linux-kernel - Re: [PATCH] x86/mm: disable preemption during CR3 read+write

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Date:	Fri, 05 Aug 2016 10:38:33 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:	x86@...nel.org, Borislav Petkov <bp@...e.de>,
	Andy Lutomirski <luto@...nel.org>,
	Mel Gorman <mgorman@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86/mm: disable preemption during CR3 read+write

On Fri, 2016-08-05 at 15:37 +0200, Sebastian Andrzej Siewior wrote:
> 
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -135,7 +135,14 @@ static inline void
> cr4_set_bits_and_update_boot(unsigned long mask)
>  
>  static inline void __native_flush_tlb(void)
>  {
> +	/*
> +	 * if current->mm == NULL then we borrow a mm which may
> change during a
> +	 * task switch and therefore we must not be preempted while
> we write CR3
> +	 * back.
> +	 */
> +	preempt_disable();
>  	native_write_cr3(native_read_cr3());
> +	preempt_enable();
>  }

That is one subtle race!

Acked-by: Rik van Riel <riel@...hat.com>

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