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

Mario Limonciello
2024-06-18T21:33:12Z

On 6/17/2024 04:11, Pawan Gupta wrote:
> 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,
> +};
> +

There is another patch series [1] in flight right now that is trying to
get CPU types for AMD hetero designs as well.

I think the way you're doing it is a bit better though.

What do you think about having a common enum rather with words that are
marketing strings? We could have a monotonically increasing enum then
too instead of a random bit mask.

Something like:

enum x86_topo_cpu_type {
X86_CPU_TYPE_UNKNOWN = 0,
X86_CPU_TYPE_PERFORMANCE = 1,
X86_CPU_TYPE_EFFICIENCY = 2,
};

Then as additional core types are added for any vendor those can be
added here with a description of what they are.

The logic for topo_set_cpu_type() below can map out any bit mask and
shift from a lookup path into this standard enum then.

If you do it this way we can lump the AMD hetero look up stuff into
topo_set_cpu_type() as another case.

[1]
https://lore.kernel.org/linux-pm/cover.1718606975.git.perry.yuan@amd.com/T/#mc65457f33331bba0d7d4fef1907d2fef14fc3fd8

> #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)
>