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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Radim Krcmar <rkrcmar@redhat.com>, kvm list <kvm@vger.kernel.org>,
	"Jason A. Donenfeld" <Jason@zx2c4.com>,
	Rik van Riel <riel@surriel.com>
Subject: Re: [PATCH 05/11] x86/fpu: set PKRU state for kernel threads
Date: Thu, 18 Oct 2018 18:26:44 +0200	[thread overview]
Message-ID: <20181018162644.qqjkzoqn2fleyi2b@linutronix.de> (raw)
In-Reply-To: <CALCETrUdxsFA5g0M9uRFktfdi=mxK_g3kBfs-VxwDZ0xWqjFAQ@mail.gmail.com>

On 2018-10-12 11:02:18 [-0700], Andy Lutomirski wrote:
> On Fri, Oct 12, 2018 at 10:54 AM Dave Hansen
> <dave.hansen@linux.intel.com> wrote:
> >
> > On 10/04/2018 07:05 AM, Sebastian Andrzej Siewior wrote:
> > > The PKRU value is not set for kernel threads because they do not have
> > > the ->initialized value set. As a result the kernel thread has a random
> > > PKRU value set which it inherits from the previous task.
> > > It has been suggested by Paolo Bonzini to set it for kernel threads, too
> > > because it might be a fix.
> > > I *think* this is not required because the kernel threads don't copy
> > > data to/from userland and don't have access to any userspace mm in
> > > general.
> > > However there is this use_mm(). If we gain a mm by use_mm() we don't
> > > have a matching PKRU value because those are per thread. It has been
> > > suggested to use 0 as the PKRU value but this would bypass PKRU.
> > >
> > > Set the initial (default) PKRU value for kernel threads.
> >
> > We might want to do this for cleanliness reasons...  Maybe.
> >
> > But this *should* have no practical effects.  Kernel threads have no
> > real 'mm' and no user pages.  They should not have do access to user
> > mappings.  Protection keys *only* apply to user mappings.  Thus,
> > logically, they should never be affected by PKRU values.
> >
> > So I'm kinda missing the point of the patch.
> 
> use_mm().

So. I would drop that patch from queue. Anyone feels different about it?

Sebastian

  reply	other threads:[~2018-10-18 16:26 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-04 14:05 [PATCH 00/11 v3] x86: load FPU registers on return to userland Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 01/11] x86/entry: remove _TIF_ALLWORK_MASK Sebastian Andrzej Siewior
2018-10-11 16:27   ` Borislav Petkov
2018-10-04 14:05 ` [PATCH 02/11] x86/fpu: add (__)make_fpregs_active helpers Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 03/11] x86/fpu: make __raw_xsave_addr() use feature number instead of mask Sebastian Andrzej Siewior
2018-10-11 17:30   ` Christophe de Dinechin
2018-10-18 11:19     ` Sebastian Andrzej Siewior
2018-10-12 15:52   ` Dave Hansen
2018-10-18 11:17     ` Sebastian Andrzej Siewior
2018-10-18 11:21       ` Sebastian Andrzej Siewior
2018-10-17 10:01   ` Borislav Petkov
2018-10-18 11:48     ` Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 04/11] x86/fpu: eager switch PKRU state Sebastian Andrzej Siewior
2018-10-12 17:51   ` Dave Hansen
2018-10-12 18:09     ` Andy Lutomirski
2018-10-12 19:44       ` Dave Hansen
2018-10-18 16:13     ` Sebastian Andrzej Siewior
2018-10-18 17:50       ` Dave Hansen
2018-10-04 14:05 ` [PATCH 05/11] x86/fpu: set PKRU state for kernel threads Sebastian Andrzej Siewior
2018-10-12 17:54   ` Dave Hansen
2018-10-12 18:02     ` Andy Lutomirski
2018-10-18 16:26       ` Sebastian Andrzej Siewior [this message]
2018-10-18 16:48         ` Andy Lutomirski
2018-10-18 17:47           ` Dave Hansen
2018-10-18 18:25           ` Sebastian Andrzej Siewior
2018-10-18 20:46             ` Andy Lutomirski
2018-10-18 20:56               ` Dave Hansen
2018-10-18 21:24                 ` Sebastian Andrzej Siewior
2018-10-18 21:58                   ` Andy Lutomirski
2018-10-19  7:44               ` Paolo Bonzini
2018-10-19 16:59                 ` Andy Lutomirski
2018-10-19 17:01                   ` Dave Hansen
2018-10-19 17:37                     ` Andy Lutomirski
2018-10-19 18:26                       ` Dave Hansen
2018-10-04 14:05 ` [PATCH 06/11] x86/pkeys: make init_pkru_value static Sebastian Andrzej Siewior
2018-10-12 17:55   ` Dave Hansen
2018-10-04 14:05 ` [PATCH 07/11] x86/pkeys: Drop the preempt-disable section Sebastian Andrzej Siewior
2018-10-12 17:58   ` Dave Hansen
2018-10-12 18:07     ` Andy Lutomirski
2018-10-12 20:26       ` Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 08/11] x86/fpu: Always store the registers in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2018-10-11 17:50   ` Christophe de Dinechin
2018-10-11 21:18     ` Andy Lutomirski
2018-10-12 18:15   ` Dave Hansen
2018-11-02 14:42     ` Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 09/11] x86/entry: add TIF_LOAD_FPU Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 10/11] x86/fpu: prepare copy_fpstate_to_sigframe for TIF_LOAD_FPU Sebastian Andrzej Siewior
2018-10-12 19:40   ` Dave Hansen
2018-10-15 15:24     ` Borislav Petkov
2018-11-02 15:44       ` Sebastian Andrzej Siewior
2018-11-02 22:55     ` Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 11/11] x86/fpu: defer FPU state load until return to userspace Sebastian Andrzej Siewior
2018-10-04 16:14   ` Andy Lutomirski
2018-10-12 20:25     ` Sebastian Andrzej Siewior
2018-10-04 16:45 ` [PATCH 00/11 v3] x86: load FPU registers on return to userland Rik van Riel
2018-10-04 16:50   ` Andy Lutomirski
2018-10-05 11:55   ` Sebastian Andrzej Siewior

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