Re: [Qemu-devel] Incorrect memory region address with large 64-bit PCI BARs

[Mark Cave-Ayland]

On 12/03/17 03:56, Michael S. Tsirkin wrote:

> After looking at it some more, I think the issue is merely with how info
> mtree presents information, which confuses instead of helping when
> overlap triggers. Specifically
>     000001ff00000000-000001ffffffffff (prio 0, i/o): pci-mmio
>       ...
>       000001fe04040000-000001fe04043fff (prio 1, i/o): virtio-pci
> 
> really means that virtio-pci is not visible at all, this
> happens because it starts at offset ffffffff04040000 which is
> outside the parent.
> 
> I think that the cleanest fix is probably to show 128 bit addresses,
> then user will see the real addresses:
> 
>     000001ff00000000-000001ffffffffff (prio 0, i/o): pci-mmio
>       ...
>       1000001fe04040000-1000001fe04043fff (prio 1, i/o): virtio-pci
>       
> and now it's clear what is going on: virtio-pci is outside pci-mmio.
> 
> This would have pointed Mark in the right direction earlier.
> 
> Thoughts? Patch?

Presumably if someone tried to do this on real hardware, the BAR address
would lie outside of the pci-mmio region and effectively isn't mapped?

If this is the case I'd be happy with a simple qemu_log() showing the
full 64-bit address and region name explaining that it couldn't be
mapped underneath its parent because it was outside its parent region,
and skip the mapping.


ATB,

Mark.