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From: | Alexander Graf |
Subject: | [Qemu-devel] Re: virtio breakage with 2.6.25 guest kernel |
Date: | Tue, 13 Jan 2009 22:05:30 +0100 |
On 13.01.2009, at 21:14, Anthony Liguori <address@hidden> wrote:
Alexander Graf wrote:Hi,while I don't fully understand the problem, here's what I experience so far:When using an openSUSE 11.0 kernel (2.6.25) in the guest, virtio on tapbreaks with current KVM git, while it used to work before (haven'tbisected, definitely worked in kvm-78, but is probably due to Anthony'srewrite). It shows the following message (comes from qemu):There were a couple of old-guest-breaking regressions. I think we've fixed all of them but there could be more. Are you using the latest kvm-userspace?
This one is definitely due to the broken guest kernel. I applied the patch mark mentioned to ours and things started working.
So the only way I can think of to 'fix' it is by detecting broken guests. We could supply a host mask of 0xffffffff and see if tge guest feature mask is tge same. If so, feature masking is probably broken.
Alex
Regards, Anthony Liguorivirtio-net header not in first element This is because qemu expects a message with mergeable rx bufs (12 bytes), but if I see things correctly the old kernel doesn't support that feature (sends 10 bytes). I put in some debug messages on IO reads/writes in the qemu virtio handler and got these: virtio IO read: 0 = 0x100bba3 virtio IO write: 0x4 = 0x100bba3 virtio: setting features 0x100bba3 So I believe the feature masking is somewhat non-functional? Or did I read the masking code in qemu's virtio-net wrong? Basically for me, current KVM git broke old guest support, which is aclear regression and should not happen. Does anybody with more expertisein virtio want to take on this? Alex
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