linux-kernel - Re: [PATCH PATCH 9/9] x86/rfds: Exclude P-only parts from the RFDS affected list

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Date: Mon, 17 Jun 2024 11:19:40 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Andrew Cooper <andrew.cooper3@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	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>
Subject: Re: [PATCH PATCH 9/9] x86/rfds: Exclude P-only parts from the RFDS
 affected list

On Mon, Jun 17, 2024 at 07:34:22AM -0700, Dave Hansen wrote:
> On 6/17/24 02:43, Andrew Cooper wrote:
> > On 17/06/2024 10:12 am, Pawan Gupta wrote:
> >> +	VULNBL_INTEL_CPU_TYPE (RAPTORLAKE,	X86_CPU_TYPE_INTEL_ATOM,	RFDS),
> >> +	VULNBL_INTEL_CPU_TYPE (ALDERLAKE,	X86_CPU_TYPE_INTEL_ATOM,	RFDS),
> > 
> > How does this work?
> > 
> > Being __initconst, this is only evaluated on the BSP.
> > 
> > P-only and mixed P/E systems won't see X86_CPU_TYPE_INTEL_ATOM, even if
> > there are ATOM APs to bring up later.
> 
> The X86_CPU_TYPE_* is only used on the boot CPU on non-hybrids.  Hybrids
> (independent of the boot CPU type) should be considered vulnerable no
> matter what.

Yes. This is done in x86_match_cpu_type(), that matches all cpu-types on hybrids:

  static bool x86_match_cpu_type(struct cpuinfo_x86 *c, const struct x86_cpu_id)
  {
     if (m->cpu_type == X86_CPU_TYPE_ANY)
         return true;

     /* Hybrid CPUs are special, they are assumed to match all cpu-types */
     if (boot_cpu_has(X86_FEATURE_HYBRID_CPU))
         return true;

     return c->topo.cpu_type == m->cpu_type;
  }