[PATCH 18/19] KVM: PPC: Book3S HV: add passthrough support

[Cédric Le Goater]

On 1/23/19 11:30 AM, Paul Mackerras wrote:
> On Wed, Jan 23, 2019 at 05:45:24PM +1100, Benjamin Herrenschmidt wrote:
>> On Tue, 2019-01-22 at 16:26 +1100, Paul Mackerras wrote:
>>> On Mon, Jan 07, 2019 at 08:10:05PM +0100, Cédric Le Goater wrote:
>>>> Clear the ESB pages from the VMA of the IRQ being pass through to the
>>>> guest and let the fault handler repopulate the VMA when the ESB pages
>>>> are accessed for an EOI or for a trigger.
>>>
>>> Why do we want to do this?
>>>
>>> I don't see any possible advantage to removing the PTEs from the
>>> userspace mapping.  You'll need to explain further.
>>
>> Afaik bcs we change the mapping to point to the real HW irq ESB page
>> instead of the "IPI" that was there at VM init time.

yes exactly. You need to clean up the pages each time.
 
> So that makes it sound like there is a whole lot going on that hasn't
> even been hinted at in the patch descriptions...  It sounds like we
> need a good description of how all this works and fits together
> somewhere under Documentation/.

OK. I have started doing so for the models merged in QEMU but not yet 
for KVM. I will work on it.

> In any case we need much more informative patch descriptions.  I
> realize that it's all currently in Cedric's head, but I bet that in
> two or three years' time when we come to try to debug something, it
> won't be in anyone's head...

I agree. 


So, storing the ESB VMA under the KVM device is not shocking anyone ?  

Thanks,

C.