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Subject: Re: [RFC PATCH 04/10 v2 ] x86/fpu: eager switch PKRU state
From:   Rik van Riel <riel@surriel.com>
To:     Paolo Bonzini <pbonzini@redhat.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        Radim =?UTF-8?Q?Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>,
        kvm@vger.kernel.org, "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Tue, 18 Sep 2018 11:11:20 -0400
In-Reply-To: <7e9a13f3-93f5-fe4a-20d2-f4f9407bd43b@redhat.com>
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         <8e5b64e4-b3e6-f884-beb6-b7b69ab2d8c1@redhat.com>
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         <20180918142701.atfb4ul45k7tl6ew@linutronix.de>
         <7e9a13f3-93f5-fe4a-20d2-f4f9407bd43b@redhat.com>
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On Tue, 2018-09-18 at 17:07 +0200, Paolo Bonzini wrote:
> On 18/09/2018 16:27, Sebastian Andrzej Siewior wrote:
> > > Likewise, move this to fpu__clear and outside "if
> > > (static_cpu_has(X86_FEATURE_FPU))"?
> >=20
> > okay. But if there is no FPU we did not save/restore the pkru
> > value. Is
> > this supposed to be an improvement?
>=20
> Honestly it just seemed "more correct", but now that I think about
> it,
> kernel threads should run with PKRU=3D0.  maybe there's a preexisting
> bug
> that your patch has the occasion to fix.

I don't think it matters what the PKRU state is
for kernel threads, since kernel PTEs should not
be using protection keys anyway.

--=20
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