Re: [Xen-devel] HVM support for e820_host (Was: Bug: Limitation of <=2GB RAM in domU persists with 4.3.0)

[Gordan Bobic <gordan@xxxxxxxxxx>]

On 09/05/2013 10:13 PM, Gordan Bobic wrote:
> Right, finally got around to trying this with the latest patch.
>
> With e820_host=0 things work as before:
>
> (XEN) HVM3: BIOS map:
> (XEN) HVM3:  f0000-fffff: Main BIOS
> (XEN) HVM3: E820 table:
> (XEN) HVM3:  [00]: 00000000:00000000 - 00000000:0009e000: RAM
> (XEN) HVM3:  [01]: 00000000:0009e000 - 00000000:000a0000: RESERVED
> (XEN) HVM3:  HOLE: 00000000:000a0000 - 00000000:000e0000
> (XEN) HVM3:  [02]: 00000000:000e0000 - 00000000:00100000: RESERVED
> (XEN) HVM3:  [03]: 00000000:00100000 - 00000000:e0000000: RAM
> (XEN) HVM3:  HOLE: 00000000:e0000000 - 00000000:fc000000
> (XEN) HVM3:  [04]: 00000000:fc000000 - 00000001:00000000: RESERVED
> (XEN) HVM3:  [05]: 00000001:00000000 - 00000002:1f800000: RAM
>
>
> I seem to be getting two different E820 table dumps with e820_host=1:
>
> (XEN) HVM1: BIOS map:
> (XEN) HVM1:  f0000-fffff: Main BIOS
> (XEN) HVM1: build_e820_table:91 got 8 op.nr_entries
> (XEN) HVM1: E820 table:
> (XEN) HVM1:  [00]: 00000000:00000000 - 00000000:3f790000: RAM
> (XEN) HVM1:  [01]: 00000000:3f790000 - 00000000:3f79e000: ACPI
> (XEN) HVM1:  [02]: 00000000:3f79e000 - 00000000:3f7d0000: NVS
> (XEN) HVM1:  [03]: 00000000:3f7d0000 - 00000000:3f7e0000: RESERVED
> (XEN) HVM1:  HOLE: 00000000:3f7e0000 - 00000000:3f7e7000
> (XEN) HVM1:  [04]: 00000000:3f7e7000 - 00000000:40000000: RESERVED
> (XEN) HVM1:  HOLE: 00000000:40000000 - 00000000:fee00000
> (XEN) HVM1:  [05]: 00000000:fee00000 - 00000000:fee01000: RESERVED
> (XEN) HVM1:  HOLE: 00000000:fee01000 - 00000000:ffc00000
> (XEN) HVM1:  [06]: 00000000:ffc00000 - 00000001:00000000: RESERVED
> (XEN) HVM1:  [07]: 00000001:00000000 - 00000001:68870000: RAM
> (XEN) HVM1: E820 table:
> (XEN) HVM1:  [00]: 00000000:00000000 - 00000000:0009e000: RAM
> (XEN) HVM1:  [01]: 00000000:0009e000 - 00000000:000a0000: RESERVED
> (XEN) HVM1:  HOLE: 00000000:000a0000 - 00000000:000e0000
> (XEN) HVM1:  [02]: 00000000:000e0000 - 00000000:00100000: RESERVED
> (XEN) HVM1:  [03]: 00000000:00100000 - 00000000:a7800000: RAM
> (XEN) HVM1:  HOLE: 00000000:a7800000 - 00000000:fc000000
> (XEN) HVM1:  [04]: 00000000:fc000000 - 00000001:00000000: RESERVED
> (XEN) HVM1: Invoking ROMBIOS ...
>
> I cannot quite figure out what is going on here - these tables can't
> both be true.
>
> Looking at the IOMEM on the host, the IOMEM begins at 0xa8000000 and
> goes more or less contiguously up to 0xfec8b000.
>
> Looking at dmesg on domU, the e820 map more or less matches the second
> dump above.
>
> So I guess that should work - the entire IOMEM area of the host is in
> fact not mapped. But since I've passed 8GB of RAM to domU, shouldn't
> there be another usable RAM area after 00000001:00000000 ?
I should probably also mention that the domU does in fact see 8GB of 
RAM, so clearly it is working.
The PCI IOMEM reservations on the host are:
# lspci -vvv | grep Region | grep Memory | sed -e 's/.*Memory at //' | sort
a8000000 (64-bit, prefetchable) [disabled] [size=128M]
b0000000 (64-bit, prefetchable) [disabled] [size=64M]
b4000000 (64-bit, prefetchable) [size=64M]
b8000000 (64-bit, prefetchable) [size=128M]
c0000000 (64-bit, prefetchable) [size=256M]
d7efc000 (32-bit, non-prefetchable) [size=16K]
d8000000 (64-bit, non-prefetchable) [size=64K]
dc000000 (64-bit, non-prefetchable) [size=16K]
f3df4000 (64-bit, non-prefetchable) [size=16K]
f3df8000 (32-bit, non-prefetchable) [size=1K]
f3dfa000 (32-bit, non-prefetchable) [size=1K]
f3dfc000 (32-bit, non-prefetchable) [size=2K]
f3dfe000 (64-bit, non-prefetchable) [size=256]
f3edc000 (64-bit, non-prefetchable) [size=16K]
f3fdc000 (64-bit, non-prefetchable) [size=16K]
f4000000 (32-bit, non-prefetchable) [disabled] [size=32M]
f7ffc000 (32-bit, non-prefetchable) [disabled] [size=16K]
f8000000 (32-bit, non-prefetchable) [size=32M]
fbcfc000 (32-bit, non-prefetchable) [size=16K]
fbdfe000 (64-bit, non-prefetchable) [disabled] [size=8K]
fbeef000 (32-bit, non-prefetchable) [size=2K]
fbeefc00 (32-bit, non-prefetchable) [size=16]
fec8a000 (32-bit, non-prefetchable) [size=4K]


What is a little concerning is that my GPU in dom0 has it's IOMEM mapped at
E0000000-E7FFFFFF
E8000000-EBFFFFFF
EC000000-EDFFFFFF

Granted, this fits into a convenient hole in the host map
0xdc004000-0xf3df4000 but I cannot see that hole being listed as such in 
the xl dmesg E820 table dump. Is this _really_ working, or is it working 
by pure luck?
Gordan

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