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Subject: Re: [RFC PATCH 04/10 v2 ] x86/fpu: eager switch PKRU state
To:     Rik van Riel <riel@surriel.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        kvm@vger.kernel.org, "Jason A. Donenfeld" <Jason@zx2c4.com>
References: <20180912133353.20595-1-bigeasy@linutronix.de>
 <20180912133353.20595-5-bigeasy@linutronix.de>
 <8e5b64e4-b3e6-f884-beb6-b7b69ab2d8c1@redhat.com>
 <20180914203501.qibhpmueosvkr74w@linutronix.de>
 <a239e97a-d1a1-388e-5db9-10758c33d702@redhat.com>
 <20180918142701.atfb4ul45k7tl6ew@linutronix.de>
 <7e9a13f3-93f5-fe4a-20d2-f4f9407bd43b@redhat.com>
 <83e271e1298d603c1105dd0dbea32d67da9cf1fa.camel@surriel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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Message-ID: <36e8493f-f994-e885-8fe6-2f0d4a9904a1@redhat.com>
Date:   Tue, 18 Sep 2018 17:29:52 +0200
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From: Paolo Bonzini <pbonzini@redhat.com>
To: Rik van Riel <riel@surriel.com>,
 Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
 Andy Lutomirski <luto@kernel.org>, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?=
 <rkrcmar@redhat.com>, kvm@vger.kernel.org,
 "Jason A. Donenfeld" <Jason@zx2c4.com>
Message-ID: <36e8493f-f994-e885-8fe6-2f0d4a9904a1@redhat.com>
Subject: Re: [RFC PATCH 04/10 v2 ] x86/fpu: eager switch PKRU state
References: <20180912133353.20595-1-bigeasy@linutronix.de>
 <20180912133353.20595-5-bigeasy@linutronix.de>
 <8e5b64e4-b3e6-f884-beb6-b7b69ab2d8c1@redhat.com>
 <20180914203501.qibhpmueosvkr74w@linutronix.de>
 <a239e97a-d1a1-388e-5db9-10758c33d702@redhat.com>
 <20180918142701.atfb4ul45k7tl6ew@linutronix.de>
 <7e9a13f3-93f5-fe4a-20d2-f4f9407bd43b@redhat.com>
 <83e271e1298d603c1105dd0dbea32d67da9cf1fa.camel@surriel.com>
In-Reply-To: <83e271e1298d603c1105dd0dbea32d67da9cf1fa.camel@surriel.com>

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On 18/09/2018 17:11, Rik van Riel wrote:
> 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))"?
>>>
>>> okay. But if there is no FPU we did not save/restore the pkru
>>> value. Is
>>> this supposed to be an improvement?
>>
>> 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.
>=20
> I don't think it matters what the PKRU state is
> for kernel threads, since kernel PTEs should not
> be using protection keys anyway.

What about copy_from/to_user?

Paolo


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