Re: [PATCH] xen/pvhvm: If xen_platform_pci=0 is set don't blow up.

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

On Wed, 4 Dec 2013, Ian Campbell wrote:
> On Wed, 2013-12-04 at 10:51 +0000, Stefano Stabellini wrote:
> > On Wed, 4 Dec 2013, Ian Campbell wrote:
> > > > +bool xen_has_pv_devices(void)
> > > > +{
> > > > +	if (!xen_domain())
> > > > +		return false;
> > > > +
> > > > +	if (xen_hvm_domain()) {
> > > > +		/* User requested no unplug, so no PV drivers. */
> > > > +		if (xen_emul_unplug & XEN_UNPLUG_NEVER)
> > > > +			return false;
> > > 
> > > I think you need
> > > 		if (xen_emul_unpug & XEN_UNPLUG_UNNECESSARY)
> > > 			return true;
> > > don't you?
> > 
> > XEN_UNPLUG_UNNECESSARY was introduced to enable the platform PCI device
> > even if it didn't respond properly to the unplug protocol.
> > The corresponding parameter is called "unnecessary" because if you pass
> > it to the kernel you mean that it is unnecessary to unplug the emulated
> > devices but you can use the pv devices anyway.
> > 
> > So no, we shouldn't check for XEN_UNPLUG_UNNECESSARY here.
> 
> Oh, we will eventually fall through to the return true, so it does
> actually work out OK.
> 
> I'd still be in favour of handling each option explicitly, for clarity.
> Which means checking for XEN_UNPLUG_UNNECESSARY.

I think is wrong to check for any xen_emul_unpug options in this function.
The xen_emul_unpug options should be used to set the right value of
xen_platform_pci_unplug. (See my other reply.)


> > > > +		/* And user has xen_platform_pci=0 set in guest config as
> > > > +		 * driver did not modify the value. */
> > > > +		if (!xen_platform_pci_unplug)
> > > > +			return false;
> 
> I assume this check doesn't trigger if unnecessary has been specified?
 
right