differences in hvm save/restore in 3.1 vs 3.2

differences in hvm save/restore in 3.1 vs 3.2

[James Harper]

I'm still trying to figure out why save/restore was working with my
windows gplpv drivers and suddenly now it's not, and I've just realised
that the one thing that has changed is that I've switched back to Xen
3.2 again, and when it was working I was using Xen 3.1.

Are there any fundamental differences between how the HVM save/restore
works between 3.1 and 3.2?

It seems I can't use the windows debugger to help me, as after I restore
it will no longer reconnect, while it did when I was using Xen 3.1. That
may be unrelated to the above problem though... the debugger connects to
the serial port of the hvm domain via an 'xm console xxx' command in
inetd.conf... and I think that that isn't working properly after the
restore.

Thanks

James

RE: differences in hvm save/restore in 3.1 vs 3.2

[James Harper]

> 
> It seems I can't use the windows debugger to help me, as after I
restore
> it will no longer reconnect, while it did when I was using Xen 3.1.
That
> may be unrelated to the above problem though... the debugger connects
to
> the serial port of the hvm domain via an 'xm console xxx' command in
> inetd.conf... and I think that that isn't working properly after the
> restore.

Further to this, before the 'save' is issued, 'xm console' behaves how I
would expect - nothing gets echo's to the screen and ^] closes the
console session. After the 'restore', 'xm console' echo's everything to
the screen, and ^] doesn't do anything useful (apart from print ^] on
the screen), like the console session hasn't connected to the serial
port at all.

Any idea's on that?

Thanks

James

Re: differences in hvm save/restore in 3.1 vs 3.2

[Christopher Head]

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There's a bug in the serial port emulation in qemu related to saving and
restoring. There's a patch floating around somewhere which fixes it, but
depending on what source tree you're using you may not have it yet. One
of the critical registers isn't saved and also isn't regenerated at
restore time, meaning that serial port interrupts stop getting delivered
to the guest properly.

Chris

James Harper wrote:
|> It seems I can't use the windows debugger to help me, as after I
| restore
|> it will no longer reconnect, while it did when I was using Xen 3.1.
| That
|> may be unrelated to the above problem though... the debugger connects
| to
|> the serial port of the hvm domain via an 'xm console xxx' command in
|> inetd.conf... and I think that that isn't working properly after the
|> restore.
|
| Further to this, before the 'save' is issued, 'xm console' behaves how I
| would expect - nothing gets echo's to the screen and ^] closes the
| console session. After the 'restore', 'xm console' echo's everything to
| the screen, and ^] doesn't do anything useful (apart from print ^] on
| the screen), like the console session hasn't connected to the serial
| port at all.
|
| Any idea's on that?
|
| Thanks
|
| James
|
| _______________________________________________
| Xen-devel mailing list
| Xen-devel@lists.xensource.com
| http://lists.xensource.com/xen-devel

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RE: differences in hvm save/restore in 3.1 vs 3.2

[James Harper]

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> There's a bug in the serial port emulation in qemu related to saving
and
> restoring. There's a patch floating around somewhere which fixes it,
but
> depending on what source tree you're using you may not have it yet.
One
> of the critical registers isn't saved and also isn't regenerated at
> restore time, meaning that serial port interrupts stop getting
delivered
> to the guest properly.
> 

That sounds like the sort of problem I'm seeing. It's obviously a
regression though as it was working in 3.1.

I'm using the Debian provided 3.2 packages but can easily apply a patch
if I can find it... I'll go searching tonight.

Thanks

James

Re: differences in hvm save/restore in 3.1 vs 3.2

[Brendan Cully]

On Friday, 04 July 2008 at 17:03, James Harper wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> > 
> > There's a bug in the serial port emulation in qemu related to saving
> and
> > restoring. There's a patch floating around somewhere which fixes it,
> but
> > depending on what source tree you're using you may not have it yet.
> One
> > of the critical registers isn't saved and also isn't regenerated at
> > restore time, meaning that serial port interrupts stop getting
> delivered
> > to the guest properly.
> > 
> 
> That sounds like the sort of problem I'm seeing. It's obviously a
> regression though as it was working in 3.1.
> 
> I'm using the Debian provided 3.2 packages but can easily apply a patch
> if I can find it... I'll go searching tonight.

It's probably this one:

http://xenbits.xensource.com/xen-unstable.hg/rev/13e10678e714

RE: differences in hvm save/restore in 3.1 vs 3.2

[James Harper]

> >
> > That sounds like the sort of problem I'm seeing. It's obviously a
> > regression though as it was working in 3.1.
> >
> > I'm using the Debian provided 3.2 packages but can easily apply a
patch
> > if I can find it... I'll go searching tonight.
> 
> It's probably this one:
> 
> http://xenbits.xensource.com/xen-unstable.hg/rev/13e10678e714
> 

I think that fixed it. Thanks.

James