Subpage protection used to depend on _PAGE_USER bit to implement no
access mode. This patch switch that to use _PAGE_RWX. We clear READ,
Write and Execute access from pte instead of clearing _PAGE_USER now.
This was done so that we can switch to _PAGE_PRIVILEGED in later patch.
subpage_protection() returns pte bits that need to be cleared.
Instead of updating the interface to handle no-access in a separate way,
it appears simple to clear RWX acecss to indicate no access.
We still don't insert hash pte for no access implied by !_PAGE_RWX.
Hence we should not get PROT_FAULT with change.
Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
---
arch/powerpc/mm/hash_utils_64.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index ea23403b3fc0..ec37f4b0a8ff 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -917,7 +917,7 @@ void demote_segment_4k(struct mm_struct *mm, unsigned long
addr)
* Userspace sets the subpage permissions using the subpage_prot system call.
*
* Result is 0: full permissions, _PAGE_RW: read-only,
- * _PAGE_USER or _PAGE_USER|_PAGE_RW: no access.
+ * _PAGE_RWX: no access.
*/
static int subpage_protection(struct mm_struct *mm, unsigned long ea)
{
@@ -943,8 +943,13 @@ static int subpage_protection(struct mm_struct *mm,
unsigned long ea)
/* extract 2-bit bitfield for this 4k subpage */
spp >>= 30 - 2 * ((ea >> 12) & 0xf);
- /* turn 0,1,2,3 into combination of _PAGE_USER and _PAGE_RW */
- spp = ((spp & 2) ? _PAGE_USER : 0) | ((spp & 1) ? _PAGE_RW : 0);
+ /*
+ * 0 -> full premission
+ * 1 -> Read only
+ * 2 -> no access.
+ * We return the flag that need to be cleared.
+ */
+ spp = ((spp & 2) ? _PAGE_RWX : 0) | ((spp & 1) ? _PAGE_WRITE : 0);
return spp;
}
--
2.5.0
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