[PATCH] mm: parisc pte atomicity

There's a worrying function translation_exists in parisc cacheflush.h,
unaffected by split ptlock since flush_dcache_page is using it on some other
mm, without any relevant lock.  Oh well, make it a slightly more robust by
factoring the pfn check within it.  And it looked liable to confuse a
camouflaged swap or file entry with a good pte: fix that too.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/parisc/kernel/cache.c b/arch/parisc/kernel/cache.c
index e15f09e..a065349 100644 (file)
--- a/arch/parisc/kernel/cache.c
+++ b/arch/parisc/kernel/cache.c
@@ -270,7 +270,6 @@ void flush_dcache_page(struct page *page)
        unsigned long offset;
        unsigned long addr;
        pgoff_t pgoff;
-       pte_t *pte;
        unsigned long pfn = page_to_pfn(page);
 
 
@@ -301,21 +300,16 @@ void flush_dcache_page(struct page *page)
                 * taking a page fault if the pte doesn't exist.
                 * This is just for speed.  If the page translation
                 * isn't there, there's no point exciting the
-                * nadtlb handler into a nullification frenzy */
-
-
-               if(!(pte = translation_exists(mpnt, addr)))
-                       continue;
-
-               /* make sure we really have this page: the private
+                * nadtlb handler into a nullification frenzy.
+                *
+                * Make sure we really have this page: the private
                 * mappings may cover this area but have COW'd this
-                * particular page */
-               if(pte_pfn(*pte) != pfn)
-                       continue;
-
-               __flush_cache_page(mpnt, addr);
-
-               break;
+                * particular page.
+                */
+               if (translation_exists(mpnt, addr, pfn)) {
+                       __flush_cache_page(mpnt, addr);
+                       break;
+               }
        }
        flush_dcache_mmap_unlock(mapping);
 }

diff --git a/include/asm-parisc/cacheflush.h b/include/asm-parisc/cacheflush.h
index aa592d8..1bc3c83 100644 (file)
--- a/include/asm-parisc/cacheflush.h
+++ b/include/asm-parisc/cacheflush.h
@@ -100,30 +100,34 @@ static inline void flush_cache_range(struct vm_area_struct *vma,
 
 /* Simple function to work out if we have an existing address translation
  * for a user space vma. */
-static inline pte_t *__translation_exists(struct mm_struct *mm,
-                                         unsigned long addr)
+static inline int translation_exists(struct vm_area_struct *vma,
+                               unsigned long addr, unsigned long pfn)
 {
-       pgd_t *pgd = pgd_offset(mm, addr);
+       pgd_t *pgd = pgd_offset(vma->vm_mm, addr);
        pmd_t *pmd;
-       pte_t *pte;
+       pte_t pte;
 
        if(pgd_none(*pgd))
-               return NULL;
+               return 0;
 
        pmd = pmd_offset(pgd, addr);
        if(pmd_none(*pmd) || pmd_bad(*pmd))
-               return NULL;
+               return 0;
 
-       pte = pte_offset_map(pmd, addr);
+       /* We cannot take the pte lock here: flush_cache_page is usually
+        * called with pte lock already held.  Whereas flush_dcache_page
+        * takes flush_dcache_mmap_lock, which is lower in the hierarchy:
+        * the vma itself is secure, but the pte might come or go racily.
+        */
+       pte = *pte_offset_map(pmd, addr);
+       /* But pte_unmap() does nothing on this architecture */
 
-       /* The PA flush mappings show up as pte_none, but they're
-        * valid none the less */
-       if(pte_none(*pte) && ((pte_val(*pte) & _PAGE_FLUSH) == 0))
-               return NULL;
-       return pte;
-}
-#define        translation_exists(vma, addr)   __translation_exists((vma)->vm_mm, addr)
+       /* Filter out coincidental file entries and swap entries */
+       if (!(pte_val(pte) & (_PAGE_FLUSH|_PAGE_PRESENT)))
+               return 0;
 
+       return pte_pfn(pte) == pfn;
+}
 
 /* Private function to flush a page from the cache of a non-current
  * process.  cr25 contains the Page Directory of the current user
@@ -175,9 +179,8 @@ flush_cache_page(struct vm_area_struct *vma, unsigned long vmaddr, unsigned long
 {
        BUG_ON(!vma->vm_mm->context);
 
-       if(likely(translation_exists(vma, vmaddr)))
+       if (likely(translation_exists(vma, vmaddr, pfn)))
                __flush_cache_page(vma, vmaddr);
 
 }
 #endif
-