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[Xen-devel] xen pci and vga passthrough + option roms



Hi Konrad,

I'm starting a new thread .. since i'm essentially trying to start over from 
scratch.
(shoot i forgot to include xen-devel on the first mail ...)

- Xen-unstable the latest and greatest
- Linux 3.13-rc7 as dom0 and guest kernel
- Qemu-xen
- Some patches (vga="none", enableing qemu debug, fixing builderrors when 
enabling qemu debug)

I'm now first trying to replicate you :-) (don't worry .. it won't hurt :p),
i'm using an intel NIC now (found one laying around and it has a rom.
and after it was flashed .. it even has valid rom content :-) )

Now the first experiment is to see if the sequence "echo 1 > rom; cat rom > 
romfile.bin; echo 0 > rom;" works.

- Running Xen, on dom0, NIC owned by e1000e: dumping the rom works
- Running Xen, on dom0, NIC owned by pciback: dumping the rom FAILS, kernel 
gives "cat: rom: Input/output error"
- Running Xen, in a HVM guest, NIC passedthrough: dumping the rom works, 
contents are the same as under dom0

The failure with pciback is perhaps because the device wasn't initialized on 
boot because it was seized by pciback.
So generally speaking the rombar of pci devices is correctly passed through and 
can be dumped.

So it indeed appears to be a VGA passthrough specific issue.

This was on my intel machine, but unfortunately that one has an IGD that shares 
it's pci-e lanes with the only pcie x16 slot,
so will put the NIC in my AMD machine .. and verify if it works there and then 
continue with the VGA card.

Now trying on the AMD machine:

NIC:
- Running Xen, on dom0, NIC owned by e1000e: dumping the rom works
- Running Xen, on dom0, NIC owned by pciback: dumping the rom FAILS, kernel 
gives "cat: rom: Input/output error"
- Running Xen, in a HVM guest, NIC passedthrough: dumping the rom works, 
contents are the same as under dom0

VGA card:
- Running Xen, on dom0, VGA card owned by radeon: dumping the rom works
- Running Xen, on dom0, VGA card owned by nothing (due to setting nomodeset): 
dumping the rom FAILS, kernel gives "cat: rom: Input/output error"
- Running Xen, on dom0, VGA card owned by pciback: dumping the rom FAILS, 
kernel gives "cat: rom: Input/output error"
- Running Xen, in a HVM guest, VGA card passedthrough: dumping the rom works, 
contents are DIFFERENT from dom0, i get the BOCHS VGAbios

Prelimanary conclusions:
- Passing through the rombar from a NIC works
- Passing through the rombar from a VGA card doesn't work out of the box.
- the sequence "echo 1 > rom; cat rom > romfile.bin; echo 0 > rom;" works but 
seems to rely on a loaded and working driver and is thus not very reliable for 
testing
  so i need to dust of my arithmatic and use /dev/kmem and dd.
- So Anthony is probably right .. something is playing tricks with the rombar 
when it's VGA class, even if it's the secondary card in the Guest.

--
Sander


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