Re: Switching to user mode from domU kernel

[Trammell Hudson <hudson@osresearch.net>]

On Mon, Oct 22, 2007 at 09:12:05PM +0100, Keir Fraser wrote:
> On 22/10/07 20:52, "Trammell Hudson" <hudson@osresearch.net> wrote:
> > I've masked all events and the pending field in the shared_info
> > structure is zero.  There are no waiting characters in the incoming
> > xen_console->in_prod array.
> 
> Perhaps the page you think is shared_info isn't really? If Xen is calling
> you back repeatedly then it thinks events are pending.

That was it!  I had misunderstood the comment in the start_info
structure in xen.h:

    unsigned long shared_info;  /* MACHINE address of shared info struct. */
    xen_pfn_t store_mfn;        /* MACHINE page number of shared page.    */

I thought that the store_mfn was the machine page number for the
shared info structure and had used that as my xen_shared_info
pointer.  Mapping the address pointed to by shared_info instead
makes it work perfectly.

Now my kernel transfers into the user code and faults as expected.

Thank you!

-- Trammell