Windows 10 guests fail to boot when attempting to passthrough network card

[John Baldwin]

On 5/19/19 6:24 AM, Rodney W. Grimes wrote:
>> Does the card have multiple BARs? Can you send us the output of pciconf -lvb for the card?
>>
>> There is a bug in bhyve where if the OS assigns the 0xffffffff sentinel to more than one BAR simultaneously it is not compatible with bhyve?s memory model for the guest.
> 
> The "we talked" below is myself and Nick talking about exactly that
> which came from jhb@ pointing out to me in a hall wall
> conversation here at BSDCan that this is the cause of this
> problem and is a known issue.
> 
> Does anyone have fixes for this issue?

I have not tested this at all, but I have a candidate patch to fix the root
issue at https://github.com/freebsd/freebsd/compare/master...bsdjhb:bhyve_passthrough_barsize

My first guess at the problem wasn't quite right (though Windows does indeed size
BARs in parallel).  For pass-through devices we aren't currently correctly disabling
access to a BAR when the guest disables it in the PCI command register which in
turn trips the assertion when using a Windows guest, but in general we need to be
honoring the enable bits when set or cleared by the guest.

-- 
John Baldwin