Re: PVHVM drivers in upstream linux kernel

[Ian Campbell <Ian.Campbell@citrix.com>]

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.

> 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.

Ian.