linux-kernel - Re: [PATCH v4 02/10] x86/cpu/topology: Add CPU type to struct cpuinfo

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Message-ID: <20241021163656.zyyugk4vyqyhzh3i@desk>
Date: Mon, 21 Oct 2024 09:36:56 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	daniel.sneddon@...ux.intel.com, tony.luck@...el.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Brice Goglin <brice.goglin@...il.com>,
	Mario Limonciello <mario.limonciello@....com>,
	Perry Yuan <Perry.Yuan@....com>,
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: Re: [PATCH v4 02/10] x86/cpu/topology: Add CPU type to struct
 cpuinfo_topology

On Mon, Oct 21, 2024 at 03:38:06PM +0200, Borislav Petkov wrote:
> On October 18, 2024 10:30:53 PM GMT+02:00, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com> wrote:
> >I will drop "core", but can we keep "native"? "native" is used in SDM to
> >define this field. Also model_id could be confused with model number.
> >
> >  From Intel SDM Vol. 2A:
> >
> >  Bits 23-00: Native model ID of the core. The core-type and native model
> >  ID can be used to uniquely identify the microarchitecture of the core.
> >  This native model ID is not unique across core types, and not related to
> >  the model ID reported in CPUID leaf 01H, and does not identify the SOC.
> 
> I'm still not clear on what "native" is supposed to mean here?
>
> The core is born this way and then it changes... so this is its native
> model ID? Weird...

In a hybrid system the model number reported by CPUID could represent
multiple core-types. As model number is same for all cores, it is
insufficient to uniquely identify the microarchitecture of a core. I
believe "native model ID" bridges that gap as it is specific to a core.

> >Yes, topo.hw_cpu_type is initialized to TOPO_HW_CPU_TYPE_UNKNOWN. We should
> >not ideally need the vendor check at all. As long as topo.hw_cpu_type has
> >the core type, returning it should be enough here. For Intel hw_cpu_type
> >also has the native_model_id, that is why we need the vendor check.
> >
> >If AMD or other vendors have similar use case, it makes sense to add the
> >explicit vendor check. Please let me know if thats the likely case.
> 
> Yes, it either needs to be vendor-agnostic or you need to accommodate all
> vendors. Former sounds cleaner...

Ok, I will add an explicit vendor check for AMD as well.