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

[Rodney W. Grimes]

> 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

Could you please factor out the white space changes and do that
seperately and sooner, it clouds the S/N in this review a bit.

> 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.

That makes more since to me.  Thanks.

> -- 
> John Baldwin
-- 
Rod Grimes                                                 rgrimes at freebsd.org