From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Brian Gerst <brgerst@gmail.com>,
Andy Lutomirski <luto@amacapital.net>,
Julien Thierry <julien.thierry@arm.com>,
Will Deacon <will.deacon@arm.com>, Ingo Molnar <mingo@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"linux-alpha@vger.kernel.org"
<linux-arm-kernel@lists.infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Catalin Marinas <catalin.marinas@arm.com>,
James Morse <james.morse@arm.com>,
"H. Peter Anvin" <hpa@zytor.com>,
valentin.schneider@arm.com, Josh Poimboeuf <jpoimboe@redhat.com>,
Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
Denys Vlasenko <dvlasenk@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch
Date: Sat, 16 Feb 2019 00:34:14 +0100 [thread overview]
Message-ID: <20190215233414.GS32534@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190215174034.GP32494@hirez.programming.kicks-ass.net>
On Fri, Feb 15, 2019 at 06:40:34PM +0100, Peter Zijlstra wrote:
> On Fri, Feb 15, 2019 at 09:18:00AM -0800, Linus Torvalds wrote:
> > On Thu, Feb 14, 2019 at 11:34 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > Something like the below, right?
> > >
> > > + frame->flags = 0;
> > > + frame->flags = 0;
> >
> > Those are not valid flag values.
> >
> > Can you popf them? Yes.
> >
> > Do they make sense? No.
> >
> > It has the IF flag clear, for example. Is that intentional? If it is,
>
> Uhmm. yeah, that's bonkers. We should have interrupts disabled here.
> I'll go read up on the eflags and figure out what they _should_ be right
> about there.
I misread (I'm forever confused about what way around IF goes), but you
said it right; IF=0 is interrupts disabled and we very much have that in
the middle of context switch.
(just for giggles I set IF for the initial flags value; and it comes
unstuck _real_ quick)
Now, EFLAGS bit 1 is supposedly always 1, but it really doesn't seem to
matter for POPF.
I went through the other flags, and aside from VIP/VIF (I've no clue),
they looks like 0 should be just fine.
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Julien Thierry <julien.thierry@arm.com>,
Brian Gerst <brgerst@gmail.com>, "H. Peter Anvin" <hpa@zytor.com>,
Will Deacon <will.deacon@arm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
valentin.schneider@arm.com, Ingo Molnar <mingo@redhat.com>,
James Morse <james.morse@arm.com>,
Andy Lutomirski <luto@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Borislav Petkov <bp@alien8.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
"linux-alpha@vger.kernel.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch
Date: Sat, 16 Feb 2019 00:34:14 +0100 [thread overview]
Message-ID: <20190215233414.GS32534@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190215174034.GP32494@hirez.programming.kicks-ass.net>
On Fri, Feb 15, 2019 at 06:40:34PM +0100, Peter Zijlstra wrote:
> On Fri, Feb 15, 2019 at 09:18:00AM -0800, Linus Torvalds wrote:
> > On Thu, Feb 14, 2019 at 11:34 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > Something like the below, right?
> > >
> > > + frame->flags = 0;
> > > + frame->flags = 0;
> >
> > Those are not valid flag values.
> >
> > Can you popf them? Yes.
> >
> > Do they make sense? No.
> >
> > It has the IF flag clear, for example. Is that intentional? If it is,
>
> Uhmm. yeah, that's bonkers. We should have interrupts disabled here.
> I'll go read up on the eflags and figure out what they _should_ be right
> about there.
I misread (I'm forever confused about what way around IF goes), but you
said it right; IF=0 is interrupts disabled and we very much have that in
the middle of context switch.
(just for giggles I set IF for the initial flags value; and it comes
unstuck _real_ quick)
Now, EFLAGS bit 1 is supposedly always 1, but it really doesn't seem to
matter for POPF.
I went through the other flags, and aside from VIP/VIF (I've no clue),
they looks like 0 should be just fine.
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next prev parent reply other threads:[~2019-02-15 23:34 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 [this message]
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 ` [PATCH] sched/x86: Save [ER]FLAGS on context switch Will Deacon
2019-02-21 12:46 ` 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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