BAR and pci passthrough

[Neel Natu]

On Wed, Dec 2, 2015 at 3:13 AM, G. Amanakis via freebsd-virtualization
<freebsd-virtualization at freebsd.org> wrote:
> I am facing the following problem:
>     on a X9SCM with an E3-1220Lv2 I am trying to passthrough the onboard usb controllers. I disable the usb module from the kernel config and using pptdev the controllers are assigned to ppt devices. However running bhyve on FreeBSD 10.2 with:
>
>     sudo bhyve -AI -H -P -s 0:0,hostbridge -s 1:0,lpc -s 2:0,virtio-net,tap0 -s 3:0,virtio-blk,./linux.img -s 4:0,passthru,0/29/0 -l com1,stdio -c 2 -m 2048M linuxguest
>
> returns :
>
>     passthru device 0/29/0 BAR 0: base 0xdf823000 or size 0x400 not page aligned
>
> The problem probably that the length of the bar is smaller and not aligned with the pagesize. Could the length of the BAR be modified in order to perform the pci passthrough?

Yes, that's correct - the size of the BAR is not a multiple of the
page size which leads to the error. If this BAR is mapped into the
guest's address space then it will "leak" an additional 3K into the
guest (since the minimum nested mapping is 4KB in size).

It is hard to fix this in the general case if you want to truly
passthrough the BAR to the guest.

best
Neel

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