Re: [PATCH] restore protections after forced fault in get_user_pages

[Roland McGrath <roland@redhat.com>]

> The follow_page issue should be fixable by just marking the _page_ dirty 
> inside the ptrace routines. I think we do that anyway (or we'd already be 
> buggy wrt perfectly normal writes).

access_process_vm already calls set_page_dirty_locked, in fact.
So things are relatively simple.

I suggested using pte_modify(pte, vma->vm_page_prot).  That is not the
right thing to do, in fact.  For private mappings, the vm_page_prot value
is always unwritable (PAGE_COPY).  So getting the right bits is tiny bit
hairier.  Either it can do:

	if (vma->vm_flags & VM_WRITE)
		entry = pte_mkwrite(entry);

or it can do something branchless like:

	entry = pte_modify(entry, protection_map[vma->vm_flags & 0x7]);

Or maybe there is a more optimal formulation I haven't thought of.


Thanks,
Roland