Re: [PATCH] x86/topo: Map vendor CPU types to generic Linux such types

[Pawan Gupta]

On Mon, Jul 20, 2026 at 08:18:58PM -0700, Borislav Petkov wrote:
> On Wed, Jul 08, 2026 at 01:24:05AM +0200, Thomas Gleixner wrote:
> > If that's the only case to handle, then sure that open coded check is
> > fine.
> 
> This is ontop of tip:x86/cpu which already has Pawan's change that drops the
> one Intel-specific CPU type use.
> 
> It boots here so... :-P
> 
> ---
> From: "Borislav Petkov (AMD)" <bp@xxxxxxxxx>
> Date: Thu, 2 Jul 2026 17:00:28 -0700
> Subject: [PATCH] x86/topo: Map vendor CPU types to generic Linux such types
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
> 
> 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@xxxxxxxxx>
> Link: https://lore.kernel.org/r/20260629094349.533301-2-Vishal.Badole@xxxxxxx
> ---
>  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,

I don't really understand the purpose of TOPO_CPU_TYPE_ANY here. In the cpu
matching infrastructure, X86_CPU_TYPE_ANY makes sense. Here I fail to
understand how is TOPO_CPU_TYPE_ANY different from UNKNOWN? A table passed
to x86_match_cpu() with X86_CPU_TYPE_ANY entry will match any CPU type
including TOPO_CPU_TYPE_UNKNOWN.

> +	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,
> -};
...
>  /**
>   * 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)

In line with what Thomas pointed that cpu_type is not a system property, I
suggest matching cpu_type should be dropped from x86_match_cpu(). More so
because it only uses boot_cpu_data and misses the other types of secondary
CPUs. I feel it is not a reliable way to match CPU types. Thoughts?

>  			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)) {

Slightly unrelated to this patch, on AMD is it that hw_cpu_type only
available on hybrid systems? On Intel ...

> +		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);

... hw_cpu_type could be enumerated on non-hybrid parts.

> +		}
> +
>  		break;
>  	}
>  }