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

[Sheng Yang <sheng@linux.intel.com>]

On Tuesday 02 February 2010 21:35:23 Keir Fraser wrote:
> On 02/02/2010 11:22, "Ian Campbell" <Ian.Campbell@eu.citrix.com> 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?
> 
> I didn't even find where these get used, except to reserve an area in e820,
> and it wasn't clear why that reservation is necessary.
> 
It has been used in the last [6/6] patch of Linux kernel side, which would use 
the pages to map grant table. It works the same as the MMIO region in PVonHVM 
device. Reserve it in BIOS because we think it's more elegant than depends on 
QEmu to provide the reserved memory space.

-- 
regards
Yang, Sheng