Re: [patch, feature] nonlinear mappings, prefaulting support, 2.5.42-F8

William Lee Irwin III
2002-10-14T21:20:45Z

On Mon, Oct 14, 2002 at 06:02:30PM +0200, Ingo Molnar wrote:
>> if this is really an issue then we could force vma->vm_page_prot to
>> PROT_NONE within remap_file_pages(), so at least all subsequent faults
>> will be PROT_NONE and the user would have to explicitly re-mprotect()
>> the vma again to change this.
> i've added this to the -G1 patch at:
> http://redhat.com/~mingo/remap-file-pages-patches/
> Ingo

Also, this may be relaxed when the file offsets match.
Against unpatched -G1:

Bill

--- mpop-2.5.42/mm/fremap.c 2002-10-14 11:43:03.000000000 -0700
+++ wlipop-2.5.42/mm/fremap.c 2002-10-14 14:17:11.000000000 -0700
@@ -129,10 +129,16 @@
end > start && start >= vma->vm_start &&
end <= vma->vm_end) {
/*
- * Change the default protection to PROT_NONE:
+ * Change the default protection to PROT_NONE if
+ * the file offset doesn't coincide with the vma's:
*/
- if (pgprot_val(vma->vm_page_prot) != pgprot_val(__S000))
- vma->vm_page_prot = __S000;
+ if (pgprot_val(vma->vm_page_prot) != pgprot_val(__S000)) {
+ unsigned long offset;
+ offset = (start - vma->vm_start) >> PAGE_CACHE_SHIFT
+ + vma->vm_pgoff;
+ if (offset != pgoff)
+ vma->vm_page_prot = __S000;
+ }
err = vma->vm_ops->populate(vma, start, size, prot,
pgoff, flags & MAP_NONBLOCK);
}