linux-kernel - Re: [PATCH 3.4 47/88] mm: add kmap_to

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Date:	Tue, 10 Jun 2014 16:04:53 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Hugh Dickins <hughd@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ben Hutchings <ben@...adent.org.uk>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH 3.4 47/88] mm: add kmap_to_page()

>> +struct page *kmap_to_page(void *vaddr)
>> +{
>> +	unsigned long addr = (unsigned long)vaddr;
>> +
>> +	if (addr >= PKMAP_ADDR(0) && addr <= PKMAP_ADDR(LAST_PKMAP)) {
>> +		int i = (addr - PKMAP_ADDR(0)) >> PAGE_SHIFT;
>> +		return pte_page(pkmap_page_table[i]);
>> +	}
>> +
>> +	return virt_to_page(addr);
>> +}
>> +
>>  static void flush_all_zero_pkmaps(void)
>>  {
>>  	int i;
> 
> I think this needs the following on top:
> 
> commit 498c2280212327858e521e9d21345d4cc2637f54
> Author: Will Deacon <will.deacon@....com>
> Date:   Fri Nov 16 14:15:00 2012 -0800
> 

Thanks Hugh. Hi Greg, please pick up this fix patch, Thanks a lot!

Yijing.


>     mm: highmem: don't treat PKMAP_ADDR(LAST_PKMAP) as a highmem address
>     
>     kmap_to_page returns the corresponding struct page for a virtual address
>     of an arbitrary mapping.  This works by checking whether the address
>     falls in the pkmap region and using the pkmap page tables instead of the
>     linear mapping if appropriate.
>     
>     Unfortunately, the bounds checking means that PKMAP_ADDR(LAST_PKMAP) is
>     incorrectly treated as a highmem address and we can end up walking off
>     the end of pkmap_page_table and subsequently passing junk to pte_page.
>     
>     This patch fixes the bound check to stay within the pkmap tables.
>     
>     Signed-off-by: Will Deacon <will.deacon@....com>
>     Cc: Mel Gorman <mgorman@...e.de>
>     Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>     Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> 
> diff --git a/mm/highmem.c b/mm/highmem.c
> index d517cd16a6eb..2da13a5c50e2 100644
> --- a/mm/highmem.c
> +++ b/mm/highmem.c
> @@ -98,7 +98,7 @@ struct page *kmap_to_page(void *vaddr)
>  {
>  	unsigned long addr = (unsigned long)vaddr;
>  
> -	if (addr >= PKMAP_ADDR(0) && addr <= PKMAP_ADDR(LAST_PKMAP)) {
> +	if (addr >= PKMAP_ADDR(0) && addr < PKMAP_ADDR(LAST_PKMAP)) {
>  		int i = (addr - PKMAP_ADDR(0)) >> PAGE_SHIFT;
>  		return pte_page(pkmap_page_table[i]);
>  	}
> 
> 
> .
> 


-- 
Thanks!
Yijing

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