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

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Message-ID: <20200415142237.651114f7@why>
Date:   Wed, 15 Apr 2020 14:22:37 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
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 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.

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