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Message-ID: <CAMzpN2g54zWYOAzmJdUm+1ziivkciLEeSDp4+b89KHkO4Lem+A@mail.gmail.com>
Date: Fri, 15 Feb 2019 09:34:33 -0500
From: Brian Gerst <brgerst@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...capital.net>,
Julien Thierry <julien.thierry@....com>,
Will Deacon <will.deacon@....com>,
Ingo Molnar <mingo@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-arm-kernel@...ts.infradead.org,
Ingo Molnar <mingo@...hat.com>,
Catalin Marinas <catalin.marinas@....com>,
James Morse <james.morse@....com>,
"H. Peter Anvin" <hpa@...or.com>, valentin.schneider@....com,
Josh Poimboeuf <jpoimboe@...hat.com>,
Andy Lutomirski <luto@...nel.org>,
Borislav Petkov <bp@...en8.de>,
Denys Vlasenko <dvlasenk@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch
On Thu, Feb 14, 2019 at 2:34 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, Feb 14, 2019 at 11:18:01AM -0500, Brian Gerst wrote:
>
> > > --- a/arch/x86/include/asm/switch_to.h
> > > +++ b/arch/x86/include/asm/switch_to.h
> > > @@ -40,6 +40,7 @@ asmlinkage void ret_from_fork(void);
> > > * order of the fields must match the code in __switch_to_asm().
> > > */
> > > struct inactive_task_frame {
> > > + unsigned long flags;
> > > #ifdef CONFIG_X86_64
> > > unsigned long r15;
> > > unsigned long r14;
> >
> > flags should be initialized in copy_thread_tls(). I think the new
> > stack is zeroed already, but it would be better to explicitly set it.
>
> Ah indeed. I somehow misread that code and thought we got initialized
> with a copy of current.
>
> Something like the below, right?
>
> ---
>
> --- a/arch/x86/kernel/process_32.c
> +++ b/arch/x86/kernel/process_32.c
> @@ -127,6 +127,7 @@ int copy_thread_tls(unsigned long clone_
> struct task_struct *tsk;
> int err;
>
> + frame->flags = 0;
> frame->bp = 0;
> frame->ret_addr = (unsigned long) ret_from_fork;
> p->thread.sp = (unsigned long) fork_frame;
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -392,6 +392,7 @@ int copy_thread_tls(unsigned long clone_
> childregs = task_pt_regs(p);
> fork_frame = container_of(childregs, struct fork_frame, regs);
> frame = &fork_frame->frame;
> + frame->flags = 0;
> frame->bp = 0;
> frame->ret_addr = (unsigned long) ret_from_fork;
> p->thread.sp = (unsigned long) fork_frame;
Yes, this looks good.
--
Brian Gerst
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