[PATCH PATCH v2 1/9] x86/cpu/topology: Add CPU type to struct cpuinfo_topology

[Pawan Gupta]

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 hw_cpu_type to struct cpuinfo_topology which can be used to
match a CPU based on its type.

The hw_cpu_type is populated in the below debugfs file:

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

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
---
 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..d8d715fcc25c 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -105,6 +105,9 @@ struct cpuinfo_topology {
 	// Cache level topology IDs
 	u32			llc_id;
 	u32			l2c_id;
+
+	// Hardware defined CPU-type
+	u8			hw_cpu_type;
 };
 
 struct cpuinfo_x86 {
diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
index abe3a8f22cbd..717fdb928dc3 100644
--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -33,6 +33,14 @@
 #include <linux/numa.h>
 #include <linux/cpumask.h>
 
+#define X86_CPU_TYPE_INTEL_SHIFT	24
+
+enum x86_hw_topo_cpu_type {
+	X86_HW_CPU_TYPE_UNKNOWN		= 0,
+	X86_HW_CPU_TYPE_INTEL_ATOM	= 0x20,
+	X86_HW_CPU_TYPE_INTEL_CORE	= 0x40,
+};
+
 #ifdef CONFIG_NUMA
 
 #include <asm/mpspec.h>
@@ -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_hw_cpu_type(cpu)		(cpu_data(cpu).topo.hw_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..8082e03a5976 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, "hw_cpu_type:         %x\n", c->topo.hw_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..8b47bd6b0623 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_hw_cpu_type(struct cpuinfo_x86 *c)
+{
+	c->topo.hw_cpu_type = X86_HW_CPU_TYPE_UNKNOWN;
+
+	if (c->x86_vendor == X86_VENDOR_INTEL && c->cpuid_level >= 0x1a)
+		c->topo.hw_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_hw_cpu_type(c);
 }
 
 void __init cpu_init_topology(struct cpuinfo_x86 *c)

-- 
2.34.1