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

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Date:   Fri, 17 Apr 2020 10:44:16 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     maz@...nel.org
Cc:     will@...nel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        mark.rutland@....com, anshuman.khandual@....com,
        catalin.marinas@....com, saiprakash.ranjan@...eaurora.org,
        dianders@...omium.org, kernel-team@...roid.com
Subject: Re: [PATCH 3/8] arm64: cpufeature: Add CPU capability for AArch32 EL1
 support

On 04/15/2020 02:22 PM, Marc Zyngier wrote:
> On Wed, 15 Apr 2020 14:15:51 +0100
> Suzuki K Poulose <suzuki.poulose@....com> wrote:
> 
>> On 04/15/2020 11:14 AM, Will Deacon wrote:
>>> On Wed, Apr 15, 2020 at 11:13:54AM +0100, Suzuki K Poulose wrote:
>>>> On 04/14/2020 10:31 PM, 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>
>>>>
>>>> One of the other important missing sanity check for KVM is the VMID width
>>>> check. I will code something up.
>>>
>>> Cheers! Do we handle things like the IPA size already?
>>
>> Good point. No, we don't. I will include this too.
> 
> There is also the question of the ARMv8.5-GTG extension. I have a patch
> that treats it as non-strict, but that approach would fail with KVM if
> we online a late CPU without support for the right page size at S2.

Good point. Again this can be added to the list of checks performed on
the hot-plugged CPUs along with IPA, VMID width.

Cheers
Suzuki