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

On 1/23/19 11:30 AM, Paul Mackerras wrote:

On Wed, Jan 23, 2019 at 05:45:24PM +1100, Benjamin Herrenschmidt wrote:

quoted

On Tue, 2019-01-22 at 16:26 +1100, Paul Mackerras wrote:

quoted

On Mon, Jan 07, 2019 at 08:10:05PM +0100, Cédric Le Goater wrote:

quoted

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.