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authorMike Frysinger <vapier.adi@gmail.com>2010-01-06 17:23:23 +0000
committerLinus Torvalds <torvalds@linux-foundation.org>2010-01-06 18:16:02 -0800
commitcfe79c00a2f4f687eed8b7534d1d3d3d35540c29 (patch)
tree62c603938e7b740ca16ce1012a6ee7ab08b3f727 /mm/nommu.c
parent04e4f2b18c8de1389d1e00fef0f42a8099910daf (diff)
downloadvexpress-lsk-cfe79c00a2f4f687eed8b7534d1d3d3d35540c29.tar.gz
NOMMU: Avoiding duplicate icache flushes of shared maps
When working with FDPIC, there are many shared mappings of read-only code regions between applications (the C library, applet packages like busybox, etc.), but the current do_mmap_pgoff() function will issue an icache flush whenever a VMA is added to an MM instead of only doing it when the map is initially created. The flush can instead be done when a region is first mmapped PROT_EXEC. Note that we may not rely on the first mapping of a region being executable - it's possible for it to be PROT_READ only, so we have to remember whether we've flushed the region or not, and then flush the entire region when a bit of it is made executable. However, this also affects the brk area. That will no longer be executable. We can mprotect() it to PROT_EXEC on MPU-mode kernels, but for NOMMU mode kernels, when it increases the brk allocation, making sys_brk() flush the extra from the icache should suffice. The brk area probably isn't used by NOMMU programs since the brk area can only use up the leavings from the stack allocation, where the stack allocation is larger than requested. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Mike Frysinger <vapier@gentoo.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/nommu.c')
-rw-r--r--mm/nommu.c11
1 files changed, 8 insertions, 3 deletions
diff --git a/mm/nommu.c b/mm/nommu.c
index 6f9248f89bd..a8d17521624 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -432,6 +432,7 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
/*
* Ok, looks good - let it rip.
*/
+ flush_icache_range(mm->brk, brk);
return mm->brk = brk;
}
@@ -1353,10 +1354,14 @@ unsigned long do_mmap_pgoff(struct file *file,
share:
add_vma_to_mm(current->mm, vma);
- up_write(&nommu_region_sem);
+ /* we flush the region from the icache only when the first executable
+ * mapping of it is made */
+ if (vma->vm_flags & VM_EXEC && !region->vm_icache_flushed) {
+ flush_icache_range(region->vm_start, region->vm_end);
+ region->vm_icache_flushed = true;
+ }
- if (prot & PROT_EXEC)
- flush_icache_range(result, result + len);
+ up_write(&nommu_region_sem);
kleave(" = %lx", result);
return result;