linux-kernel - Re: [PATCH v3 0/2] KVM: arm64: make EL2 feature fields writable in ID_AA64MMFR1

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Message-ID: <175828771292.1762581.13961318453079156132.b4-ty@kernel.org>
Date: Fri, 19 Sep 2025 14:15:15 +0100
From: Marc Zyngier <maz@...nel.org>
To: oliver.upton@...ux.dev,
	yuzenghui@...wei.com,
	Jinqian Yang <yangjinqian1@...wei.com>
Cc: linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	liuyonglong@...wei.com,
	wangzhou1@...ilicon.com
Subject: Re: [PATCH v3 0/2] KVM: arm64: make EL2 feature fields writable in ID_AA64MMFR1_EL1

On Thu, 11 Sep 2025 19:46:19 +0800, Jinqian Yang wrote:
> Allow userspace to downgrade EL2 features (TWED, HCX) to ensure VM live
> migration compatibility between hosts with varying feature support.
> 
> Although ID_AA64MMFR1_EL1.VH is an EL2 feature, it is still kept as non-
> writable in userspace. When FEAT_E2H0 is not implemented, HCR_EL2.E2H is
> res1. When E2H=1, EL2 operates in VHE mode. In this case, if userspace
> modifies the VH bit to 0, the Guest's kernel will still run in vEL2, leading
> to inconsistency.
> 
> [...]

Applied to next, thanks!

[1/2] KVM: arm64: Make ID_AA64MMFR1_EL1.{HCX, TWED} writable from userspace
      commit: 1a0b2bf6ff11d2e0438f3a7d1d299339edab96e8
[2/2] KVM: arm64: selftests: Test writes to ID_AA64MMFR1_EL1.{HCX, TWED}
      commit: be8c9192eaeee21fdaacd72ad4ba992b9e42377b

Cheers,

	M.
-- 
Without deviation from the norm, progress is not possible.