Re: [Xen-ia64-devel] iosapic virtualisation

[Alex Williamson <alex.williamson@xxxxxx>]

On Wed, 2006-02-01 at 10:11 +0100, Tristan Gingold wrote:
> Le Mardi 31 Janvier 2006 20:53, Alex Williamson a écrit :

> >       * Assigning vectors as defined by the domain; I think this is
> >         covered by some of the comments included about future problems,
> >         but maybe we should address this one now.  We should probably
> >         start out with separate vector spaces between xen and each
> >         domain and keep a mapping table between xen vectors (ie. what's
> >         actually programmed into the IOSAPIC RTE) and what the domains
> >         tried to program via iosapic_guest_write().  It's probably
> >         reasonable to assign xen vectors from highest to lowest such
> >         that xen will end up with the highest priority external
> >         interrupts, dom0 the next highest, and so on.
> I don't really understand your point here.
> With the patch there is no relations between IOSAPIC vector and domain 
> vector.  
> That's the reason why there is an heavy weight look-up.  If we create a 
> look-up table (see previous point), we do what you describe here, don't we ?

   Ah, I see it now.  I missed how we're ignoring the vector from the
domain when we call iosapic_register_intr() then we store it in rte->vec
for the call back to the domain.  Perfect.

> >       * We need to paravirtualize reads of the IOSAPIC as well as
> >         writes.  Since the IOSAPICs use a windowing register scheme, a
> >         domain reading an IOSAPIC could interfere with Xen writing or
> >         cause races with other domains.  This will also enable us to
> >         hide the physical IOSAPIC structure if we need to at some point.
> Ok.  I think this point is rather moot because linux doesn't read IOSAPIC 
> (except version, which is not windowed).  However for completion I will do 
> it.

  Doesn't iosapic_version() call iosapic_read() which writes to the
IOSAPIC_REG_SELECT register?  I was concerned that's where we'd run into
a problem, but maybe I'm forgetting something about how IOSAPICs work.
By the way, I don't see iosapic.h in the patch set, probably why it
didn't compile for me.  Thanks,

        Alex

-- 
Alex Williamson                             HP Linux & Open Source Lab


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