linux-kernel - Re: [PATCH v2 1/9] x86/cpu/topology: Add CPU type to struct cpuinfo

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Date: Fri, 28 Jun 2024 10:32:09 -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 v2 1/9] x86/cpu/topology: Add CPU type to struct
 cpuinfo_topology

On Fri, Jun 28, 2024 at 10:03:05AM +0200, Borislav Petkov wrote:
> On Thu, Jun 27, 2024 at 01:44:06PM -0700, Pawan Gupta wrote:
> > The hw_cpu_type is populated in the below debugfs file:
> > 
> >   # cat /sys/kernel/debug/x86/topo/cpus/#
> 
> What "below debugfs file"? A '#'?

That is the number of the CPU. If it is causing confusion, I can will
change it to N, or say # means the number of the CPU.

> > 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);
> 
> Yeah, no, we're not going to perpetuate this silliness of printing hex
> values without a preceding "0x".

I thought about that, but the other fields are also printed without a
preceding "0x":

          seq_printf(m, "initial_apicid:      %x\n", c->topo.initial_apicid);
          seq_printf(m, "apicid:              %x\n", c->topo.apicid);
	  ...

I will change those too, probably in a separate patch.

> > +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;
> > +}
> 
> Why isn't this happening in cpu/intel.c? And then you don't need yet
> another silly function.

I was preferring to keep the topology related code in one place. Would it
make sense to keep it in Intel specific leg in parse_topology() as below:

---
diff --git a/arch/x86/kernel/cpu/topology_common.c b/arch/x86/kernel/cpu/topology_common.c
index 8b47bd6b0623..c8869e75365f 100644
--- a/arch/x86/kernel/cpu/topology_common.c
+++ b/arch/x86/kernel/cpu/topology_common.c
@@ -87,6 +87,7 @@ static void parse_topology(struct topo_scan *tscan, bool early)
 		.cu_id			= 0xff,
 		.llc_id			= BAD_APICID,
 		.l2c_id			= BAD_APICID,
+		.hw_cpu_type		= X86_HW_CPU_TYPE_UNKNOWN,
 	};
 	struct cpuinfo_x86 *c = tscan->c;
 	struct {
@@ -132,6 +133,8 @@ 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) >> X86_CPU_TYPE_INTEL_SHIFT;
 		break;
 	case X86_VENDOR_HYGON:
 		if (IS_ENABLED(CONFIG_CPU_SUP_HYGON))