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

[Gordan Bobic <gordan@xxxxxxxxxx>]

Hi,

I've been looking into custom e820 maps for domUs again, and
found that functionality to provide QEMU with hints regarding
e820 mapping has been upstream since some time in
2010 (FW_CFG_E820_TABLE) with more finely grained control
(usable rather than just reserved entries) upstream since
2013 (fw_cfg etc/e820).

The respective patches are here:
http://lists.gnu.org/archive/html/qemu-devel/2010-02/msg00996.html
http://lists.gnu.org/archive/html/qemu-devel/2013-11/msg00593.html

What I have not been able to find is any documentation at
all on how this e820 data can be given to QEMU when starting
a domain. I can see from the structs in the patches how the
data is packed for the relevant code to consume, but I cannot
figure out what is the delivery vector for this data. How
can I get QEMU to ingest the hints about any additional
reserved e820 blocks?

For context, I need this to work around IOMMU implementation
bugs and mark areas of address space as reserved so that
the guest doesn't trample over the host's PCI I/O ranges
(which IOMMU should intercept, but being buggy, it doesn't).

Many thanks in advance.

Gordan

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