Re: [PATCH] mmu notifiers #v5

[Andrea Arcangeli <andrea@qumranet.com>]

On Mon, Feb 04, 2008 at 11:09:01AM -0800, Christoph Lameter wrote:
> On Sun, 3 Feb 2008, Andrea Arcangeli wrote:
> 
> > > Right but that pin requires taking a refcount which we cannot do.
> > 
> > GRU can use my patch without the pin. XPMEM obviously can't use my
> > patch as my invalidate_page[s] are under the PT lock (a feature to fit
> > GRU/KVM in the simplest way), this is why an incremental patch adding
> > invalidate_range_start/end would be required to support XPMEM too.
> 
> Doesnt the kernel in some situations release the page before releasing the 
> pte lock? Then there will be an external pte pointing to a page that may 
> now have a different use. Its really bad if that pte does allow writes.

Sure the kernel does that most of the time, which is for example why I
had to use invalidate_page instead of invalidate_pages inside
zap_pte_range. Zero problems with that (this is also the exact reason
why I mentioned the tlb flushing code would need changes to convert
some page in pages).