Re: [Xen-devel] [PATCH QEMU-XEN] xen/pt: Start with emulated PCI_COMMAND set to zero.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 11 Jun 2015, Jan Beulich wrote:
> >>> On 10.06.15 at 22:53, <konrad@xxxxxxxxxx> wrote:
> > --- a/hw/xen/xen_pt.c
> > +++ b/hw/xen/xen_pt.c
> > @@ -785,7 +785,9 @@ out:
> >          xen_host_pci_set_word(&s->real_device, PCI_COMMAND,
> >                                pci_get_word(d->config + PCI_COMMAND) | cmd);
> >      }
> > -
> > +    /* Until the guest enables the device use d->config values which will
> > +     * inhibit pci_bar_address & pci_update_mappings from triggering 
> > updates.*/
> > +    pci_set_word(d->config + PCI_COMMAND, 0);
> >      memory_listener_register(&s->memory_listener, &address_space_memory);
> >      memory_listener_register(&s->io_listener, &address_space_io);
> >      XEN_PT_LOG(d,
> 
> Well, I can see this as something to be tried out as an experiment,
> but it looks like you mean this to be a proper submission for
> inclusion upstream? Or maybe not, considering that qemu-devel
> wasn't even Cc-ed? In any case - what we need here is a general
> solution to at least the initialization part of the problem, i.e. all
> fields we emulate some or all bits for need to have d->config[]
> updated accordingly (i.e. you need to merge d->config[] and
> XenPTReg's data field based on the respective XenPTRegInfo's
> emu_mask, but perhaps simply copying the data field to
> d->config[] would have the same effect; if it doesn't, we have
> yet another problem). For the command register this for example
> means that it is in no way guaranteed that it would end up being
> zero; its emu_mask however guarantees that the memory and I/O
> decode bits would start out as zero (which is what you're after).

I am not sure I can ask Konrad to come up with a larger general solution
when his intent was just to fix this issue.  This one liner is OK for
that.

Of course it would be great if Konrad wanted to volunteer to submit a
patch that updates d->config for all fields, or gets rid of reg->data
entirely.

Konrad, what do you think?

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