Issues with GTX960 on CentOS7 using bhyve PCI passthru (FreeBSD 11-RC2)

soralx at soralx at
Thu Jan 12 05:39:42 UTC 2017

>   That's a different issue - it's unlikely, if not impossible, to 
> configure bhyve with enough RAM to hit 37 bits worth where that would 
> become a problem. No need to worry about that.

Well, there may be peripheral cards that have less bits... Anyway, I
see what you mean: memory manager can always remap the DMA regions
to lower virtual addresses. Good to know it's not an issue.

>   There are lots of BIOS/UEFI implementations out there that have the 
> same restriction. In general, there should be no need for a guest to 
> reprogram device BARs.

There are all sorts of situations... But anyway, if it is too much
work, then we can forget about this until someone needs it again.

>   After changing the 64-bit BAR base address, did you still need the 
> pci=nocrs option for Linux ? I'd hope this would be no longer necessary.

No. As expected, the option is no longer needed.

BTW, is it [generally] safe to decrease the BAR base address further?
My workstation has a CPU with just 36 address bits...

>   The problem is the knowledge set of graphics/GPU knowhow and
> equipment access, and bhyve/PCI programming, are disjoint. The time
> I've spent on it has been the inverse, where I feel that I've spent a
> half-day doing things that anyone who knew about graphics could get
> done in a half-hour :)
>   For these type of issues, joint work is best to leverage the
> knowledge of both sides. From my point-of-view, the work you've done
> has been very helpful.

Yeah, we could benefit from more information exchange, I agree. I am
trying to do my part to share what I learned; I started with no
knowledge of bhyve, PCI, or GPU passthrough a week ago -- so for now
my efforts appear useful, but soon the progress will stop, and we
will need someone with real knowledge to step in.

Incidentally, could someone put a note about that hardcoded BAR base
on the bhyve PCI passthrough page [0] if it won't be fixed soon, so
many others can play with VGA passthrough meanwhile?


> later,
> Peter.

[SorAlx]  ridin' VN2000 Classic LT

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