Re: [Xen-devel] HVM pvops failures (one more qemu-dm.strace obtained)

[Boris Derzhavets <bderzhavets@xxxxxxxxx>]

Ping is based on ICMP.

 TCP (UDP) services might fail to reach the host.
 Failure of cheksum offloading on the second host may be the first example.
 But here it doesn't seem to be the case.
"tcpdump" on Xen host may help after issue comes up.
 See what happens to ssh packages when they arrive.

Boris.
 

--- On Wed, 3/18/09, Andrew Lyon <andrew.lyon@xxxxxxxxx> wrote:

From: Andrew Lyon <andrew.lyon@xxxxxxxxx>
Subject: Re: [Xen-devel] HVM pvops failures (one more qemu-dm.strace obtained)
To: "Jeremy Fitzhardinge" <jeremy@xxxxxxxx>
Cc: "Ian Campbell" <Ian.Campbell@xxxxxxxxxxxxx>, "Boris Derzhavets" <bderzhavets@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Ian Jackson" <Ian.Jackson@xxxxxxxxxxxxx>
Date: Wednesday, March 18, 2009, 4:17 AM

On Tue, Mar 3, 2009 at 5:41 PM, Jeremy Fitzhardinge <jeremy@xxxxxxxx>
wrote:
> Andrew Lyon wrote:
>>
>> On Thu, Feb 26, 2009 at 11:35 AM, Ian Jackson
<Ian.Jackson@xxxxxxxxxxxxx>
>> wrote:
>>
>>>
>>> Jeremy Fitzhardinge writes ("Re: [Xen-devel] HVM pvops
failures (one more
>>> qemu-dm.strace obtained)"):
>>>
>>>>
>>>> I was hoping Ian J would pop up and say "Its broken like
this!  Fix it
>>>> like this!".
>>>>
>>>
>>> Yes, when I have a moment I'll try it myself but I've been
buried in
>>> the bowels of a nightmare USB emulation.  Soon I'll know
whether the
>>> latter works and
 thus whether I have any time to dig into pvops.
>>>
>>> Ian.
>>>
>>>
>>
>> Has anybody made any progress on the qemu-dm / hvm issue with pv_ops?
>> I spent most of yesterday going through the strace logs but I cannot
>> see why it fails as it does.
>>
>
> Thanks for looking into this.  The crash is a SIGBUS in qemu, shortly
after
> an mmap of /proc/xen/privcmd, which is a suspicious combination.  The
SIGBUS
> means we managed to create a mapping where the kernel thinks there are no
> backing pages (at least in part).  It would be useful to know if any
memory
> accesses to the privcmd mapping succeed, and what the offset of the
failing
> one is.  (Assuming the SIGBUS is related to a privcmd mapping at all.)
>
> I don't think privcmd mappings can be completely broken, because
 the
qemu
> backend for pvfb works fine, and I assume that uses that path to map the
> framebuffer...
>
> Also, have you tried using stub domains?  They should have no dependence
on
> the dom0 kernel at all, so in theory they should work regardless.
>
>   J
>

I tried Stub domains yesterday but as soon as I "xm create" the
system
locked up, I could still ping it but no response on the serial console
and ssh was responsive, very strange.. I've never seen a system ping
but have unresponsive console.

Can we try to debug the problem with hvm on pv_ops?

Andy

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