPE_* enum; see its commit message for
details. The Low Power support is then added on top.

The series is structured as:

  1/3 Map the vendor (Intel/AMD) hardware core type to the
      vendor-agnostic enum x86_topology_cpu_type at enumeration and
      match against it. See the patch's commit message for details.

  2/3 Replace the bare 0/1 in get_topology_cpu_type() with named
      enum amd_cpu_type constants, mirroring the existing Intel side.
      No functional change.

  3/3 Add TOPO_CPU_TYPE_LOW_POWER, wire it through
      get_topology_cpu_type(), get_topology_cpu_type_name() and the
      switch in amd_get_boost_ratio_numerator() so allmodconfig builds
      cleanly under -Werror=switch.

Changes in v2:
  - New preparatory patch 1/3 from Borislav Petkov switching
    x86_match_cpu() to the vendor-agnostic TOPO_CPU_TYPE_* enum; see
    its commit message for the rationale. (Thomas Gleixner,
    Borislav Petkov)
  - No change to the Low Power translation logic itself; patches 2/3
    and 3/3 are the v1 patches rebased on top of the new 1/3.

v1: https://lore.kernel.org/all/20260629094349.533301-1-Vishal.Badole@amd.com

Borislav Petkov (AMD) (1):
  x86/topo: Map vendor CPU types to generic Linux such types

Vishal Badole (2):
  x86/topology: Name the AMD core-type values
  x86/topology: Add TOPO_CPU_TYPE_LOW_POWER

 arch/x86/include/asm/processor.h      | 19 +++++++++++++----
 arch/x86/include/asm/topology.h       |  9 ++++----
 arch/x86/kernel/acpi/cppc.c           |  7 ++++---
 arch/x86/kernel/cpu/match.c           | 30 +--------------------------
 arch/x86/kernel/cpu/topology.h        |  1 +
 arch/x86/kernel/cpu/topology_amd.c    |  6 ++++--
 arch/x86/kernel/cpu/topology_common.c | 15 ++++++++++----
 7 files changed, 40 insertions(+), 47 deletions(-)

-- 
2.34.1

[PATCH v2 1/3] x86/topo: Map vendor CPU types to generic Linux such types

[Vishal Badole]

From: "Borislav Petkov (AMD)" <bp@alien8.de>

Sashiko reported¹ that a confusion could ensue if a vendor-specific CPU
type 0 (performance) gets attempted to be used in a x86_cpu_id match
table. The current logic treats 0 as the wildcard X86_CPU_TYPE_ANY and
such a thing would end up matching the wrong CPUs.

This is all backwards because we started using the vendor-specific CPU
type number instead of using a Linux-defined, generic CPU type which
is agnostic.

Convert the current logic to it before users start appearing.

  ¹https://sashiko.dev/#/patchset/20260629094349.533301-1-Vishal.Badole%40amd.com

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Vishal Badole <Vishal.Badole@amd.com>
---
 arch/x86/include/asm/processor.h      | 18 ++++++++++++----
 arch/x86/include/asm/topology.h       |  7 -------
 arch/x86/kernel/acpi/cppc.c           |  4 ++--
 arch/x86/kernel/cpu/match.c           | 30 +--------------------------
 arch/x86/kernel/cpu/topology.h        |  1 +
 arch/x86/kernel/cpu/topology_amd.c    |  6 ++++--
 arch/x86/kernel/cpu/topology_common.c |  8 +++++--
 7 files changed, 28 insertions(+), 46 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 87b1d4c0727e..fc0350fe8f5e 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -68,9 +68,13 @@ extern u16 __read_mostly tlb_lld_2m;
 extern u16 __read_mostly tlb_lld_4m;
 extern u16 __read_mostly tlb_lld_1g;
 
-/*
- * CPU type and hardware bug flags. Kept separately for each CPU.
- */
+enum x86_topology_cpu_type {
+	/* X86_CPU_TYPE_ANY */
+	TOPO_CPU_TYPE_ANY = 0,
+	TOPO_CPU_TYPE_PERFORMANCE,
+	TOPO_CPU_TYPE_EFFICIENCY,
+	TOPO_CPU_TYPE_UNKNOWN,
+};
 
 struct cpuinfo_topology {
 	// Real APIC ID read from the local APIC
@@ -104,7 +108,7 @@ struct cpuinfo_topology {
 
 	// Hardware defined CPU-type
 	union {
-		u32		cpu_type;
+		u32		hw_cpu_type;
 		struct {
 			// CPUID.1A.EAX[23-0]
 			u32	intel_native_model_id	:24;
@@ -119,8 +123,14 @@ struct cpuinfo_topology {
 				amd_type		:4;
 		};
 	};
+
+	// Linux vendor-agnostic CPU type
+	enum x86_topology_cpu_type cpu_type;
 };
 
+/*
+ * CPU type and hardware bug flags. Kept separately for each CPU.
+ */
 struct cpuinfo_x86 {
 	union {
 		/*
diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
index 8fb61d2465eb..ef76ba674f1b 100644
--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -114,12 +114,6 @@ enum x86_topology_domains {
 	TOPO_MAX_DOMAIN,
 };
 
-enum x86_topology_cpu_type {
-	TOPO_CPU_TYPE_PERFORMANCE,
-	TOPO_CPU_TYPE_EFFICIENCY,
-	TOPO_CPU_TYPE_UNKNOWN,
-};
-
 struct x86_topology_system {
 	unsigned int	dom_shifts[TOPO_MAX_DOMAIN];
 	unsigned int	dom_size[TOPO_MAX_DOMAIN];
@@ -160,7 +154,6 @@ extern unsigned int __num_nodes_per_package;
 struct cpuinfo_x86;
 
 const char *get_topology_cpu_type_name(struct cpuinfo_x86 *c);
-enum x86_topology_cpu_type get_topology_cpu_type(struct cpuinfo_x86 *c);
 
 static inline unsigned int topology_max_packages(void)
 {
diff --git a/arch/x86/kernel/acpi/cppc.c b/arch/x86/kernel/acpi/cppc.c
index be4c5e9e5ff6..b8f5dd0a8117 100644
--- a/arch/x86/kernel/acpi/cppc.c
+++ b/arch/x86/kernel/acpi/cppc.c
@@ -241,7 +241,6 @@ EXPORT_SYMBOL_GPL(amd_detect_prefcore);
  */
 int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator)
 {
-	enum x86_topology_cpu_type core_type = get_topology_cpu_type(&cpu_data(cpu));
 	bool prefcore;
 	int ret;
 	u32 tmp;
@@ -273,8 +272,9 @@ int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator)
 
 	/* detect if running on heterogeneous design */
 	if (cpu_feature_enabled(X86_FEATURE_AMD_HTR_CORES)) {
-		switch (core_type) {
+		switch (cpu_data(cpu).topo.cpu_type) {
 		case TOPO_CPU_TYPE_UNKNOWN:
+		case TOPO_CPU_TYPE_ANY:
 			pr_warn("Undefined core type found for cpu %d\n", cpu);
 			break;
 		case TOPO_CPU_TYPE_PERFORMANCE:
diff --git a/arch/x86/kernel/cpu/match.c b/arch/x86/kernel/cpu/match.c
index 4604802692da..7ab077f0cc66 100644
--- a/arch/x86/kernel/cpu/match.c
+++ b/arch/x86/kernel/cpu/match.c
@@ -5,34 +5,6 @@
 #include <linux/export.h>
 #include <linux/slab.h>
 
-/**
- * x86_match_vendor_cpu_type - helper function to match the hardware defined
- *                             cpu-type for a single entry in the x86_cpu_id
- *                             table. Note, this function does not match the
- *                             generic cpu-types TOPO_CPU_TYPE_EFFICIENCY and
- *                             TOPO_CPU_TYPE_PERFORMANCE.
- * @c: Pointer to the cpuinfo_x86 structure of the CPU to match.
- * @m: Pointer to the x86_cpu_id entry to match against.
- *
- * Return: true if the cpu-type matches, false otherwise.
- */
-static bool x86_match_vendor_cpu_type(struct cpuinfo_x86 *c, const struct x86_cpu_id *m)
-{
-	if (m->type == X86_CPU_TYPE_ANY)
-		return true;
-
-	/* Hybrid CPUs are special, they are assumed to match all cpu-types */
-	if (cpu_feature_enabled(X86_FEATURE_HYBRID_CPU))
-		return true;
-
-	if (c->x86_vendor == X86_VENDOR_INTEL)
-		return m->type == c->topo.intel_type;
-	if (c->x86_vendor == X86_VENDOR_AMD)
-		return m->type == c->topo.amd_type;
-
-	return false;
-}
-
 /**
  * x86_match_cpu - match current CPU against an array of x86_cpu_ids
  * @match: Pointer to array of x86_cpu_ids. Last entry terminated with
@@ -81,7 +53,7 @@ const struct x86_cpu_id *x86_match_cpu(const struct x86_cpu_id *match)
 			continue;
 		if (m->feature != X86_FEATURE_ANY && !cpu_has(c, m->feature))
 			continue;
-		if (!x86_match_vendor_cpu_type(c, m))
+		if (m->type != X86_CPU_TYPE_ANY && c->topo.cpu_type != m->type)
 			continue;
 		return m;
 	}
diff --git a/arch/x86/kernel/cpu/topology.h b/arch/x86/kernel/cpu/topology.h
index 37326297f80c..74e02bacd854 100644
--- a/arch/x86/kernel/cpu/topology.h
+++ b/arch/x86/kernel/cpu/topology.h
@@ -22,6 +22,7 @@ void topology_set_dom(struct topo_scan *tscan, enum x86_topology_domains dom,
 bool cpu_parse_topology_ext(struct topo_scan *tscan);
 void cpu_parse_topology_amd(struct topo_scan *tscan);
 void cpu_topology_fixup_amd(struct topo_scan *tscan);
+enum x86_topology_cpu_type get_topology_cpu_type(struct cpuinfo_x86 *c);
 
 static inline u32 topo_shift_apicid(u32 apicid, enum x86_topology_domains dom)
 {
diff --git a/arch/x86/kernel/cpu/topology_amd.c b/arch/x86/kernel/cpu/topology_amd.c
index da080d732e10..c5a6944df86a 100644
--- a/arch/x86/kernel/cpu/topology_amd.c
+++ b/arch/x86/kernel/cpu/topology_amd.c
@@ -177,8 +177,10 @@ static void topoext_fixup(struct topo_scan *tscan)
 
 static void parse_topology_amd(struct topo_scan *tscan)
 {
-	if (cpu_feature_enabled(X86_FEATURE_AMD_HTR_CORES))
-		tscan->c->topo.cpu_type = cpuid_ebx(0x80000026);
+	if (cpu_feature_enabled(X86_FEATURE_AMD_HTR_CORES)) {
+		tscan->c->topo.hw_cpu_type = cpuid_ebx(0x80000026);
+		tscan->c->topo.cpu_type    = get_topology_cpu_type(tscan->c);
+	}
 
 	/*
 	 * Try to get SMT, CORE, TILE, and DIE shifts from extended
diff --git a/arch/x86/kernel/cpu/topology_common.c b/arch/x86/kernel/cpu/topology_common.c
index cf7513416b70..b9d025f3373a 100644
--- a/arch/x86/kernel/cpu/topology_common.c
+++ b/arch/x86/kernel/cpu/topology_common.c
@@ -168,8 +168,12 @@ static void parse_topology(struct topo_scan *tscan, bool early)
 	case X86_VENDOR_INTEL:
 		if (!IS_ENABLED(CONFIG_CPU_SUP_INTEL) || !cpu_parse_topology_ext(tscan))
 			parse_legacy(tscan);
-		if (c->cpuid_level >= 0x1a)
-			c->topo.cpu_type = cpuid_eax(0x1a);
+
+		if (c->cpuid_level >= 0x1a) {
+			c->topo.hw_cpu_type = cpuid_eax(0x1a);
+			c->topo.cpu_type    = get_topology_cpu_type(c);
+		}
+
 		break;
 	}
 }
-- 
2.34.1

[PATCH v2 2/3] x86/topology: Name the AMD core-type values

[Vishal Badole]

Replace the bare 0/1 in get_topology_cpu_type() with named constants
that mirror what the AMD APM publishes for CPUID Fn0x80000026
EBX[31:28] (Extended CPU Topology, Core Type):

  0 - Performance core
  1 - Efficient core
  2 - Low-power core (used by a follow-up)

No functional change.

Suggested-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Vishal Badole <Vishal.Badole@amd.com>
---
 arch/x86/include/asm/topology.h       | 6 ++++++
 arch/x86/kernel/cpu/topology_common.c | 4 ++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
index ef76ba674f1b..1825691af941 100644
--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -114,6 +114,12 @@ enum x86_topology_domains {
 	TOPO_MAX_DOMAIN,
 };
 
+enum amd_cpu_type {
+	AMD_CPU_TYPE_PERFORMANCE	= 0,
+	AMD_CPU_TYPE_EFFICIENCY		= 1,
+	AMD_CPU_TYPE_LOW_POWER		= 2,
+};
+
 struct x86_topology_system {
 	unsigned int	dom_shifts[TOPO_MAX_DOMAIN];
 	unsigned int	dom_size[TOPO_MAX_DOMAIN];
diff --git a/arch/x86/kernel/cpu/topology_common.c b/arch/x86/kernel/cpu/topology_common.c
index b9d025f3373a..71b6c33afe0b 100644
--- a/arch/x86/kernel/cpu/topology_common.c
+++ b/arch/x86/kernel/cpu/topology_common.c
@@ -42,8 +42,8 @@ enum x86_topology_cpu_type get_topology_cpu_type(struct cpuinfo_x86 *c)
 	}
 	if (c->x86_vendor == X86_VENDOR_AMD) {
 		switch (c->topo.amd_type) {
-		case 0:	return TOPO_CPU_TYPE_PERFORMANCE;
-		case 1:	return TOPO_CPU_TYPE_EFFICIENCY;
+		case AMD_CPU_TYPE_PERFORMANCE:	return TOPO_CPU_TYPE_PERFORMANCE;
+		case AMD_CPU_TYPE_EFFICIENCY:	return TOPO_CPU_TYPE_EFFICIENCY;
 		}
 	}
 
-- 
2.34.1

[PATCH v2 3/3] x86/topology: Add TOPO_CPU_TYPE_LOW_POWER

[Vishal Badole]

AMD heterogeneous parts report a third core type via CPUID
Fn0x80000026 EBX[31:28] (Extended CPU Topology, Core Type):

  0 - Performance
  1 - Efficiency
  2 - Low Power

get_topology_cpu_type() only translates the first two, so on parts
that ship low-power cores the third type falls through to
TOPO_CPU_TYPE_UNKNOWN. That has two visible effects:

  - /sys/kernel/debug/x86/topo/cpus/* reports cpu_type "unknown" via
    get_topology_cpu_type_name().

  - amd_get_boost_ratio_numerator() hits the default arm of its
    x86_topology_cpu_type switch and uses the
    CPPC_HIGHEST_PERF_PREFCORE fallback instead of scaling by
    amd_get_highest_perf() as efficiency cores do.

Add TOPO_CPU_TYPE_LOW_POWER, translate AMD_CPU_TYPE_LOW_POWER to it
in get_topology_cpu_type(), and expose a "low_power" name via
get_topology_cpu_type_name().

In amd_get_boost_ratio_numerator(), share the efficiency-core arm of
the switch with the new type so low-power cores scale by
amd_get_highest_perf() rather than the performance-core ceiling. The
new case sits under the existing
cpu_feature_enabled(X86_FEATURE_AMD_HTR_CORES) gate and therefore
applies to every HTR_CORES-capable AMD/Hygon part that reports core
type 2.

Signed-off-by: Vishal Badole <Vishal.Badole@amd.com>
---
 arch/x86/include/asm/processor.h      | 1 +
 arch/x86/kernel/acpi/cppc.c           | 3 ++-
 arch/x86/kernel/cpu/topology_common.c | 3 +++
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index fc0350fe8f5e..9e8183441888 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -73,6 +73,7 @@ enum x86_topology_cpu_type {
 	TOPO_CPU_TYPE_ANY = 0,
 	TOPO_CPU_TYPE_PERFORMANCE,
 	TOPO_CPU_TYPE_EFFICIENCY,
+	TOPO_CPU_TYPE_LOW_POWER,
 	TOPO_CPU_TYPE_UNKNOWN,
 };
 
diff --git a/arch/x86/kernel/acpi/cppc.c b/arch/x86/kernel/acpi/cppc.c
index b8f5dd0a8117..bbade0da5130 100644
--- a/arch/x86/kernel/acpi/cppc.c
+++ b/arch/x86/kernel/acpi/cppc.c
@@ -281,8 +281,9 @@ int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator)
 			/* use the max scale for performance cores */
 			*numerator = CPPC_HIGHEST_PERF_PERFORMANCE;
 			return 0;
+		case TOPO_CPU_TYPE_LOW_POWER:
 		case TOPO_CPU_TYPE_EFFICIENCY:
-			/* use the highest perf value for efficiency cores */
+			/* use the highest perf value for efficiency and low-power cores */
 			ret = amd_get_highest_perf(cpu, &tmp);
 			if (ret)
 				return ret;
diff --git a/arch/x86/kernel/cpu/topology_common.c b/arch/x86/kernel/cpu/topology_common.c
index 71b6c33afe0b..581f2fcd7e42 100644
--- a/arch/x86/kernel/cpu/topology_common.c
+++ b/arch/x86/kernel/cpu/topology_common.c
@@ -44,6 +44,7 @@ enum x86_topology_cpu_type get_topology_cpu_type(struct cpuinfo_x86 *c)
 		switch (c->topo.amd_type) {
 		case AMD_CPU_TYPE_PERFORMANCE:	return TOPO_CPU_TYPE_PERFORMANCE;
 		case AMD_CPU_TYPE_EFFICIENCY:	return TOPO_CPU_TYPE_EFFICIENCY;
+		case AMD_CPU_TYPE_LOW_POWER:	return TOPO_CPU_TYPE_LOW_POWER;
 		}
 	}
 
@@ -57,6 +58,8 @@ const char *get_topology_cpu_type_name(struct cpuinfo_x86 *c)
 		return "performance";
 	case TOPO_CPU_TYPE_EFFICIENCY:
 		return "efficiency";
+	case TOPO_CPU_TYPE_LOW_POWER:
+		return "low_power";
 	default:
 		return "unknown";
 	}
-- 
2.34.1