Re: [Xen-devel] [PATCH v2] xen/hvmloader: define a TOM register

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 25 Feb 2013, Keir Fraser wrote:
> On 25/02/2013 06:50, "Xudong Hao" <xudong.hao@xxxxxxxxx> wrote:
> 
> > v2:
> > * Define TOM register as one byte
> > 
> > Define a TOM(top of memory) register to report the base of PCI memory, so 
> > that
> > qemu should update MMIO by reading this register value. TOM register are
> > defined
> > to one byte in PCI configure space, because that only upper 4 bit of PCI
> > memory
> > takes effect.
> > 
> > With the combination of qemu upstream, this should be a fix for PCI MMIO 
> > hole
> > configuration. Upstream qemu set 0xe0000000 as TOM, but guest bios may set
> > MMIO
> > to 0x80000000~0xe0000000.
> 
> Why does qemu (when used as the Xen device model) care about the location of
> the PCI hole start?

QEMU needs to know where the end of the guest's RAM is (because there is
where it allocates the videoram and other stuff), so at least the size
of the MMIO hole is important.
Also, given that Xen support is tightly integrated in QEMU now, and QEMU
assumes it knows everything about RAM and MMIO regions, it is probably a
good idea to give it these information anyway.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel