Re: [Xen-devel] blkif_map error starting fourth guest domain

[Kieran Mansley <kmansley@xxxxxxxxxxxxxx>]

On Fri, 2007-06-08 at 11:19 +0100, Kieran Mansley wrote:
> On Thu, 2007-06-07 at 16:12 +0100, Keir Fraser wrote:
> > 
> > 
> > On 7/6/07 16:06, "Kieran Mansley" <kmansley@xxxxxxxxxxxxxx> wrote:
> > 
> > > The reason for blkif_map() failing seems to be the map_frontend_page()
> > > call failing.
> > > 
> > > xm dmesg prints out:
> > > (XEN) mm.c:2610:d0 Could not find L1 PTE for address e1204000
> > > which seems likely to be connected to map_frontend_page() failing.
> > 
> > Yes, this is the problem. You'll need to add some more tracing, find out
> > exactly which grant_map operation issued by dom0 is failing, and find out
> > why Xen thinks there is no pte mapping the specified virtual address.
> 
> The grant map that's failing is (linux-2.6-xen-
> sparse/drivers/xen/blkback/interface.c:62):
> 
>       gnttab_set_map_op(&op, (unsigned long)blkif->blk_ring_area->addr,
>                         GNTMAP_host_map, shared_page, blkif->domid);
> 
>       if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
>               BUG();
> 
> I'll get some more tracing and info about why this page supplied by the
> frontend doesn't have a PTE when I get some spare time.
> 
> Kieran

By way of a follow-up, I'm no longer able to reproduce this.  It now
works fine, and has done for some time.  I suspect it may have been due
to the bug/fix alluded to in this:

http://lists.xensource.com/archives/html/xen-devel/2007-07/msg00402.html

It doesn't fit with that perfectly, so it may be the problem is
different (and still there) but if it reappears I'll let you know.

Kieran


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