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

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Message-ID: <3d869bdf-5ca7-d2ea-cc85-eb461b37b207@intel.com>
Date:   Wed, 26 Feb 2020 15:40:30 -0800
From:   Jacob Keller <jacob.e.keller@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        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>
Subject: Re: [PATCH] x86/pkeys: Manually set X86_FEATURE_OSPKE to preserve
 existing changes



On 2/26/2020 3:32 PM, Dave Hansen wrote:
> 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.
> 


I tripped over it. It's possible someone else has as well, but I haven't
heard from anyone else.

Thanks,
Jake