xtensa: fix fast_store_prohibited _PAGE_WRITABLE_BIT test

Before _PAGE_WRITABLE_BIT test fast_store_prohibited must make sure that
PTE is present. Otherwise 'writable' bit is undefined and may be reused
in the 'file offset' or 'swap type' PTE fields.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>

1 files changed, 6 insertions, 1 deletions

diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index 5082507d5631..fa94512ff84d 100644
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -1792,10 +1792,15 @@ ENTRY(fast_store_prohibited)
         l32i    a0, a0, 0
         beqz    a0, 2f
 
-        /* Note that we assume _PAGE_WRITABLE_BIT is only set if pte is valid.*/
+        /*
+         * Note that we test _PAGE_WRITABLE_BIT only if PTE is present
+         * and is not PAGE_NONE. See pgtable.h for possible PTE layouts.
+         */
 
         _PTE_OFFSET(a0, a1, a4)
         l32i    a4, a0, 0               # read pteval
+        movi    a1, _PAGE_CA_INVALID
+        ball    a4, a1, 2f
         bbci.l  a4, _PAGE_WRITABLE_BIT, 2f
 
         movi    a1, _PAGE_ACCESSED | _PAGE_DIRTY | _PAGE_HW_WRITE