From: Will Deacon <will.deacon@arm.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: dvlasenk@redhat.com, jpoimboe@redhat.com,
Julien Thierry <julien.thierry@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
catalin.marinas@arm.com, valentin.schneider@arm.com,
linux-kernel@vger.kernel.org,
Andy Lutomirski <luto@amacapital.net>,
mingo@redhat.com, james.morse@arm.com, luto@kernel.org,
brgerst@gmail.com, bp@alien8.de, tglx@linutronix.de,
torvalds@linux-foundation.org, Ingo Molnar <mingo@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch
Date: Thu, 21 Feb 2019 12:46:29 +0000 [thread overview]
Message-ID: <20190221124629.GA12696@fuggles.cambridge.arm.com> (raw)
In-Reply-To: <f8e99706-4e3b-68ec-7a3e-6e6dd876ad2f@zytor.com>
On Wed, Feb 20, 2019 at 02:55:59PM -0800, H. Peter Anvin wrote:
> On 2/19/19 4:48 AM, Will Deacon wrote:
> >
> > I think you'll still hate this, but could we not disable preemption during
> > the uaccess-enabled region, re-enabling it on the fault path after we've
> > toggled uaccess off and disable it again when we return back to the
> > uaccess-enabled region? Doesn't help with tracing, but it should at least
> > handle the common case.
> >
>
> There is a worse problem with this, I still realize: this would mean blocking
> preemption across what could possibly be a *very* large copy_from_user(), for
> example.
I don't think it's legitimate to call copy_{to,from}_user() inside a
user_access_{begin,end} region. You'd need to add some unsafe variants,
which could periodically disable uaccess and call cond_resched() inside
the loop to avoid the problem you're eluding to.
For existing callers of copy_{to,from}_user(), there's no issue as they
don't call into the scheduler during the copy operation. Exceptions are
handled fine by the code in mainline today.
GCC plugins are a cool idea, but I'm just a bit nervous about relying on
them for things like this.
Will
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WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will.deacon@arm.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@amacapital.net>,
Julien Thierry <julien.thierry@arm.com>,
Ingo Molnar <mingo@kernel.org>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, mingo@redhat.com,
catalin.marinas@arm.com, james.morse@arm.com,
valentin.schneider@arm.com, brgerst@gmail.com,
jpoimboe@redhat.com, luto@kernel.org, bp@alien8.de,
dvlasenk@redhat.com, torvalds@linux-foundation.org,
tglx@linutronix.de
Subject: Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch
Date: Thu, 21 Feb 2019 12:46:29 +0000 [thread overview]
Message-ID: <20190221124629.GA12696@fuggles.cambridge.arm.com> (raw)
In-Reply-To: <f8e99706-4e3b-68ec-7a3e-6e6dd876ad2f@zytor.com>
On Wed, Feb 20, 2019 at 02:55:59PM -0800, H. Peter Anvin wrote:
> On 2/19/19 4:48 AM, Will Deacon wrote:
> >
> > I think you'll still hate this, but could we not disable preemption during
> > the uaccess-enabled region, re-enabling it on the fault path after we've
> > toggled uaccess off and disable it again when we return back to the
> > uaccess-enabled region? Doesn't help with tracing, but it should at least
> > handle the common case.
> >
>
> There is a worse problem with this, I still realize: this would mean blocking
> preemption across what could possibly be a *very* large copy_from_user(), for
> example.
I don't think it's legitimate to call copy_{to,from}_user() inside a
user_access_{begin,end} region. You'd need to add some unsafe variants,
which could periodically disable uaccess and call cond_resched() inside
the loop to avoid the problem you're eluding to.
For existing callers of copy_{to,from}_user(), there's no issue as they
don't call into the scheduler during the copy operation. Exceptions are
handled fine by the code in mainline today.
GCC plugins are a cool idea, but I'm just a bit nervous about relying on
them for things like this.
Will
next prev parent reply other threads:[~2019-02-21 12:46 UTC|newest]
Thread overview: 171+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-15 13:58 [PATCH v3 0/4] uaccess: Add unsafe accessors for arm64 Julien Thierry
2019-01-15 13:58 ` Julien Thierry
2019-01-15 13:58 ` [PATCH v3 1/4] arm64: uaccess: Cleanup get/put_user() Julien Thierry
2019-01-15 13:58 ` Julien Thierry
2019-01-15 13:58 ` [PATCH v3 2/4] arm64: uaccess: Implement unsafe accessors Julien Thierry
2019-01-15 13:58 ` Julien Thierry
2019-01-15 13:58 ` [PATCH v3 3/4] uaccess: Check no rescheduling function is called in unsafe region Julien Thierry
2019-01-15 13:58 ` Julien Thierry
2019-01-30 16:58 ` Valentin Schneider
2019-01-30 16:58 ` Valentin Schneider
2019-02-04 13:27 ` Julien Thierry
2019-02-04 13:27 ` Julien Thierry
2019-02-11 13:45 ` Ingo Molnar
2019-02-11 13:45 ` Ingo Molnar
2019-02-11 13:51 ` Peter Zijlstra
2019-02-11 13:51 ` Peter Zijlstra
2019-02-12 9:15 ` Julien Thierry
2019-02-12 9:15 ` Julien Thierry
2019-02-13 8:21 ` Ingo Molnar
2019-02-13 8:21 ` Ingo Molnar
2019-02-13 10:35 ` Peter Zijlstra
2019-02-13 10:35 ` Peter Zijlstra
2019-02-13 10:50 ` Julien Thierry
2019-02-13 10:50 ` Julien Thierry
2019-02-13 13:17 ` Peter Zijlstra
2019-02-13 13:17 ` Peter Zijlstra
2019-02-13 13:20 ` Peter Zijlstra
2019-02-13 13:20 ` Peter Zijlstra
2019-02-13 14:00 ` Will Deacon
2019-02-13 14:00 ` Will Deacon
2019-02-13 14:07 ` Julien Thierry
2019-02-13 14:07 ` Julien Thierry
2019-02-13 14:17 ` Peter Zijlstra
2019-02-13 14:17 ` Peter Zijlstra
2019-02-13 14:24 ` Julien Thierry
2019-02-13 14:24 ` Julien Thierry
2019-02-13 14:40 ` Peter Zijlstra
2019-02-13 14:40 ` Peter Zijlstra
2019-02-13 15:08 ` Peter Zijlstra
2019-02-13 15:08 ` Peter Zijlstra
2019-02-13 14:25 ` Peter Zijlstra
2019-02-13 14:25 ` Peter Zijlstra
2019-02-13 14:39 ` Julien Thierry
2019-02-13 14:39 ` Julien Thierry
2019-02-13 14:41 ` Peter Zijlstra
2019-02-13 14:41 ` Peter Zijlstra
2019-02-13 15:45 ` Peter Zijlstra
2019-02-13 15:45 ` Peter Zijlstra
2019-02-13 18:54 ` Peter Zijlstra
2019-02-13 18:54 ` Peter Zijlstra
[not found] ` <D61C430D-4321-4114-AB85-671A3C7B8EAE@amacapital.net>
2019-02-13 22:21 ` Peter Zijlstra
2019-02-13 22:21 ` Peter Zijlstra
2019-02-13 22:49 ` Andy Lutomirski
2019-02-13 22:49 ` Andy Lutomirski
2019-02-14 10:14 ` [PATCH] sched/x86: Save [ER]FLAGS on context switch Peter Zijlstra
2019-02-14 10:14 ` Peter Zijlstra
2019-02-14 16:18 ` Brian Gerst
2019-02-14 16:18 ` Brian Gerst
2019-02-14 19:34 ` Peter Zijlstra
2019-02-14 19:34 ` Peter Zijlstra
2019-02-15 14:34 ` Brian Gerst
2019-02-15 14:34 ` Brian Gerst
2019-02-15 17:18 ` Linus Torvalds
2019-02-15 17:18 ` Linus Torvalds
2019-02-15 17:40 ` Peter Zijlstra
2019-02-15 17:40 ` Peter Zijlstra
2019-02-15 18:28 ` Andy Lutomirski
2019-02-15 18:28 ` Andy Lutomirski
2019-02-15 23:34 ` Peter Zijlstra
2019-02-15 23:34 ` Peter Zijlstra
2019-02-16 0:21 ` Linus Torvalds
2019-02-16 0:21 ` Linus Torvalds
2019-02-16 10:32 ` Peter Zijlstra
2019-02-16 10:32 ` Peter Zijlstra
2019-02-16 4:06 ` hpa
2019-02-16 4:06 ` hpa
2019-02-16 10:30 ` Peter Zijlstra
2019-02-16 10:30 ` Peter Zijlstra
2019-02-18 22:30 ` H. Peter Anvin
2019-02-18 22:30 ` H. Peter Anvin
2019-02-19 0:24 ` Linus Torvalds
2019-02-19 0:24 ` Linus Torvalds
2019-02-19 2:20 ` Andy Lutomirski
2019-02-19 2:20 ` Andy Lutomirski
2019-02-19 2:46 ` H. Peter Anvin
2019-02-19 2:46 ` H. Peter Anvin
2019-02-19 9:07 ` Julien Thierry
2019-02-19 9:07 ` Julien Thierry
2019-02-19 8:53 ` Julien Thierry
2019-02-19 8:53 ` Julien Thierry
2019-02-19 9:15 ` Peter Zijlstra
2019-02-19 9:15 ` Peter Zijlstra
2019-02-19 9:19 ` Peter Zijlstra
2019-02-19 9:19 ` Peter Zijlstra
2019-02-19 9:04 ` Peter Zijlstra
2019-02-19 9:04 ` Peter Zijlstra
2019-02-19 9:21 ` hpa
2019-02-19 9:21 ` hpa
2019-02-19 9:44 ` Peter Zijlstra
2019-02-19 9:44 ` Peter Zijlstra
2019-02-19 11:38 ` Thomas Gleixner
2019-02-19 11:38 ` Thomas Gleixner
2019-02-19 11:58 ` Peter Zijlstra
2019-02-19 11:58 ` Peter Zijlstra
2019-02-19 12:48 ` Will Deacon
2019-02-19 12:48 ` Will Deacon
2019-02-20 22:55 ` H. Peter Anvin
2019-02-20 22:55 ` H. Peter Anvin
2019-02-21 12:06 ` Julien Thierry
2019-02-21 12:06 ` Julien Thierry
2019-02-21 21:35 ` Thomas Gleixner
2019-02-21 21:35 ` Thomas Gleixner
2019-02-21 22:08 ` Linus Torvalds
2019-02-21 22:08 ` Linus Torvalds
2019-02-22 12:58 ` Peter Zijlstra
2019-02-22 12:58 ` Peter Zijlstra
2019-02-22 18:10 ` Thomas Gleixner
2019-02-22 18:10 ` Thomas Gleixner
2019-02-22 22:26 ` [RFC][PATCH] objtool: STAC/CLAC validation Peter Zijlstra
2019-02-22 22:26 ` Peter Zijlstra
2019-02-22 23:34 ` Linus Torvalds
2019-02-22 23:34 ` Linus Torvalds
2019-02-23 8:43 ` Peter Zijlstra
2019-02-23 8:43 ` Peter Zijlstra
2019-02-22 23:39 ` hpa
2019-02-22 23:39 ` hpa
2019-02-23 8:39 ` Peter Zijlstra
2019-02-23 8:39 ` Peter Zijlstra
2019-02-25 8:47 ` hpa
2019-02-25 8:47 ` hpa
2019-02-25 13:21 ` Peter Zijlstra
2019-02-25 13:21 ` Peter Zijlstra
2019-03-01 15:07 ` Peter Zijlstra
2019-03-01 15:07 ` Peter Zijlstra
2019-02-25 8:49 ` hpa
2019-02-25 8:49 ` hpa
2019-02-22 23:55 ` Andy Lutomirski
2019-02-22 23:55 ` Andy Lutomirski
2019-02-23 8:37 ` Peter Zijlstra
2019-02-23 8:37 ` Peter Zijlstra
2019-02-23 10:52 ` Peter Zijlstra
2019-02-23 10:52 ` Peter Zijlstra
2019-02-25 10:51 ` Peter Zijlstra
2019-02-25 10:51 ` Peter Zijlstra
2019-02-25 11:53 ` Peter Zijlstra
2019-02-25 11:53 ` Peter Zijlstra
2019-02-25 15:36 ` Andy Lutomirski
2019-02-25 15:36 ` Andy Lutomirski
2019-02-23 0:34 ` Andy Lutomirski
2019-02-23 1:12 ` Linus Torvalds
2019-02-23 1:16 ` Andy Lutomirski
2019-02-23 1:33 ` Linus Torvalds
2019-02-23 1:40 ` Linus Torvalds
2019-02-25 8:33 ` Julien Thierry
2019-02-25 8:33 ` Julien Thierry
2019-02-25 11:55 ` Peter Zijlstra
2019-02-25 11:55 ` Peter Zijlstra
2019-02-21 12:46 ` Will Deacon [this message]
2019-02-21 12:46 ` [PATCH] sched/x86: Save [ER]FLAGS on context switch Will Deacon
2019-02-21 22:06 ` Andy Lutomirski
2019-02-21 22:06 ` Andy Lutomirski
2019-02-18 9:03 ` [PATCH v2] " Peter Zijlstra
2019-02-18 9:03 ` Peter Zijlstra
2019-02-13 23:19 ` [PATCH v3 3/4] uaccess: Check no rescheduling function is called in unsafe region Linus Torvalds
2019-02-13 23:19 ` Linus Torvalds
2019-01-15 13:58 ` [PATCH v3 4/4] arm64: uaccess: Implement user_access_region_active Julien Thierry
2019-01-15 13:58 ` Julien Thierry
2019-01-25 14:27 ` [PATCH v3 0/4] uaccess: Add unsafe accessors for arm64 Catalin Marinas
2019-01-25 14:27 ` Catalin Marinas
2019-01-30 16:17 ` Julien Thierry
2019-01-30 16:17 ` Julien Thierry
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