linux-kernel - RE: [PATCH v5 03/10] platform/x86/intel/ifs: Add stub driver for In-Field Scan

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Date:   Wed, 4 May 2022 16:24:50 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        "hdegoede@...hat.com" <hdegoede@...hat.com>,
        "markgross@...nel.org" <markgross@...nel.org>
CC:     "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "corbet@....net" <corbet@....net>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "Joseph, Jithu" <jithu.joseph@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
Subject: RE: [PATCH v5 03/10] platform/x86/intel/ifs: Add stub driver for
 In-Field Scan

>> +static const struct x86_cpu_id ifs_cpu_ids[] __initconst = {
>> +	X86_MATCH(SAPPHIRERAPIDS_X),
>
> Why do we need a model match here? The core capabilities MSR is only
> available when X86_FEATURE_CORE_CAPABILITIES is set:
>
>    "If CPUID.(EAX=07H, ECX=0):EDX[30] = 1.
>     This MSR provides an architectural enumeration
>     function for model-specific behavior."
>
> So checking for Intel Fam6 ANYMODEL and X86_FEATURE_CORE_CAPABILITIES is
> sufficient, no?

IA32_CORE_CAPABILITES is a nightmare. Although it is an architectural
register, the bits inside it are model specific.

In particular bit 2 (which we check here for the existence of the INTEGRITY
MSR) has been assigned for other use on other models. See SDM volume 4
table 2-45 where bit 2 means FUSA supported on 06_8C and 06_8D (Tigerlake
mobile and desktop). Ditto in table 2-46 (Alderlake and Raptorlake).

> We really don't need more match id tables with gazillions of CPU models.

Sadly we do :-(

-Tony