linux-kernel - Re: [PATCH] x86/pkeys: Manually set X86_FEATURE

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Date:   Wed, 26 Feb 2020 15:32:21 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org
Cc:     "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jacob Keller <jacob.e.keller@...el.com>
Subject: Re: [PATCH] x86/pkeys: Manually set X86_FEATURE_OSPKE to preserve
 existing changes

On 2/26/20 3:16 PM, Sean Christopherson wrote:
> Explicitly set X86_FEATURE_OSPKE via set_cpu_cap() instead of calling
> get_cpu_cap() to pull the feature bit from CPUID after enabling CR4.PKE.

First of all,

Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>

I don't remember whether it was you or someone else inside Intel, but
someone was tripping over this recently.

I do think we need a bit more care in how we deal with dynamic CPUID
bits.  I think you'd agree that it's a bit haphazard.  For instance, I
went looking for where we set X86_FEATURE_OSXSAVE after the

        cr4_set_bits(X86_CR4_OSXSAVE);

inside fpu__init_cpu_xstate() makes it appear.  I couldn't find one, not
that we would notice since we suppress it from /proc/cpuinfo.