Sometimes it is required to take actions based on if a CPU is a performance
or efficiency core. As an example, intel_pstate driver uses the Intel
core-type to determine CPU scaling. Also, some CPU vulnerabilities only
affect a specific CPU type, like RFDS only affects Intel Atom. Hybrid
systems that have variants P+E, P-only(Core) and E-only(Atom), it is not
straightforward to identify which variant is affected by a type specific
vulnerability.

Such processors do have CPUID field that can uniquely identify them. Like,
P+E, P-only and E-only enumerates CPUID.1A.CORE_TYPE identification, while
P+E additionally enumerates CPUID.7.HYBRID. Based on this information, it
is possible for boot CPU to identify if a system has mixed CPU types.

Add a new field hw_cpu_type to struct cpuinfo_topology that stores the
hardware specific CPU type. This saves the overhead of IPIs to get the CPU
type of a different CPU. CPU type is populated early in the boot process,
before vulnerabilities are enumerated.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
---
 arch/x86/include/asm/cpu.h            |  6 ++++++
 arch/x86/include/asm/processor.h      | 11 +++++++++++
 arch/x86/include/asm/topology.h       |  8 ++++++++
 arch/x86/kernel/cpu/debugfs.c         |  1 +
 arch/x86/kernel/cpu/intel.c           |  5 +++++
 arch/x86/kernel/cpu/topology_common.c | 11 +++++++++++
 6 files changed, 42 insertions(+)

diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index aa30fd8cad7f..f480c36a07b7 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -32,6 +32,7 @@ extern bool handle_user_split_lock(struct pt_regs *regs, long error_code);
 extern bool handle_guest_split_lock(unsigned long ip);
 extern void handle_bus_lock(struct pt_regs *regs);
 u8 get_this_hybrid_cpu_type(void);
+u32 intel_hw_native_model_id(struct cpuinfo_x86 *c);
 #else
 static inline void __init sld_setup(struct cpuinfo_x86 *c) {}
 static inline bool handle_user_split_lock(struct pt_regs *regs, long error_code)
@@ -50,6 +51,11 @@ static inline u8 get_this_hybrid_cpu_type(void)
 {
 	return 0;
 }
+
+static u32 intel_hw_native_model_id(struct cpuinfo_x86 *c)
+{
+	return 0;
+}
 #endif
 #ifdef CONFIG_IA32_FEAT_CTL
 void init_ia32_feat_ctl(struct cpuinfo_x86 *c);
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index a75a07f4931f..2f10d3f3158c 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -105,6 +105,17 @@ struct cpuinfo_topology {
 	// Cache level topology IDs
 	u32			llc_id;
 	u32			l2c_id;
+
+	// Hardware defined CPU-type
+	union {
+		u32		hw_cpu_type;
+		struct {
+			/* CPUID.1A.EAX[23-0] */
+			u32	intel_core_native_model_id:24;
+			/* CPUID.1A.EAX[31-24] */
+			u32	intel_core_type:8;
+		};
+	};
 };
 
 struct cpuinfo_x86 {
diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
index abe3a8f22cbd..93142eaea0b5 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 x86_topology_hw_cpu_type {
+	TOPO_HW_CPU_TYPE_UNKNOWN	= 0,
+	TOPO_HW_CPU_TYPE_INTEL_ATOM	= 0x20,
+	TOPO_HW_CPU_TYPE_INTEL_CORE	= 0x40,
+};
+
 struct x86_topology_system {
 	unsigned int	dom_shifts[TOPO_MAX_DOMAIN];
 	unsigned int	dom_size[TOPO_MAX_DOMAIN];
@@ -149,6 +155,8 @@ extern unsigned int __max_threads_per_core;
 extern unsigned int __num_threads_per_package;
 extern unsigned int __num_cores_per_package;
 
+enum x86_topology_hw_cpu_type topology_hw_cpu_type(struct cpuinfo_x86 *c);
+
 static inline unsigned int topology_max_packages(void)
 {
 	return __max_logical_packages;
diff --git a/arch/x86/kernel/cpu/debugfs.c b/arch/x86/kernel/cpu/debugfs.c
index ca373b990c47..d1731e0e36b0 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:       0x%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/intel.c b/arch/x86/kernel/cpu/intel.c
index 08b95a35b5cb..e47a53280369 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -1297,3 +1297,8 @@ u8 get_this_hybrid_cpu_type(void)
 
 	return cpuid_eax(0x0000001a) >> X86_HYBRID_CPU_TYPE_ID_SHIFT;
 }
+
+u32 intel_hw_native_model_id(struct cpuinfo_x86 *c)
+{
+	return c->topo.intel_core_native_model_id;
+}
diff --git a/arch/x86/kernel/cpu/topology_common.c b/arch/x86/kernel/cpu/topology_common.c
index 9a6069e7133c..e4814cd3d8ae 100644
--- a/arch/x86/kernel/cpu/topology_common.c
+++ b/arch/x86/kernel/cpu/topology_common.c
@@ -27,6 +27,14 @@ void topology_set_dom(struct topo_scan *tscan, enum x86_topology_domains dom,
 	}
 }
 
+enum x86_topology_hw_cpu_type topology_hw_cpu_type(struct cpuinfo_x86 *c)
+{
+	if (c->x86_vendor == X86_VENDOR_INTEL)
+		return c->topo.intel_core_type;
+
+	return c->topo.hw_cpu_type;
+}
+
 static unsigned int __maybe_unused parse_num_cores_legacy(struct cpuinfo_x86 *c)
 {
 	struct {
@@ -87,6 +95,7 @@ static void parse_topology(struct topo_scan *tscan, bool early)
 		.cu_id			= 0xff,
 		.llc_id			= BAD_APICID,
 		.l2c_id			= BAD_APICID,
+		.hw_cpu_type		= TOPO_HW_CPU_TYPE_UNKNOWN,
 	};
 	struct cpuinfo_x86 *c = tscan->c;
 	struct {
@@ -132,6 +141,8 @@ 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.hw_cpu_type = cpuid_eax(0x1a);
 		break;
 	case X86_VENDOR_HYGON:
 		if (IS_ENABLED(CONFIG_CPU_SUP_HYGON))

-- 
2.34.1

Hi Pawan,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 7c626ce4bae1ac14f60076d00eafe71af30450ba]

url:    https://github.com/intel-lab-lkp/linux/commits/Pawan-Gupta/x86-cpu-Prepend-0x-to-the-hex-values-in-cpu_debug_show/20240816-122157
base:   7c626ce4bae1ac14f60076d00eafe71af30450ba
patch link:    https://lore.kernel.org/r/20240815-add-cpu-type-v3-2-234162352057%40linux.intel.com
patch subject: [PATCH v3 02/10] x86/cpu/topology: Add CPU type to struct cpuinfo_topology
config: x86_64-randconfig-013-20240816 (https://download.01.org/0day-ci/archive/20240817/202408170359.M7BAB0O0-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240817/202408170359.M7BAB0O0-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202408170359.M7BAB0O0-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from arch/x86/power/cpu.c:25:
>> arch/x86/include/asm/cpu.h:55:12: warning: 'intel_hw_native_model_id' defined but not used [-Wunused-function]
      55 | static u32 intel_hw_native_model_id(struct cpuinfo_x86 *c)
         |            ^~~~~~~~~~~~~~~~~~~~~~~~


vim +/intel_hw_native_model_id +55 arch/x86/include/asm/cpu.h

    54	
  > 55	static u32 intel_hw_native_model_id(struct cpuinfo_x86 *c)
    56	{
    57		return 0;
    58	}
    59	#endif
    60	#ifdef CONFIG_IA32_FEAT_CTL
    61	void init_ia32_feat_ctl(struct cpuinfo_x86 *c);
    62	#else
    63	static inline void init_ia32_feat_ctl(struct cpuinfo_x86 *c) {}
    64	#endif
    65	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki