[Xen-devel] Re: [RFC Patch] Support for making an E820 PCI hole in toolstack (xl + xm)

[Gianni Tedesco <gianni.tedesco@xxxxxxxxxx>]

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?

Gianni


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