linux-kernel - Re: [PATCH] x86/arch_prctl/64: restore accidentally removed put_cpu in ARCH_SET

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Message-ID: <CALCETrUe_6+p0FJnTn=QVM8NutUibFEWfE_CmUFro8bqWJ+G6g@mail.gmail.com>
Date:	Thu, 12 May 2016 08:11:49 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	X86 ML <x86@...nel.org>, Borislav Petkov <bp@...en8.de>
Cc:	Andy Lutomirski <luto@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Mateusz Guzik <mguzik@...hat.com>
Subject: Re: [PATCH] x86/arch_prctl/64: restore accidentally removed put_cpu
 in ARCH_SET_GS

On Tue, May 10, 2016 at 1:56 PM, Mateusz Guzik <mguzik@...hat.com> wrote:
> This fixes 731e33e39a5b95ad770 "Remove FSBASE/GSBASE < 4G optimization"
>
> Signed-off-by: Mateusz Guzik <mguzik@...hat.com>
> ---
>  arch/x86/kernel/process_64.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> index 4285f6a..6b16c36 100644
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -541,6 +541,7 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
>                         load_gs_index(0);
>                         ret = wrmsrl_safe(MSR_KERNEL_GS_BASE, addr);
>                 }
> +               put_cpu();
>                 break;
>         case ARCH_SET_FS:
>                 /* Not strictly needed for fs, but do it for symmetry
> --
> 1.8.3.1
>

Ingo, can you apply this before the merge window opens?

I just noticed that you weren't cc'd, so I'll repeat my ack:

Acked-by: Andy Lutomirski <luto@...nel.org>

And I'll ask, since IIRC you wrote it: would it make sense to augment
lockdep_sys_exit to see if preemption got left disabled?

Thanks,
Andy