[PATCH] update_mmu_cache: Don't dcbst non-readable pages.

Currently, update_mmu_cache will crash if given a no-access PTE.  There's no
need to synchronize dcache/icache unless it's an exec mapping -- however,
due to the existence of older glibc versions that execute out of a
read-but-no-exec page, readability is tested instead.

This assumes no exec-only mappings; if such mappings become supported, they
will need to go through the kmap_atomic() version of dcache/icache
synchronization.

Signed-off-by: Scott Wood <redacted>
---
This fixes the following bug:
http://ozlabs.org/pipermail/linuxppc-dev/2008-February/051080.html

 arch/powerpc/mm/mem.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index e812244..c7d7bd4 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c

@@ -483,7 +483,12 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
 		 */
 		_tlbie(address, 0 /* 8xx doesn't care about PID */);
 #endif
-		if (!PageReserved(page)
+		/* The _PAGE_USER test should really be _PAGE_EXEC, but
+		 * older glibc versions execute some code from no-exec
+		 * pages, which for now we are supporting.  If exec-only
+		 * pages are ever implemented, this will have to change.
+		 */
+		if (!PageReserved(page) && (pte_val(pte) & _PAGE_USER)
 		    && !test_bit(PG_arch_1, &page->flags)) {
 			if (vma->vm_mm == current->active_mm) {
 				__flush_dcache_icache((void *) address);

-- 
1.5.3.8

On Tue, 2008-02-05 at 13:43 -0600, Scott Wood wrote:

Currently, update_mmu_cache will crash if given a no-access PTE.  There's no
need to synchronize dcache/icache unless it's an exec mapping -- however,
due to the existence of older glibc versions that execute out of a
read-but-no-exec page, readability is tested instead.

This assumes no exec-only mappings; if such mappings become supported, they
will need to go through the kmap_atomic() version of dcache/icache
synchronization.

Signed-off-by: Scott Wood <redacted>

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>