[PATCH 1/6] KVM: PPC: Book3S HV: XIVE: initialize private pointer when VPs are allocated

[Greg Kurz]

On Tue, 24 Sep 2019 15:28:55 +1000
Paul Mackerras <paulus at ozlabs.org> wrote:

> On Mon, Sep 23, 2019 at 05:43:37PM +0200, Greg Kurz wrote:
> > From: Cédric Le Goater <clg at kaod.org>
> > 
> > Do not assign the device private pointer before making sure the XIVE
> > VPs are allocated in OPAL and test pointer validity when releasing
> > the device.
> > 
> > Fixes: 5422e95103cf ("KVM: PPC: Book3S HV: XIVE: Replace the 'destroy' method by a 'release' method")
> > Signed-off-by: Cédric Le Goater <clg at kaod.org>
> > Signed-off-by: Greg Kurz <groug at kaod.org>
> 
> What happens in the case where the OPAL allocation fails?  Does the
> host crash, or hang, or leak resources?  I presume that users can
> trigger the allocation failure just by starting a suitably large
> number of guests - is that right?  Is there an easier way?  I'm trying
> to work out whether this is urgently needed in 5.4 and the stable
> trees or not.
> 

Wait... I don't quite remember how this patch landed in my tree but when
I look at it again I have the impression it tries to fix something that
cannot happen.

It is indeed easy to trigger the allocation failure, eg. start more than
127 guests on a Witherspoon system. But if this happens, the create
function returns an error and the device isn't created. I don't see how
the release function could hence get called with a "partially initialized"
device.

Please ignore this patch. Unfortunately the rest of the series doesn't
apply cleanly without it... I'll rebase and post a v2.

Sorry for the noise :-\

> Paul.