powerpc: Fixes for CONFIG_PTE_64BIT for SMP support

There are some minor issues with support 64-bit PTEs on a 32-bit processor
when dealing with SMP.

* We need to order the stores in set_pte_at to make sure the flag word
  is set second.
* Change pte_clear to use pte_update so only the flag word is cleared
* Added a WARN_ON to set_pte_at to ensure the pte isn't present for
  the 64-bit pte/SMP case (to ensure our assumption of this fact).

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Acked-by: Becky Bruce <becky.bruce@freescale.com>

2 files changed, 21 insertions, 6 deletions

diff --git a/arch/powerpc/include/asm/highmem.h b/arch/powerpc/include/asm/highmem.h
index 5d99b6489d56..91c589520c0a 100644
--- a/arch/powerpc/include/asm/highmem.h
+++ b/arch/powerpc/include/asm/highmem.h
@@ -84,7 +84,7 @@ static inline void *kmap_atomic_prot(struct page *page, enum km_type type, pgpro
 #ifdef CONFIG_DEBUG_HIGHMEM
         BUG_ON(!pte_none(*(kmap_pte-idx)));
 #endif
-        set_pte_at(&init_mm, vaddr, kmap_pte-idx, mk_pte(page, prot));
+        __set_pte_at(&init_mm, vaddr, kmap_pte-idx, mk_pte(page, prot));
         flush_tlb_page(NULL, vaddr);
 
         return (void*) vaddr;
diff --git a/arch/powerpc/include/asm/pgtable-ppc32.h b/arch/powerpc/include/asm/pgtable-ppc32.h
index 6fe39e327047..1b1195555473 100644
--- a/arch/powerpc/include/asm/pgtable-ppc32.h
+++ b/arch/powerpc/include/asm/pgtable-ppc32.h
@@ -517,7 +517,8 @@ extern unsigned long bad_call_to_PMD_PAGE_SIZE(void);
 
 #define pte_none(pte)           ((pte_val(pte) & ~_PTE_NONE_MASK) == 0)
 #define pte_present(pte)        (pte_val(pte) & _PAGE_PRESENT)
-#define pte_clear(mm,addr,ptep) do { set_pte_at((mm), (addr), (ptep), __pte(0)); } while (0)
+#define pte_clear(mm, addr, ptep) \
+        do { pte_update(ptep, ~_PAGE_HASHPTE, 0); } while (0)
 
 #define pmd_none(pmd)           (!pmd_val(pmd))
 #define pmd_bad(pmd)            (pmd_val(pmd) & _PMD_BAD)
@@ -612,9 +613,6 @@ static inline unsigned long pte_update(pte_t *p,
         return old;
 }
 #else /* CONFIG_PTE_64BIT */
-/* TODO: Change that to only modify the low word and move set_pte_at()
- * out of line
- */
 static inline unsigned long long pte_update(pte_t *p,
                                             unsigned long clr,
                                             unsigned long set)
@@ -652,16 +650,33 @@ static inline unsigned long long pte_update(pte_t *p,
  * On machines which use an MMU hash table we avoid changing the
  * _PAGE_HASHPTE bit.
  */
-static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
+
+static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
                               pte_t *ptep, pte_t pte)
 {
 #if _PAGE_HASHPTE != 0
         pte_update(ptep, ~_PAGE_HASHPTE, pte_val(pte) & ~_PAGE_HASHPTE);
+#elif defined(CONFIG_PTE_64BIT) && defined(CONFIG_SMP)
+        __asm__ __volatile__("\
+                stw%U0%X0 %2,%0\n\
+                eieio\n\
+                stw%U0%X0 %L2,%1"
+        : "=m" (*ptep), "=m" (*((unsigned char *)ptep+4))
+        : "r" (pte) : "memory");
 #else
         *ptep = pte;
 #endif
 }
 
+static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
+                              pte_t *ptep, pte_t pte)
+{
+#if defined(CONFIG_PTE_64BIT) && defined(CONFIG_SMP)
+        WARN_ON(pte_present(*ptep));
+#endif
+        __set_pte_at(mm, addr, ptep, pte);
+}
+
 /*
  * 2.6 calls this without flushing the TLB entry; this is wrong
  * for our hash-based implementation, we fix that up here.