linux-kernel - Re: [PATCH v14 3/5] KVM: arm64: Manage GCS access and registers for guests

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Message-ID: <87iku6vl4z.wl-maz@kernel.org>
Date: Sat, 05 Oct 2024 12:34:20 +0100
From: Marc Zyngier <maz@...nel.org>
To: Mark Brown <broonie@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Shuah Khan <shuah@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org,
	kvmarm@...ts.linux.dev,
	linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v14 3/5] KVM: arm64: Manage GCS access and registers for guests

On Sat, 05 Oct 2024 11:37:30 +0100,
Mark Brown <broonie@...nel.org> wrote:
> 
> GCS introduces a number of system registers for EL1 and EL0, 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.  Also enable fine grained traps for
> access to the GCS registers by guests which do not have the feature
> enabled.
> 
> In order to allow userspace to control availability of the feature to
> guests we enable writability for only ID_AA64PFR1_EL1.GCS, this is a
> deliberately conservative choice to avoid errors due to oversights.
> Further fields should be made writable in future.

It appears I have accidentally dropped the branch fixing
ID_AA64PFR1_EL1.  I'll make sure this goes in as quickly as possible.


> 
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>  arch/arm64/include/asm/kvm_host.h          | 12 ++++++++++++
>  arch/arm64/include/asm/vncr_mapping.h      |  2 ++
>  arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 31 ++++++++++++++++++++++++++++++
>  arch/arm64/kvm/sys_regs.c                  | 31 +++++++++++++++++++++++++++++-
>  4 files changed, 75 insertions(+), 1 deletion(-)
>

[...]

> @@ -4716,6 +4737,14 @@ void kvm_calculate_traps(struct kvm_vcpu *vcpu)
>  		kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nPOR_EL1 |
>  						HFGxTR_EL2_nPOR_EL0);
>  
> +	if (!kvm_has_gcs(kvm)) {
> +		kvm->arch.fgu[HFGxTR_GROUP] |= (HFGxTR_EL2_nGCS_EL0 |
> +						HFGxTR_EL2_nGCS_EL1);
> +		kvm->arch.fgu[HFGITR_GROUP] |= (HFGITR_EL2_nGCSEPP |
> +						HFGITR_EL2_nGCSSTR_EL1 |
> +						HFGITR_EL2_nGCSPUSHM_EL1);

Where is the handling of traps resulting of HFGITR_EL2.nGCSSTR_EL1?

	M.

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