linux-kernel - Re: [PATCH 4/5] context_tracking: Only define schedule_user() on !HAVE_CONTEXT_TRACKING

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 11 Nov 2020 15:34:58 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Phil Auld <pauld@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH 4/5] context_tracking: Only define schedule_user() on
 !HAVE_CONTEXT_TRACKING_OFFSTACK archs

On Tue, Oct 27, 2020 at 04:08:26PM +0100, Frederic Weisbecker wrote:
> schedule_user() was traditionally used by the entry code's tail to
> preempt userspace after the call to user_enter(). Indeed the call to
> user_enter() used to be performed upon syscall exit slow path which was
> right before the last opportunity to schedule() while resuming to
> userspace. The context tracking state had to be saved on the task stack
> and set back to CONTEXT_KERNEL temporarily in order to safely switch to
> another task.
> 
> Only a few archs use it now and those implementing
> HAVE_CONTEXT_TRACKING_OFFSTACK definetly can't rely on it.

powerpc64 and sparc64 only, right?

> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> Cc: Marcelo Tosatti <mtosatti@...hat.com>
> Cc: Paul E. McKenney <paulmck@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Phil Auld <pauld@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> ---
>  kernel/sched/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index c23d7cb5aee3..44426e5acde2 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4631,7 +4631,7 @@ void __sched schedule_idle(void)
>  	} while (need_resched());
>  }
>  
> -#ifdef CONFIG_CONTEXT_TRACKING
> +#if defined(CONFIG_CONTEXT_TRACKING) && !defined(CONFIG_HAVE_CONTEXT_TRACKING_OFFSTACK)
>  asmlinkage __visible void __sched schedule_user(void)
>  {
>  	/*
> -- 
> 2.25.1
>