Re: [PATCH] mm: mmu_notifier: fix inconsistent memory between secondary MMU and host

Hugh Dickins
2012-08-22T04:12:09Z

On Wed, 22 Aug 2012, Xiao Guangrong wrote:
> On 08/21/2012 11:06 PM, Andrea Arcangeli wrote:
> >
> > The KSM usage of it looks safe because it will only establish readonly
> > ptes with it.
>
> Hmm, in KSM code, i found this code in replace_page:
>
> set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
>
> It is possible to establish a writable pte, no?

No: we only do KSM in private vmas (!VM_SHARED), and because of the
need to CopyOnWrite in those, vm_page_prot excludes write permission:
write permission has to be added on COW fault.

Hugh