Re: [Xen-devel] [PATCH] Allow programatic iomem permissions

[Kieran Mansley <kmansley@xxxxxxxxxxxxxx>]

On Fri, 2007-07-13 at 13:29 +0100, Keir Fraser wrote:
> 
> 
> On 13/7/07 12:05, "Kieran Mansley" <kmansley@xxxxxxxxxxxxxx> wrote:
> 
> > Any thoughts on the above?
> > 
> > I'm happy to do some work to rectify this situation but don't want to
> > expend effort on something that won't get accepted.  Any background on
> > the reasons for the restriction (i.e. what the TLB flushing issues are)
> > would also be of help.
> 
> The issue is that the granter is informed that the grant is released before
> stale grantee TLB entries are flushed. If the grantee is multi-vcpu then he
> could theoretically still access a granted page via a stale TLB entry after
> the granter has recycled the page. The window is extremely tiny though! The
> correct fix is to reorder the unmap operation to be unmap-list-of-grants
> then TLB-flush then update-grant-entries-to-indicate-release. Then the whole
> problem disappears.

OK, that makes sense, and doesn't at first impression look too hard to
rectify.

Am I right in thinking that it's the shared grant table entry that is
the critical one in this sense (as opposed to the "active" entry).

Kieran


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel