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xen-devel
Re: [Xen-devel] Re: [RFC Patch] Support for making an E820 PCI hole in t
On Wed, 2010-11-17 at 11:43 +0000, Ian Campbell wrote:
> On Wed, 2010-11-17 at 11:14 +0000, Gianni Tedesco wrote:
> > On Fri, 2010-11-12 at 23:08 +0000, Konrad Rzeszutek Wilk wrote:
> > > Hey guys,
> > >
> > > Attached is an RFC patch for making a PCI hole in the PV guests. This
> > > allows
> > > PV guests(*) with 4GB or more to now properly work with or without
> > > PCI passthrough cards.
> > >
> > > Previously the Linux kernel would not be able to allocate the PCI region
> > > underneath the 4GB region as that region was all System RAM. And you
> > > would see
> > > this:
> > >
> > > [ 0.000000] PM: Registered nosave memory: 00000000000a0000 -
> > > 0000000000100000
> > > [ 0.000000] PCI: Warning: Cannot find a gap in the 32bit address range
> > > [ 0.000000] PCI: Unassigned devices with 32bit resource registers may
> > > break!
> > > [ 0.000000] Allocating PCI resources starting at 100100000 (gap:
> > > 100100000:400000)
> > >
> > >
> > > This patchset punches an PCI hole in the E820 region and as well fills
> > > the P2M properly,
> > > so that now you can see (*):
> > > [ 0.000000] Allocating PCI resources starting at a0000000 (gap:
> > > a0000000:60000000)
> > >
> > > It adds a new option to guest config file, which is "pci_hole". The user
> > > can
> > > specify the PFN number, such as '0xc0000' or in case of using the xl, '1'
> > > which
> > > will automatically figure out the start of the PCI address.
> > >
> > > *: This option requires support in the Linux kernel to actually deal with
> > > two
> > > entries in the E820 map and P2M space filled with ~0.
> >
> > Doesn't this problem affect dom0 also? How is it to be fixed there?
>
> Domain 0 sees the actual host e820 map instead of the paravirtualised
> one constructed by the tools for domU. So the BIOS effectively takes the
> place of the tools side of this patch for dom0.
Hmm, of course, I did think xen "sanitised" it somehow though.
I suppose I just assumed (hoped) this may fix my dom0 boot crash issues.
Gianni
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