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Commit 73a1441a authored by Aneesh Kumar K.V's avatar Aneesh Kumar K.V Committed by Michael Ellerman
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powerpc/mm/subpage: Clear RWX bit to indicate no access 



Subpage protection used to depend on the _PAGE_USER bit to implement no
access mode. This patch switches that to use _PAGE_RWX. We clear Read,
Write and Execute access from the pte instead of clearing _PAGE_USER
now. This was done so that we can switch to _PAGE_PRIVILEGED in a 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 simpler to clear RWX acecss to indicate no access.

We still don't insert hash ptes for no access implied by !_PAGE_RWX.
Hence we should not get PROT_FAULT with change.

Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent c7d54842

arch/powerpc/mm/hash_utils_64.c

+8 −3
Original line number Diff line number Diff line
@@ -921,7 +921,7 @@ 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)

{
@@ -947,8 +947,13 @@ 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;

}