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From: Andy Lutomirski <luto@amacapital.net>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Sebastian Andrzej Siewior" <bigeasy@linutronix.de>,
	"Rik van Riel" <riel@surriel.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	"Andy Lutomirski" <luto@kernel.org>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	kvm@vger.kernel.org, "Jason A. Donenfeld" <Jason@zx2c4.com>
Subject: Re: [RFC PATCH 04/10 v2 ] x86/fpu: eager switch PKRU state
Date: Wed, 19 Sep 2018 12:49:35 -0700	[thread overview]
Message-ID: <27496B23-92A0-462C-A198-6A4413634488@amacapital.net> (raw)
In-Reply-To: <099b9f82-e162-c91a-bc51-aa1ac0cd50aa@redhat.com>



> On Sep 19, 2018, at 10:00 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
>> On 19/09/2018 18:57, Sebastian Andrzej Siewior wrote:
>>> On 2018-09-19 07:55:51 [+0200], Paolo Bonzini wrote:
>>> A kthread can do use_mm/unuse_mm.
>> 
>> indeed. The FPU struct for the kernel thread isn't valid / does not
>> contain the expected PKRU value. So loading the pkru value from the
>> struct FPU does not work as expected. We could set it to 0 for a kernel
>> thread so we don't end up with a random value.
>> If we want to get this usecase working then we would have to move pkru
>> value from FPU to mm_struct and consider it in use_mm(). Do we want
>> this?
> 
> As a start, I think keeping it in the FPU struct but loading it
> unconditionally will work.  kthreads will not obey PKU but it will be
> better already.
> 
> I honestly don't know if PKRU should be per-mm, I don't know mm very
> well despite my brilliant observation above. :)
> 
> 

It must be per thread.  I don’t think it’s possible to have sane semantics per mm.

I also think that use_mm should set PKRU to the same value that signal handlers use.  If we use 0, it’s a recipe for accidental PK bypass.

  parent reply	other threads:[~2018-09-19 19:49 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-12 13:33 [RFC PATCH] x86: load FPU registers on return to userland Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 01/10] x86/entry: remove _TIF_ALLWORK_MASK Sebastian Andrzej Siewior
2018-09-27 14:21   ` Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 02/10] kvm: x86: make kvm_{load|put}_guest_fpu() static Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 03/10] x86/fpu: add (__)make_fpregs_active helpers Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 04/10] x86/fpu: eager switch PKRU state Sebastian Andrzej Siewior
2018-09-12 14:18   ` Paolo Bonzini
2018-09-12 15:24     ` Andy Lutomirski
2018-09-12 15:30       ` Paolo Bonzini
2018-09-14 20:35     ` [RFC PATCH 04/10 v2 ] " Sebastian Andrzej Siewior
2018-09-17  8:37       ` Paolo Bonzini
2018-09-18 14:27         ` Sebastian Andrzej Siewior
2018-09-18 15:07           ` Paolo Bonzini
2018-09-18 15:11             ` Rik van Riel
2018-09-18 15:29               ` Paolo Bonzini
2018-09-18 16:04                 ` Sebastian Andrzej Siewior
2018-09-18 17:29                   ` Rik van Riel
2018-09-19  5:55                     ` Paolo Bonzini
2018-09-19 16:57                       ` Sebastian Andrzej Siewior
2018-09-19 17:00                         ` Paolo Bonzini
2018-09-19 17:19                           ` Sebastian Andrzej Siewior
2018-09-19 19:38                           ` Rik van Riel
2018-09-19 19:49                           ` Andy Lutomirski [this message]
2018-09-12 15:20   ` [RFC PATCH 04/10] " Andy Lutomirski
2018-09-12 15:30     ` Rik van Riel
2018-09-12 15:49       ` Andy Lutomirski
2018-09-19 16:58         ` Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 05/10] x86/pkeys: Drop the preempt-disable section Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 06/10] x86/fpu: Always store the registers in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 07/10] x86/entry: add TIF_LOAD_FPU Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 08/10] x86/fpu: prepare copy_fpstate_to_sigframe for TIF_LOAD_FPU Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 09/10] x86/fpu: copy non-resident FPU state at fork time Sebastian Andrzej Siewior
2018-09-12 13:33 ` [RFC PATCH 10/10] x86/fpu: defer FPU state load until return to userspace Sebastian Andrzej Siewior
2018-09-12 15:47   ` Andy Lutomirski
2018-09-19 17:05     ` Sebastian Andrzej Siewior
2018-09-21  3:45       ` Andy Lutomirski
2018-09-21  4:15         ` Andy Lutomirski
2018-09-26 11:12           ` Sebastian Andrzej Siewior
2018-09-26 14:34             ` Andy Lutomirski
2018-09-26 15:32               ` Sebastian Andrzej Siewior
2018-09-26 16:24                 ` Andy Lutomirski

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