linux-kernel - Re: [PATCH v6 04/25] x86/fpu/xstate: Introduce kernel dynamic xfeature set

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Message-ID: <17c85a216c87a2a91bdfd8f34659df1dfb1d8f63.camel@redhat.com>
Date:   Tue, 31 Oct 2023 19:44:20 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     "Yang, Weijiang" <weijiang.yang@...el.com>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "peterz@...radead.org" <peterz@...radead.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "john.allen@....com" <john.allen@....com>
Subject: Re: [PATCH v6 04/25] x86/fpu/xstate: Introduce kernel dynamic
 xfeature set

On Fri, 2023-09-15 at 14:42 +0800, Yang, Weijiang wrote:
> On 9/15/2023 8:24 AM, Edgecombe, Rick P wrote:
> > On Thu, 2023-09-14 at 02:33 -0400, Yang Weijiang wrote:
> > > +static void __init init_kernel_dynamic_xfeatures(void)
> > > +{
> > > +       unsigned short cid;
> > > +       int i;
> > > +
> > > +       for (i = 0; i < ARRAY_SIZE(xsave_kernel_dynamic_xfeatures);
> > > i++) {
> > > +               cid = xsave_kernel_dynamic_xfeatures[i];
> > > +
> > > +               if (cid && boot_cpu_has(cid))
> > > +                       fpu_kernel_dynamic_xfeatures |= BIT_ULL(i);
> > > +       }
> > > +}
> > > +
> > I think this can be part of the max_features calculation that uses
> > xsave_cpuid_features when you use use a fixed mask like Dave suggested
> > in the other patch.
> 
> Yes, the max_features has already included CET supervisor state bit. After  use
> fixed mask, this function is not needed.
> 
> 
My 0.2 cents are also on having XFEATURE_MASK_KERNEL_DYNAMIC macro instead.

Best regards,
	Maxim Levitsky