Re: [RFCv1 7/7] KVM: unmap guest memory using poisoned pages

[Kirill A. Shutemov]

On Fri, Apr 09, 2021 at 03:50:42PM +0200, David Hildenbrand wrote:
> > > 3. Allow selected users to still grab the pages (esp. KVM to fault them into
> > > the page tables).
> > 
> > As long as fault leads to non-present PTEs we are fine. Usespace still may
> > want to mlock() some of guest memory. There's no reason to prevent this.
> 
> I'm curious, even get_user_pages() will lead to a present PTE as is, no? So
> that will need modifications I assume. (although I think it fundamentally
> differs to the way get_user_pages() works - trigger a fault first, then
> lookup the PTE in the page tables).

For now, the patch has two step poisoning: first fault in, on the add to
shadow PTE -- poison. By the time VM has chance to use the page it's
poisoned and unmapped from the host userspace.

-- 
 Kirill A. Shutemov