Re: [Xen-devel] Grant tables from dom0 userspace?

["Andrew Warfield" <andrew.warfield@xxxxxxxxxxxx>]

Hi Steven,

> I've hacked around many of
> the problems, such as implicit unmapping of grant references, but others
> remain.  Some of the issues have no resolution in the grant table
> architecture.

   It would be quite useful to know what specific problems you have
encountered in this effort as insight for future versions of the code.
 The main problem that I have encountered in user-level foreign page
mappings is (as discussed previously) that Linux is a bit hasty in
blowing away user virtual memory areas, and doesn't provide a good
mechanism to safely unmap the pages.  The kernel has all the
information it needs to do the right thing though, and I think this
should be reasonably fixed in the future -- i don't see a compelling
reason for Xen to do extra book-keeping to cover for something that
the OS could just as easily do.  Especially for something like
cross-VM mappings, which don't exist in the non-virtualized system. 
Are there implicit unmapping problems that you thing would remain
unsolved if, for instance, there was a vm area destructor early enough
to allow the OS to properly unmap active grants?

   When you say, "others remain," can you provide a little more detail?

thanks!
a.

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