Re: [Xen-devel] PVHVM drivers in upstream linux kernel

[Juergen Gross <jgross@xxxxxxxx>]

On 12/02/2014 12:36 PM, Ian Campbell wrote:
> On Tue, 2014-12-02 at 12:33 +0100, Juergen Gross wrote:
> > On 12/02/2014 12:05 PM, Ian Campbell wrote:
> > > On Tue, 2014-12-02 at 10:54 +0000, David Vrabel wrote:
> > > > On 02/12/14 09:39, Juergen Gross wrote:
> > > > > Hi,
> > > > >
> > > > > looking into the upstream linux sources I realized that the PVHVM
> > > > > drivers of XEN are only available with the pvops kernel. Is this on
> > > > > purpose? Shouldn't the frontend drivers, xen/platform-pci.c etc. be
> > > > > configurable without having to enable CONFIG_PARAVIRT?
> > > > I suppose that would be possible but I don't think it's a useful
> > > > configuration because you would lose PV spinlocks for example.
> > > IIRC the reason this hasn't been implemented until now is that
> > > refactoring would be required to the various bits of driver code which
> > > assumes PAE + PARAVIRT when they aren't strictly needed, e.g. grant
> > > table code. Whether its worth the churn at this stage is debatable, but
> > > I think the (in)ability to use PV spinlocks is a red-herring.
> > >
> > > Adding PV drivers to an HVM guest is a useful thing to do, even without
> > > PV spinlocks. PV IO gets you far more incremental benefit than the locks
> > > do, adding PV IO paths is the number 1 thing which should be done to any
> > > guest.
> > I take this as an "ack" to change this. :-)
> It's a best "IMHO being able to do this is a useful thing". I can't ack
> the actual final patch, a) I'm not a relevant maintainer and b) I've not
> seen the patch.
It was not meant to be taken as an ack for a not yet written patch. :-)

> > Okay, how do the current config settings regarding Xen look like?
> ...I'll leave the mechanics down to you and the maintainers to thrash
> out.
Yeah, stay tuned. :-)


Juergen

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