linux-kernel - Re: [PATCH 3/8] arm64: cpufeature: Add CPU capability for AArch32 EL1 support

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Date:   Wed, 15 Apr 2020 18:00:29 +0100
From:   Will Deacon <will@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mark Rutland <mark.rutland@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Doug Anderson <dianders@...omium.org>, kernel-team@...roid.com
Subject: Re: [PATCH 3/8] arm64: cpufeature: Add CPU capability for AArch32
 EL1 support

Hi Marc,

On Wed, Apr 15, 2020 at 09:55:57AM +0100, Marc Zyngier wrote:
> On 2020-04-14 22:31, Will Deacon wrote:
> > Although we emit a "SANITY CHECK" warning and taint the kernel if we
> > detect a CPU mismatch for AArch32 support at EL1, we still online the
> > CPU with disastrous consequences for any running 32-bit VMs.
> > 
> > Introduce a capability for AArch32 support at EL1 so that late onlining
> > of incompatible CPUs is forbidden.
> > 
> > Signed-off-by: Will Deacon <will@...nel.org>
> 
> Definitely an improvement over the current situation, as the direct read
> of ID_AA64PFR0 was always a bit dodgy. Given that I'm pretty sure these new
> braindead SoCs are going to run an older version of the kernel, should we
> Cc stable for this?

I don't think there's a real need for -stable given that we do at least
taint the kernel. That's likely to annoy vendors enough to backport this
themselves ;)

Will