Re: [Xen-devel] Ubuntu 16.04.1 LTS kernel 4.4.0-57 over-allocation and xen-access fail

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/01/17 11:36, Razvan Cojocaru wrote:
> Hello,
>
> We've come across a weird phenomenon: an Ubuntu 16.04.1 LTS HVM guest
> running kernel 4.4.0 installed via XenCenter in XenServer Dundee seems
> to eat up all the RAM it can:
>
> (XEN) [  394.379760] d1v1 Over-allocation for domain 1: 524545 > 524544
>
> This leads to a problem with xen-access, specifically libxc which does
> this in xc_vm_event_enable() (this is Xen 4.6):
>
> ring_page = xc_map_foreign_batch(xch, domain_id, PROT_READ | PROT_WRITE,
>                                  &mmap_pfn, 1);
>
> if ( mmap_pfn & XEN_DOMCTL_PFINFO_XTAB )
> {
>     /* Map failed, populate ring page */
>     rc1 = xc_domain_populate_physmap_exact(xch, domain_id, 1, 0, 0,
>                                                &ring_pfn);
>     if ( rc1 != 0 )
>     {
>         PERROR("Failed to populate ring pfn\n");
>         goto out;
>     }
>
> The first time everything works fine, xen-access can map the ring page.
> But most of the time the second time fails in the
> xc_domain_populate_physmap_exact() call, and again this is dumped in the
> Xen log (once for each failed attempt):
>
> (XEN) [  395.952188] d0v3 Over-allocation for domain 1: 524545 > 524544

Thinking further about this, what happens if you avoid removing the page
on exit?

The first populate succeeds, and if you leave the page populated, the
second time you come around the loop, it should not be of type XTAB, and
the map should succeed.

~Andrew

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel