[patch 12/14] remap_file_pages protection support: also set VM_NONLINEAR on nonuniform VMAs

From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@xxxxxxxx>

To simplify the VM code, and to reflect expected application usage, we decide
to also set VM_NONLINEAR when setting VM_MANYPROTS. Otherwise, we'd have to
possibly save nonlinear PTEs even on paths which cope with linear VMAs. It's
possible, but intrusive (it's done in one of the next patches).

Obviously, this has a performance cost, since we potentially have to handle a
linear VMA with nonlinear handling code. But I didn't know of any application
which might have this usage.

XXX: update: glibc wants to replace mprotect() with linear VM_MANYPROTS areas,
to handle guard pages and data mappings of shared objects.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@xxxxxxxx>
Index: linux-2.6.git/mm/fremap.c
===================================================================
--- linux-2.6.git.orig/mm/fremap.c
+++ linux-2.6.git/mm/fremap.c
@@ -206,8 +206,9 @@ retry:

if (!vma->vm_private_data || (vma->vm_flags & VM_NONLINEAR)) {
/* Must set VM_NONLINEAR before any pages are populated. */
- if (pgoff != linear_page_index(vma, start) &&
- !(vma->vm_flags & VM_NONLINEAR)) {
+ if (!(vma->vm_flags & VM_NONLINEAR) &&
+ (pgoff != linear_page_index(vma, start) ||
+ pgprot_val(pgprot) != pgprot_val(vma->vm_page_prot))) {
if (!(vma->vm_flags & VM_SHARED))
goto out_unlock;
if (!has_write_lock) {
@@ -224,19 +225,19 @@ retry:
vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
flush_dcache_mmap_unlock(mapping);
spin_unlock(&mapping->i_mmap_lock);
- }

- if (pgprot_val(pgprot) != pgprot_val(vma->vm_page_prot) &&
- !(vma->vm_flags & VM_MANYPROTS)) {
- if (!(vma->vm_flags & VM_SHARED))
- goto out_unlock;
- if (!has_write_lock) {
- up_read(&mm->mmap_sem);
- down_write(&mm->mmap_sem);
- has_write_lock = 1;
- goto retry;
+ if (!(vma->vm_flags & VM_MANYPROTS) &&
+ pgprot_val(pgprot) != pgprot_val(vma->vm_page_prot)) {
+ if (!(vma->vm_flags & VM_SHARED))
+ goto out_unlock;
+ if (!has_write_lock) {
+ up_read(&mm->mmap_sem);
+ down_write(&mm->mmap_sem);
+ has_write_lock = 1;
+ goto retry;
+ }
+ vma->vm_flags |= VM_MANYPROTS;
}
- vma->vm_flags |= VM_MANYPROTS;
}

err = vma->vm_ops->populate(vma, start, size, pgprot, pgoff,

--
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade
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