linux-kernel - Re: [PATCH v2 06/11] KVM: arm64: hide MOPS from guests

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Message-ID: <b38910d2-a675-88d9-985c-adf527c08045@arm.com>
Date:   Tue, 30 May 2023 17:34:34 +0100
From:   Kristina Martsenko <kristina.martsenko@....com>
To:     Colton Lewis <coltonlewis@...gle.com>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        Luis Machado <luis.machado@....com>,
        Vladimir Murzin <vladimir.murzin@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 06/11] KVM: arm64: hide MOPS from guests

On 25/05/2023 20:26, Colton Lewis wrote:
>> As FEAT_MOPS is not supported in guests yet, hide it from the ID
>> registers for guests.
> 
>> The MOPS instructions are UNDEFINED in guests as HCRX_EL2.MSCEn is not
>> set in HCRX_GUEST_FLAGS, and will take an exception to EL1 if executed.
> 
> For my benefit, could you please explain why no support for guests yet?
> Why not set HCRX_EL2.MSCEn in this series?

There's probably a few more things that need doing for guest support, such as 
setting the HCRX_EL2.MCE2 bit and handling the mops exception in KVM. I'm
currently having a look at guest support.

Thanks,
Kristina