linux-kernel - Re: [PATCH] x86: do not overrun page table ranges in gup

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Date:	Tue, 29 Jul 2008 04:51:05 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Johannes Weiner <hannes@...urebad.de>, akpm@...uxfoundation.org,
	torvalds@...uxfoundation.org, npiggin@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: do not overrun page table ranges in gup

On Mon, Jul 28, 2008 at 05:39:18PM -0700, Linus Torvalds wrote:
> 
> 
> On Mon, 28 Jul 2008, Linus Torvalds wrote:
> > 
> > So no, the right fix would be to align 'start' first, which means that 
> > everything else (including 'end') will be page-aligned. Aligning just one 
> > or the other is very very wrong.
> 
> Does this work?
> 
> Not pretty, but it stands _some_ chance of being correct.

vmsplice01 doesn't crash now.

> --- a/arch/x86/mm/gup.c
> +++ b/arch/x86/mm/gup.c
> @@ -223,14 +223,17 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
>  			struct page **pages)
>  {
>  	struct mm_struct *mm = current->mm;
> -	unsigned long end = start + (nr_pages << PAGE_SHIFT);
> -	unsigned long addr = start;
> +	unsigned long addr, len, end;
>  	unsigned long next;
>  	pgd_t *pgdp;
>  	int nr = 0;
>  
> +	start &= PAGE_MASK;
> +	addr = start;
> +	len = (unsigned long) nr_pages << PAGE_SHIFT;
> +	end = start + len;
>  	if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
> -					start, nr_pages*PAGE_SIZE)))
> +					start, len)))
>  		goto slow_irqon;
>  
>  	/*

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