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

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Message-ID: <20160805135308.GT6879@twins.programming.kicks-ass.net>
Date:	Fri, 5 Aug 2016 15:53:08 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org, x86@...nel.org,
	Borislav Petkov <bp@...e.de>,
	Andy Lutomirski <luto@...nel.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH] x86/mm: disable preemption during CR3 read+write

On Fri, Aug 05, 2016 at 03:37:39PM +0200, Sebastian Andrzej Siewior wrote:
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> index 4e5be94e079a..1ee065954e24 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ 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();
>  }

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>