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From: Leonardo Bras <leo.bras@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: Leonardo Bras <leo.bras@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Marc Zyngier <maz@kernel.org>,
	Joey Gouly <joey.gouly@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Shuah Khan <shuah@kernel.org>,
	Oliver Upton <oupton@kernel.org>,
	Fuad Tabba <fuad.tabba@linux.dev>,
	Peter Maydell <peter.maydell@linaro.org>,
	Wei-Lin Chang <weilin.chang@arm.com>,
	Yao Yuan <yaoyuan@linux.alibaba.com>,
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	linux-doc@vger.kernel.org,
	kvmarm@lists.linux.dev,
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Subject: Re: [PATCH v20 03/14] KVM: arm64: Manage GCS access and registers for guests
Date: Wed,  2 Sep 2026 17:44:18 +0100
Message-ID: <aphSYqKrgUq5Qycu@LeoBrasDK>
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Hi Mark,

On Tue, Sep 01, 2026 at 10:47:01PM +0100, Mark Brown wrote:
> GCS introduces a number of system registers, on systems with GCS we need
> to context switch them and expose them to VMMs to allow guests to use
> GCS.
> 
> In order to allow guests to use GCS we also need to configure
> HCRX_EL2.GCSEn, if this is not set GCS instructions will be noops and
> CHKFEAT will report GCS as disabled.
> 

Everything you do seems the correct approach, and all the loads/saves 
are symmetrical, except for VEL2, for which the reason was made known 
in v19 discussion.

That being said, I may have missed something as I am still not very much 
used to NV code. So, FWIW:

Reviewed-by: Leonardo Bras <leo.bras@arm.com>

Nit:
Reading this patch, it feels like it should have been two different 
patches: one for adding the registers to kvm infra, and the other for 
loading/saving it in the code (with GCSEn). If you later decide to split 
it, feel free to add my R-b in both of them.

Thanks!
Leo