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

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Message-ID: <7eb71dd4-c06b-9680-0280-03569925283b@arm.com>
Date:   Mon, 5 Feb 2018 10:42:44 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Andrew Jones <drjones@...hat.com>
Cc:     Christoffer Dall <christoffer.dall@...aro.org>,
        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 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.

Thoughts?

	M.
-- 
Jazz is not dead. It just smells funny...