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authorBenjamin Herrenschmidt <benh@kernel.crashing.org>2010-07-23 09:02:27 +1000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2010-07-23 12:55:21 +1000
commit171aa2caaad16ed32b655d33565e112a12cb3537 (patch)
treefcaff760d9771e932fbfe831a3fc1ce4dc0bce00
parentca91e6c09d656c6deb1f2bc5d57186c718106aa5 (diff)
powerpc/mm: Fix bugs in huge page hashing
There's a couple of nasty bugs lurking in our huge page hashing code. First, we don't check the access permission atomically with setting the _PAGE_BUSY bit, which means that the PTE value we end up using for the hashing might be different than the one we have checked the access permissions for. We've seen cases where that leads us to try to use an invalidated PTE for hashing, causing all sort of "interesting" issues. Then, we also failed to set _PAGE_DIRTY on a write access. Finally, a minor tweak but we should return 0 when we find the PTE busy, in order to just re-execute the access, rather than 1 which means going to do_page_fault(). Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> ---
-rw-r--r--arch/powerpc/mm/hugetlbpage-hash64.c31
1 files changed, 13 insertions, 18 deletions
diff --git a/arch/powerpc/mm/hugetlbpage-hash64.c b/arch/powerpc/mm/hugetlbpage-hash64.c
index c9acd7910ee..faae9ec4cb0 100644
--- a/arch/powerpc/mm/hugetlbpage-hash64.c
+++ b/arch/powerpc/mm/hugetlbpage-hash64.c
@@ -21,21 +21,13 @@ int __hash_page_huge(unsigned long ea, unsigned long access, unsigned long vsid,
unsigned long old_pte, new_pte;
unsigned long va, rflags, pa, sz;
long slot;
- int err = 1;
BUG_ON(shift != mmu_psize_defs[mmu_psize].shift);
/* Search the Linux page table for a match with va */
va = hpt_va(ea, vsid, ssize);
- /*
- * Check the user's access rights to the page. If access should be
- * prevented then send the problem up to do_page_fault.
- */
- if (unlikely(access & ~pte_val(*ptep)))
- goto out;
- /*
- * At this point, we have a pte (old_pte) which can be used to build
+ /* At this point, we have a pte (old_pte) which can be used to build
* or update an HPTE. There are 2 cases:
*
* 1. There is a valid (present) pte with no associated HPTE (this is
@@ -49,9 +41,17 @@ int __hash_page_huge(unsigned long ea, unsigned long access, unsigned long vsid,
do {
old_pte = pte_val(*ptep);
- if (old_pte & _PAGE_BUSY)
- goto out;
+ /* If PTE busy, retry the access */
+ if (unlikely(old_pte & _PAGE_BUSY))
+ return 0;
+ /* If PTE permissions don't match, take page fault */
+ if (unlikely(access & ~old_pte))
+ return 1;
+ /* Try to lock the PTE, add ACCESSED and DIRTY if it was
+ * a write access */
new_pte = old_pte | _PAGE_BUSY | _PAGE_ACCESSED;
+ if (access & _PAGE_RW)
+ new_pte |= _PAGE_DIRTY;
} while(old_pte != __cmpxchg_u64((unsigned long *)ptep,
old_pte, new_pte));
@@ -127,8 +127,7 @@ repeat:
*/
if (unlikely(slot == -2)) {
*ptep = __pte(old_pte);
- err = -1;
- goto out;
+ return -1;
}
new_pte |= (slot << 12) & (_PAGE_F_SECOND | _PAGE_F_GIX);
@@ -138,9 +137,5 @@ repeat:
* No need to use ldarx/stdcx here
*/
*ptep = __pte(new_pte & ~_PAGE_BUSY);
-
- err = 0;
-
- out:
- return err;
+ return 0;
}