Re: [Xen-devel] [PATCH][v2] Hybrid extension support in Xen

[Sheng Yang <sheng@xxxxxxxxxxxxxxx>]

On Tuesday 02 February 2010 21:19:32 Ian Campbell wrote:
> On Tue, 2010-02-02 at 12:54 +0000, Sheng Yang wrote:
> > On Tuesday 02 February 2010 19:22:21 Ian Campbell wrote:
> > > On Tue, 2010-02-02 at 08:16 +0000, Sheng Yang wrote:
> > > > +/* Reserve 128KB for grant table */
> > > > +#define GNTTAB_MEMBASE     0xfbfe0000
> > > > +#define GNTTAB_MEMSIZE     0x20000
> > >
> > > Why is this necessary? Isn't the grant table contained within one of
> > > the BARS on the virtual PCI device? What needs grant tables for prior
> > > to the kernel finding the PCI device which necessitates hardcoding
> > > these addresses in both guest and hypervisor?
> >
> > Thanks for so quick and detail comments. :)
> >
> > And this one is purposed, because we don't want to depends on QEmu. As
> > you see, we now have PV drivers, QEmu is an alternative way to provide
> > device model now. We think that still involving QEmu as a requirement is
> > somehow strange. So this reserved region is there, to drop the dependence
> > with QEmu to provide PV driver(PV driver depends on QEmu is still
> > strange, right?).
> 
> So with your patchset you can run an HVM guest with no qemu process at
> all? What about the other emulated devices which have no PV equivalent?
> How does the VM boot, does the BIOS have pv INT 13 handler?

No, not currently... Sorry for confusion. 

We just think QEmu provided the availability of PV driver seems unelegant, so 
we want to decouple them. Because what QEmu provided is a PCI IRQ and a MMIO 
region for grant table. And event channel is available without that PCI IRQ, 
so we think decouple MMIO from QEmu should be more elegant...

-- 
regards
Yang, Sheng

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