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 11:23 PM, Konrad Rzeszutek Wilk wrote:
> Gordan Bobic <gordan@xxxxxxxxxx> 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.
> Right.  The code just prints the E820 that was constructed b/c of the e820_host 
> =1 parameter as the first output.  Then the second one is what was constructed 
> originally.
>
> The code that would tie in the E820 from the hyper call and the alter how the 
> hvmloader sets it up is not yet done.
>
>
> > 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.
> Right.  That is correct since the patch I sent just outputs stuff.  No real 
> changes to the E820 yet.
/me *facepalms*

That indeed explains everything. :)

But having had a thorough look through the memory mappings (see my other 
long, rambling email), I don't actually see an obvious area where RAM 
might overwrite a dom0 IOMEM range - assuming the "HOLE" part isn't 
mapped as RAM in domU.
Or to summarize:
dom0 PCI IOMEM actually has mappings from a8000000 onward, and giving 
domU up to that much memory works fine. So the memory stomp must be 
happening from a8000000 onward. But - the only things above that address 
in domU are the HOLE up to fc000000 and RESERVED up to ffffffff. So no 
domU memory is getting mapped into the IOMEM range anyway - which begs 
the question of what is _actually_ causing the crash. Stuff I haven't 
yet found in domU getting mapped into the a7800000-fc000000 hole 
overlapping dom0 IOMEM? SeaBIOS doing smething odd in the 
fc000000-fec8b000 range marked RESERVED in domU?
Or am I reading this all wrong?

Gordan

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