linux-kernel - Re: [PATCH 0/4] KVM: arm64: writable MIDR/REVIDR

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Message-ID: <Z6pCmYo3AdjDG9Di@linux.dev>
Date: Mon, 10 Feb 2025 10:16:57 -0800
From: Oliver Upton <oliver.upton@...ux.dev>
To: Sebastian Ott <sebott@...hat.com>
Cc: Marc Zyngier <maz@...nel.org>, Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
	Cornelia Huck <cohuck@...hat.com>,
	Eric Auger <eric.auger@...hat.com>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] KVM: arm64: writable MIDR/REVIDR

On Mon, Feb 10, 2025 at 04:49:49PM +0100, Sebastian Ott wrote:
> Based on prior discussion [1] this series allows VMMs to change
> MIDR/REVIDR to enable migration between machines that differ in
> these registers. Since these are used for errata handling the
> errata management series [2] is a prerequisite for this one.
> 
> Note that guest access to MIDR_EL1 is not trapped.
> 
> [1] https://lore.kernel.org/kvmarm/20250124151732.6072-1-shameerali.kolothum.thodi@huawei.com/T/#mb855bc51714095a164a7b26bb8bead1606e4b753
> [2] https://lore.kernel.org/kvmarm/20250205132222.55816-1-shameerali.kolothum.thodi@huawei.com/T/
> 
> Sebastian Ott (4):
>   KVM: arm64: Allow userspace to change MIDR_EL1
>   KVM: arm64: Allow userspace to change REVIDR_EL1
>   KVM: arm64: Allow userspace to change AIDR_EL1
>   KVM: arm64: trap guest access for REVIDR_EL1 and AIDR_EL1

Please reorganize the series such that guest accesses to REVIDR/AIDR are
trapped as soon as we allow userspace to change them. Also, can you
extend the set_id_regs selftest to assert that the guest sees the
correct value for these registers?

-- 
Thanks,
Oliver