powerpc: Add 64 bit version of huge_ptep_set_wrprotect

The implementation of huge_ptep_set_wrprotect() directly calls
ptep_set_wrprotect() to mark a hugepte write protected.  However this
call is not appropriate on ppc64 kernels as this is a small page only
implementation.  This can lead to the hash not being flushed correctly
when a mapping is being converted to COW, allowing processes to continue
using the original copy.

Currently huge_ptep_set_wrprotect() unconditionally calls
ptep_set_wrprotect().  This is fine on ppc32 kernels as this call is
generic.  On 64 bit this is implemented as:

	pte_update(mm, addr, ptep, _PAGE_RW, 0);

On ppc64 this last parameter is the page size and is passed directly on
to hpte_need_flush():

	hpte_need_flush(mm, addr, ptep, old, huge);

And this directly affects the page size we pass to flush_hash_page():

	flush_hash_page(vaddr, rpte, psize, ssize, 0);

As this changes the way the hash is calculated we will flush the wrong
pages, potentially leaving live hashes to the original page.

Move the definition of huge_ptep_set_wrprotect() to the 32/64 bit specific
headers.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/include/asm-powerpc/pgtable-ppc64.h b/include/asm-powerpc/pgtable-ppc64.h
index 2e48be841cc9..b2754d46be44 100644
--- a/include/asm-powerpc/pgtable-ppc64.h
+++ b/include/asm-powerpc/pgtable-ppc64.h
@@ -312,6 +312,15 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr,
                 return;
         old = pte_update(mm, addr, ptep, _PAGE_RW, 0);
 }
+static inline void huge_ptep_set_wrprotect(struct mm_struct *mm,
+                                           unsigned long addr, pte_t *ptep)
+{
+        unsigned long old;
+
+        if ((pte_val(*ptep) & _PAGE_RW) == 0)
+                return;
+        old = pte_update(mm, addr, ptep, _PAGE_RW, 1);
+}
 
 /*
  * We currently remove entries from the hashtable regardless of whether