[PATCH 2/2] powerpc/mm/subpage: Fix subpage protection with 4K hpte config

[Aneesh Kumar K.V]

With Linux page size of 64K and hardware only supporting 4K hpte, if
we use subpage protection, we always fail for the subpage 0 as shown
below (using the selftest subpage_prot test).

520175565: (4520111850): Failed at 0x0x3fffad4b0000 (p=13,sp=0,w=0), want=fault, got=pass !
4520890210: (4520826495): Failed at 0x0x3fffad5b0000 (p=29,sp=0,w=0), want=fault, got=pass !
4521574251: (4521510536): Failed at 0x0x3fffad6b0000 (p=45,sp=0,w=0), want=fault, got=pass !
4522258324: (4522194609): Failed at 0x0x3fffad7b0000 (p=61,sp=0,w=0), want=fault, got=pass !

This is because hash preload wrongly insert the hpte entry for subpage 0
without looking at the subapge protection information. Don't do hash
page table entry preload if we have subpage protection configured for
that range.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
---
 arch/powerpc/mm/hash_utils_64.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 262082e51db1..b5a454415215 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -1329,15 +1329,26 @@ void hash_preload(struct mm_struct *mm, unsigned long ea,
 	unsigned long vsid;
 	pgd_t *pgdir;
 	pte_t *ptep;
+	int psize;
 	unsigned long flags;
 	int rc, ssize, update_flags = 0;
 
 	BUG_ON(REGION_ID(ea) != USER_REGION_ID);
 
 #ifdef CONFIG_PPC_MM_SLICES
-	/* We only prefault standard pages for now */
-	if (unlikely(get_slice_psize(mm, ea) != mm->context.user_psize))
+	psize = get_slice_psize(mm, ea);
+	/*
+	 * We only prefault standard pages
+	 */
+	if (psize != mm->context.user_psize)
 		return;
+#ifdef CONFIG_PPC_64K_PAGES
+	/*
+	 * Don't prefault is subpage protection is enabled for that ea
+	 */
+	if ((psize == MMU_PAGE_4K) && subpage_protection(mm, ea))
+		return;
+#endif
 #endif
 
 	DBG_LOW("hash_preload(mm=%p, mm->pgdir=%p, ea=%016lx, access=%lx,"
-- 
2.7.4