linux-kernel - Re: [PATCH v3 08/18] arm/arm64: KVM: Add PSCI version selection API

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Date:   Mon, 5 Feb 2018 11:50:31 +0100
From:   Christoffer Dall <christoffer.dall@...aro.org>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Andrew Jones <drjones@...hat.com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Peter Maydell <peter.maydell@...aro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Hanjun Guo <guohanjun@...wei.com>,
        Jayachandran C <jnair@...iumnetworks.com>,
        Jon Masters <jcm@...hat.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>
Subject: Re: [PATCH v3 08/18] arm/arm64: KVM: Add PSCI version selection API

On Mon, Feb 05, 2018 at 10:42:44AM +0000, Marc Zyngier wrote:
> On 05/02/18 09:58, Andrew Jones wrote:
> > On Mon, Feb 05, 2018 at 09:24:33AM +0000, Marc Zyngier wrote:
> >> On 04/02/18 12:37, Christoffer Dall wrote:
> 
> [...]
> 
> >>> Given the urgency of adding mitigation towards variant 2 which is the
> >>> driver for this work, I think we should drop the compat functionality in
> >>> this series and work this out later on if needed.  I think we can just
> >>> tweak the previous patch to enable PSCI 1.0 by default and drop this
> >>> patch for the current merge window.
> >>
> >> I'd be fine with that, as long as we have a clear agreement on the
> >> impact of such a move.
> > 
> > Yeah, that's what I was trying to figure out with my fancy tables. I might
> > be coming around more to your approach now, though. Ensuring the new->old
> > migration fails is a nice feature of this series. It would be good if
> > we could preserve that behavior without committing to a new userspace
> > interface, but I'm not sure how. Maybe I should just apologize for the
> > noise, and this patch be left as is...
> 
> How about we don't decide now?
> 
> I can remove this patch from the series so that the core stuff can make
> it into the arm64 tree ASAP (I think Catalin wants to queue something
> early this week so that it can hit Linus' tree before the end of the
> merge window), and then repost this single patch on its own (with fixes
> for the things that Christoffer found in his review) after -rc1.
> 
> It leaves us time to haggle over the userspace ABI (which is
> realistically not going to affect anyone), and we get the core stuff in
> place for SoC vendors to start updating their firmware.
> 
I agree, that's what I tried to suggest in my e-mail as well.  Just
remember to tweak the previous patch to actually enable PSCI 1.0 by
default.

Thanks,
-Christoffer