Re: [Xen-devel] QEMU e820 Reservation (FW_CFG_E820_TABLE and fw_cfg etc/e820)

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2015-03-04 at 10:38 +0000, Gordan Bobic wrote:
> > I don't follow you here: what is the etc/e820 interface?
> 
> See the 2nd patch I mentioned above, which supposedly
> adds "etc/e820 fw_cfg file" (whatever that means).

The problem here is that hvmloader controls and can make modifications
to the memory map, and therefore needs to be the entity which provides
the e820 to SeaBIOS. etc/e820 comes from qemu which does not have full
information.

I suppose we could enable etc/e820 for those who really know what they
are doing, but it seems like it would be open to abuse (and resulting
bug reports to us).

Xen already has XENMEM_set_memory_map and XENMEM_memory_map which the
tools can use to pass a memory map to the guest (e.g. where hvmloader
could retrieve it as a baseline).

I think today this is only really used with pv guests using e820_host=1
option. Perhaps that could be extended to HVM guests? Or Perhaps a
separate (xenstore based?) mechanism for the toolstack to blacklist
memory regions in the guest so hvmloader can take those into account?

Ian.


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