arm64: mm: Introduce PTE_WRITE
authorSteve Capper <Steve.Capper@arm.com>
Wed, 15 Jan 2014 14:07:13 +0000 (14:07 +0000)
committerCatalin Marinas <catalin.marinas@arm.com>
Fri, 31 Jan 2014 11:30:49 +0000 (11:30 +0000)
commitc2c93e5b7f3f42277ec25ff3746096abc0c0d0f7
treeef50b27ee3249facbc8dd809937445cdaefbc028
parent44b6dfc556811c0e6981329e29e1865fc7a8847d
arm64: mm: Introduce PTE_WRITE

We have the following means for encoding writable or dirty ptes:

                                PTE_DIRTY       PTE_RDONLY
!pte_dirty && !pte_write        0               1
!pte_dirty && pte_write         0               1
pte_dirty && !pte_write         1               1
pte_dirty && pte_write          1               0

So we can't distinguish between writable clean ptes and read only
ptes. This can cause problems with ptes being incorrectly flagged as
read only when they are writable but not dirty.

This patch introduces a new software bit PTE_WRITE which allows us to
correctly identify writable ptes. PTE_RDONLY is now only clear for
valid ptes where a page is both writable and dirty.

Signed-off-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
arch/arm64/include/asm/pgtable.h