[PATCH PATCH 1/9] x86/cpu/topology: Add x86_cpu_type to struct cpuinfo_topology

Pawan Gupta
2024-06-17T09:11:28Z

Sometimes it is required to identify the type of a core for taking specific
actions e.g. intel_pstate driver uses the core type to determine CPU
scaling. Also, some CPU vulnerabilities only affect a specific CPU type
e.g. RFDS only affects Intel Atom. For hybrid systems that have variants
P+E, P-only(Core) and E-only(Atom), it gets challenging to identify which
variant is vulnerable to a specific vulnerability, as these variants share
the same family, model and stepping.

Such processors do have CPUID fields that uniquely identify them. Like,
P+E, P-only and E-only enumerates CPUID.1A.CORE_TYPE, while P+E
additionally enumerates CPUID.7.HYBRID. Linux does not currently use this
field.

Add a new field cpu_type to struct cpuinfo_topology which can be used to
match a CPU based on its type.

The cpu_type is populated in the below debugfs file:

# cat /sys/kernel/debug/x86/topo/cpus/N

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
---
arch/x86/include/asm/processor.h | 3 +++
arch/x86/include/asm/topology.h | 9 +++++++++
arch/x86/kernel/cpu/debugfs.c | 1 +
arch/x86/kernel/cpu/topology_common.c | 9 +++++++++
4 files changed, 22 insertions(+)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index cb4f6c513c48..f310a7fb4e00 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -95,6 +95,9 @@ struct cpuinfo_topology {
// Core ID relative to the package
u32 core_id;

+ // CPU-type e.g. performance, efficiency etc.
+ u8 cpu_type;
+
// Logical ID mappings
u32 logical_pkg_id;
u32 logical_die_id;
diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
index abe3a8f22cbd..b28ad9422afb 100644
--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -41,6 +41,14 @@
/* Mappings between logical cpu number and node number */
DECLARE_EARLY_PER_CPU(int, x86_cpu_to_node_map);

+#define X86_CPU_TYPE_INTEL_SHIFT 24
+
+enum x86_topo_cpu_type {
+ X86_CPU_TYPE_UNKNOWN = 0,
+ X86_CPU_TYPE_INTEL_ATOM = 0x20,
+ X86_CPU_TYPE_INTEL_CORE = 0x40,
+};
+
#ifdef CONFIG_DEBUG_PER_CPU_MAPS
/*
* override generic percpu implementation of cpu_to_node
@@ -139,6 +147,7 @@ extern const struct cpumask *cpu_clustergroup_mask(int cpu);
#define topology_logical_die_id(cpu) (cpu_data(cpu).topo.logical_die_id)
#define topology_die_id(cpu) (cpu_data(cpu).topo.die_id)
#define topology_core_id(cpu) (cpu_data(cpu).topo.core_id)
+#define topology_cpu_type(cpu) (cpu_data(cpu).topo.cpu_type)
#define topology_ppin(cpu) (cpu_data(cpu).ppin)

#define topology_amd_node_id(cpu) (cpu_data(cpu).topo.amd_node_id)
diff --git a/arch/x86/kernel/cpu/debugfs.c b/arch/x86/kernel/cpu/debugfs.c
index 3baf3e435834..b1c9bafe6c39 100644
--- a/arch/x86/kernel/cpu/debugfs.c
+++ b/arch/x86/kernel/cpu/debugfs.c
@@ -22,6 +22,7 @@ static int cpu_debug_show(struct seq_file *m, void *p)
seq_printf(m, "die_id: %u\n", c->topo.die_id);
seq_printf(m, "cu_id: %u\n", c->topo.cu_id);
seq_printf(m, "core_id: %u\n", c->topo.core_id);
+ seq_printf(m, "cpu_type: %x\n", c->topo.cpu_type);
seq_printf(m, "logical_pkg_id: %u\n", c->topo.logical_pkg_id);
seq_printf(m, "logical_die_id: %u\n", c->topo.logical_die_id);
seq_printf(m, "llc_id: %u\n", c->topo.llc_id);
diff --git a/arch/x86/kernel/cpu/topology_common.c b/arch/x86/kernel/cpu/topology_common.c
index 9a6069e7133c..be82c8769bb2 100644
--- a/arch/x86/kernel/cpu/topology_common.c
+++ b/arch/x86/kernel/cpu/topology_common.c
@@ -140,6 +140,14 @@ static void parse_topology(struct topo_scan *tscan, bool early)
}
}

+static void topo_set_cpu_type(struct cpuinfo_x86 *c)
+{
+ c->topo.cpu_type = X86_CPU_TYPE_UNKNOWN;
+
+ if (c->x86_vendor == X86_VENDOR_INTEL && cpuid_eax(0) >= 0x1a)
+ c->topo.cpu_type = cpuid_eax(0x1a) >> X86_CPU_TYPE_INTEL_SHIFT;
+}
+
static void topo_set_ids(struct topo_scan *tscan, bool early)
{
struct cpuinfo_x86 *c = tscan->c;
@@ -190,6 +198,7 @@ void cpu_parse_topology(struct cpuinfo_x86 *c)
}

topo_set_ids(&tscan, false);
+ topo_set_cpu_type(c);
}

void __init cpu_init_topology(struct cpuinfo_x86 *c)

--
2.34.1