Re: [Qemu-devel] [Qemu-ppc] KVM-PR is broken with current QEMU

[Thomas Huth <thuth@redhat.com>]

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On Thu, 22 Sep 2016 11:57:15 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Wed, Sep 21, 2016 at 10:22:11AM +0200, Thomas Huth wrote:
> > On 20.09.2016 16:39, Cédric Le Goater wrote:
> > > On 09/20/2016 04:24 PM, Thomas Huth wrote:
> > >> On 20.09.2016 16:04, Cédric Le Goater wrote:
> > [...]
> > >>> There are other issues after in the guest (kernel crashing). But I think
> > >>> these are related to TM which is not supported in KVM-PR. I am not sure
> > >>> where we are on that point.
> > >>
> > >> There was a patch some months ago:
> > >>
> > >> https://lists.gnu.org/archive/html/qemu-ppc/2016-04/msg00046.html
> > >>
> > >> ... but I think it has never been included, as far as I can see.
> > > 
> > > and with that patch, the guest fully boots. But David had some concerns
> > > on the way it is done. It would be nice to put some cycle on this. 
> > 
> > Looking at the mail thread, I think TM should be currently disabled for
> > both, KVM-PR and TCG, i.e. only enabled for KVM-HV. The TM support in
> > TCG is just fake, since TBEGIN always fails.
> 
> Right.  So there's two questions here
> 
> 1) Is qemu correctly advertising availability of TM in the device
> tree?

If I've got that right, it's currently always advertising TM, even if
it's not really available (in TCG mode and PR mode).

> If not we need to fix that, which might involve adding a kernel
> capability for the PR case.
> 
> 2) Is the kvm unit test properly checking for availability of TM
> before executing?

Not yet. That's why it would be good to get a proper way for testing
for the availability of TM --> i.e. something like Anton's patch.

> > Once we've got proper TM support in TCG, this can be easily changed
> > within QEMU. And once we've got TM support in KVM-PR, I think we should
> > also introduce a capability flag to KVM which can be used to inform QEMU
> > about this.
> > 
> > So I think Anton's patch currently just lacks the check for TCG.
> > Anton, if you've got some spare minutes, could you maybe send an updated
> > version of that patch?
> 
> Sorry, which patch of Anton's?

This one:
https://lists.gnu.org/archive/html/qemu-ppc/2016-04/msg00415.html

 Thomas

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