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

From: Mark Cave-Ayland
Subject: Re: [Qemu-devel] Incorrect memory region address with large 64-bit PCI BARs
Date: Sun, 12 Mar 2017 11:16:44 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Icedove/45.6.0

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.



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