[stable] ARM: 8108/1: mm: Introduce {pte,pmd}_isset and {pte,pmd}_isclear

[Ben Hutchings]

On Mon, 2014-12-15 at 14:25 +0000, Luis Henriques wrote:
> 3.16.7-ckt3 -stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Steven Capper <steve.capper@xxxxxxxxxx>
> 
> commit f2950706871c4b6e8c0f0d7c3f62d35930b8de63 upstream.
> 
> Long descriptors on ARM are 64 bits, and some pte functions such as
> pte_dirty return a bitwise-and of a flag with the pte value. If the
> flag to be tested resides in the upper 32 bits of the pte, then we run
> into the danger of the result being dropped if downcast.
> 
> For example:
> 	gather_stats(page, md, pte_dirty(*pte), 1);
> where pte_dirty(*pte) is downcast to an int.
> 
> This patch introduces a new macro pte_isset which performs the bitwise
> and, then performs a double logical invert (where needed) to ensure
> predictable downcasting. The logical inverse pte_isclear is also
> introduced.
> 
> Equivalent pmd functions for Transparent HugePages have also been
> added.
> 
> Signed-off-by: Steve Capper <steve.capper@xxxxxxxxxx>
> Reviewed-by: Will Deacon <will.deacon@xxxxxxx>
> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
> Cc: Hou Pengyang <houpengyang@xxxxxxxxxx>
> Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
[...]

This has only been applied to 3.16 so far, but it appears to be suitable
for every branch from 3.4 onwards as ARM LPAE was introduced in 3.3.

Ben.

-- 
Ben Hutchings
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