Re: [PATCH 3.4 47/88] mm: add kmap_to_page()

Yijing Wang
2014-06-10T08:05:37Z

>> +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@arm.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@arm.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-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