[vfio-users] hot-plug PCIe reassignment

[Alex Williamson]

On Fri, Jul 8, 2016 at 8:43 PM, Kajim Shanti <kajimshanti at gmail.com> wrote:

> Hi,
> Since I heard there are some PCIe devices that are hot-pluggable, I was
> wondering if it might work to cut off the power from a discrete graphic
> card in order to reassign it among different VMs without having to restart
> the host (and possibly the guests too?) Has anyone tried yet? Might it help
> to get a secondary PSU so that one could easily power on and off his
> descrete graphics without having to open the case? Thank you, sorry if the
> question was asked already.
>

Why would you need to cut power to the device to reassign it?  The
limitation here is guest drivers, the bus reset we do is already sufficient
for hot-plugging between guests, unless you've made the mistake of buying
AMD.  AFAIK, Windows already supports both hot unplug and re-plug, but
seems to require a guest reboot to really activate a hot-added GPU.  I
don't know if I've tested this on win10 though, maybe it's improved.
Anyway, a secondary PSU is probably only going to allow you to put the card
into a broken state where the GPU is still powered by the slot, but doesn't
have the additional external power.  Seems like a non-zero chance of
letting out the magic smoke doing something like that too.
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