kvm-84 + virtio Ubuntu Hardy guests

kvm-84 + virtio Ubuntu Hardy guests

[Dustin Kirkland]

Howdy kvm-

I'm receiving a heavy volume of Ubuntu Jaunty Beta users reporting
that Jaunty hosts running kvm-84 (userspace and kernel) are not able
to boot previously-working Hardy guests (2.6.24 kernel) if virtio
networking is enabled [1].  Users report that if e1000 is used
instead, the guest is able to boot (with degraded network performance,
obviously).  Users are also reporting that this was not a problem when
kvm-82 was used in Jaunty (though we also merged libvirt 0.5.1 up to
0.6.0 in roughly the same timeframe).

It's unclear to me, at this point, if this is a kvm or libvirt
problem.  I personally have not been able to reproduce this problem
with kvm alone.

However, I'm curious if anyone else here is familiar with this issue,
or has seen something similar?

[1] https://bugs.launchpad.net/ubuntu/+source/kvm/+bug/331128

Thanks,
-- 
:-Dustin

Re: kvm-84 + virtio Ubuntu Hardy guests

[Dustin Kirkland]

On Tue, Mar 31, 2009 at 5:28 PM, Dustin Kirkland <kirkland@canonical.com> wrote:
> I'm receiving a heavy volume of Ubuntu Jaunty Beta users reporting
> that Jaunty hosts running kvm-84 (userspace and kernel) are not able
> to boot previously-working Hardy guests (2.6.24 kernel) if virtio
> networking is enabled [1].  Users report that if e1000 is used
> instead, the guest is able to boot (with degraded network performance,
> obviously).  Users are also reporting that this was not a problem when
> kvm-82 was used in Jaunty (though we also merged libvirt 0.5.1 up to
> 0.6.0 in roughly the same timeframe).
...
> [1] https://bugs.launchpad.net/ubuntu/+source/kvm/+bug/331128

Howdy-

Just a follow-up...

Anthony was able to confirm this issue, and create a patch for KVM,
which we're carrying in Ubuntu.  It's a bit of a special-case hack,
but I'm dropping it here for the sake of completeness.

Basically, Hardy guests do not have working GSO (general segment
offload) support.  Some changes in kvm/libvirt appear to be exposing
this, and breaking some guests when running virtio.

This patch from Anthony basically disables this support in KVM
userspace (until we have a better solution for auto-detecting GSO
support or lack thereof).

:-Dustin

Work around broken virtio drivers in 2.6.26

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

diff --git a/qemu/hw/virtio-net.c b/qemu/hw/virtio-net.c
index 9bce3a0..5b615f9 100644
--- a/qemu/hw/virtio-net.c
+++ b/qemu/hw/virtio-net.c
@@ -120,6 +120,9 @@ static uint32_t virtio_net_get_features(VirtIODevice *vdev)

     if (tap_has_vnet_hdr(host)) {
         tap_using_vnet_hdr(host, 1);
+#if 0
+        /* Stop advertising advanced features until we work around the fact
+         * that this is totally broken in 2.6.26 kernels */
         features |= (1 << VIRTIO_NET_F_CSUM);
         features |= (1 << VIRTIO_NET_F_GUEST_CSUM);
         features |= (1 << VIRTIO_NET_F_GUEST_TSO4);
@@ -130,6 +133,7 @@ static uint32_t virtio_net_get_features(VirtIODevice *vdev)
         features |= (1 << VIRTIO_NET_F_HOST_ECN);
         features |= (1 << VIRTIO_NET_F_MRG_RXBUF);
         /* Kernel can't actually handle UFO in software currently. */
+#endif
     }
 #endif

@@ -374,8 +378,14 @@ static int receive_header(VirtIONet *n, struct
iovec *iov, int iovcnt,
     struct virtio_net_hdr *hdr = iov[0].iov_base;
     int offset = 0;

+#if 0
     hdr->flags = 0;
     hdr->gso_type = VIRTIO_NET_HDR_GSO_NONE;
+#else
+    /* we need to clear out the whole header, including any garbage that may be
+     */
+    memset(hdr, 0, sizeof(*hdr));
+#endif

 #ifdef TAP_VNET_HDR
     if (tap_has_vnet_hdr(n->vc->vlan->first_client)) {

Re: kvm-84 + virtio Ubuntu Hardy guests

[Mark McLoughlin]

On Mon, 2009-04-06 at 09:55 -0700, Dustin Kirkland wrote:
> On Tue, Mar 31, 2009 at 5:28 PM, Dustin Kirkland <kirkland@canonical.com> wrote:
> > I'm receiving a heavy volume of Ubuntu Jaunty Beta users reporting
> > that Jaunty hosts running kvm-84 (userspace and kernel) are not able
> > to boot previously-working Hardy guests (2.6.24 kernel) if virtio
> > networking is enabled [1].  Users report that if e1000 is used
> > instead, the guest is able to boot (with degraded network performance,
> > obviously).  Users are also reporting that this was not a problem when
> > kvm-82 was used in Jaunty (though we also merged libvirt 0.5.1 up to
> > 0.6.0 in roughly the same timeframe).
> ...
> > [1] https://bugs.launchpad.net/ubuntu/+source/kvm/+bug/331128
> 
> Howdy-
> 
> Just a follow-up...
> 
> Anthony was able to confirm this issue, and create a patch for KVM,
> which we're carrying in Ubuntu.  It's a bit of a special-case hack,
> but I'm dropping it here for the sake of completeness.
> 
> Basically, Hardy guests do not have working GSO (general segment
> offload) support.  Some changes in kvm/libvirt appear to be exposing
> this, and breaking some guests when running virtio.
> 
> This patch from Anthony basically disables this support in KVM
> userspace (until we have a better solution for auto-detecting GSO
> support or lack thereof).

The problem here is that 2.6.24/5 vintage guests are saying they support
something they don't. See this for further details:

http://lists.gnu.org/archive/html/qemu-devel/2009-01/msg00574.html

Cheers,
Mark.

Re: kvm-84 + virtio Ubuntu Hardy guests

[Dustin Kirkland]

On Mon, 2009-04-06 at 18:43 +0100, Mark McLoughlin wrote:
> The problem here is that 2.6.24/5 vintage guests are saying they
> support
> something they don't. See this for further details:
> 
> http://lists.gnu.org/archive/html/qemu-devel/2009-01/msg00574.html

Agreed, understood.  And those kernels should be patched.

However, it's a bit of a chicken/egg problem...  One can't even boot
those guests (with virtio) to update the kernel, as it panics on boot
(without the kvm hack).


:-Dustin

Re: kvm-84 + virtio Ubuntu Hardy guests

[Anthony Liguori]

Dustin Kirkland wrote:
> On Mon, 2009-04-06 at 18:43 +0100, Mark McLoughlin wrote:
>   
>> The problem here is that 2.6.24/5 vintage guests are saying they
>> support
>> something they don't. See this for further details:
>>
>> http://lists.gnu.org/archive/html/qemu-devel/2009-01/msg00574.html
>>     
>
> Agreed, understood.  And those kernels should be patched.
>
> However, it's a bit of a chicken/egg problem...  One can't even boot
> those guests (with virtio) to update the kernel, as it panics on boot
> (without the kvm hack).
>   

There's now a fix for this in QEMU stable.  It'll make it's way to 
kvm-userspace once Avi merges.

Regards,

Anthony Liguori
> :-Dustin
>
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