From: Paolo 'Blaisorblade' Giarrusso <[email protected]>
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 <[email protected]>
---
mm/fremap.c | 27 ++++++++++++++-------------
1 files changed, 14 insertions(+), 13 deletions(-)
diff --git a/mm/fremap.c b/mm/fremap.c
index b1db410..3438caf 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -213,8 +213,9 @@ 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) {
@@ -231,19 +232,19 @@ 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,
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