From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paul Mackerras <paulus@ozlabs.org>
Subject: Re: [PATCH 18/19] KVM: PPC: Book3S HV: add passthrough support
Date: Wed, 23 Jan 2019 21:30:09 +1100
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Cc: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
 =?iso-8859-1?Q?C=E9dric?= Le Goater <clg@kaod.org>,
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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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.

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/.

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...

Paul.