powerpc/mm/hash64: Fix subpage protection with 4K HPTE config

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 0x3fffad4b0000 (p=13,sp=0,w=0), want=fault, got=pass !
  4520890210: (4520826495): Failed at 0x3fffad5b0000 (p=29,sp=0,w=0), want=fault, got=pass !
  4521574251: (4521510536): Failed at 0x3fffad6b0000 (p=45,sp=0,w=0), want=fault, got=pass !
  4522258324: (4522194609): Failed at 0x3fffad7b0000 (p=61,sp=0,w=0), want=fault, got=pass !

This is because hash preload wrongly inserts the HPTE entry for subpage
0 without looking at the subpage protection information.

Fix it by teaching should_hash_preload() not to preload if we have
subpage protection configured for that range.

It appears this has been broken since it was introduced in 2008.

Fixes: fa28237cfcc5 ("[POWERPC] Provide a way to protect 4k subpages when using 64k pages")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
[mpe: Rework into should_hash_preload() to avoid build fails w/SLICES=n]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index fbe747ed8c2d0c2d3ea7c469e231fb66edcd316e..59268969a0bc7b0d02e8c10b28f5b214f6209006 100644 (file)
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -1325,8 +1325,16 @@ int __hash_page(unsigned long ea, unsigned long msr, unsigned long trap,
 #ifdef CONFIG_PPC_MM_SLICES
 static bool should_hash_preload(struct mm_struct *mm, unsigned long ea)
 {
+       int psize = get_slice_psize(mm, ea);
+
        /* We only prefault standard pages for now */
-       if (unlikely(get_slice_psize(mm, ea) != mm->context.user_psize))
+       if (unlikely(psize != mm->context.user_psize))
+               return false;
+
+       /*
+        * Don't prefault if subpage protection is enabled for the EA.
+        */
+       if (unlikely((psize == MMU_PAGE_4K) && subpage_protection(mm, ea)))
                return false;
 
        return true;