linux-kernel - Re: [PATCH v6 2/5] KVM: arm64: Add newly allocated ID registers to register descriptions

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Date: Sun, 31 Mar 2024 11:59:06 +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>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Jonathan Corbet <corbet@....net>,
	Shuah Khan <shuah@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Dave Martin <Dave.Martin@....com>,
	kvmarm@...ts.linux.dev,
	linux-doc@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v6 2/5] KVM: arm64: Add newly allocated ID registers to register descriptions

On Fri, 29 Mar 2024 00:13:43 +0000,
Mark Brown <broonie@...nel.org> wrote:
> 
> The 2023 architecture extensions have allocated some new ID registers, add
> them to the KVM system register descriptions so that they are visible to
> guests.
> 
> We make the newly introduced dpISA features writeable, as well as
> allowing writes to ID_AA64ISAR3_EL1.CPA for FEAT_CPA which only
> introduces straigforward new instructions with no additional
> architectural state or traps.

FPMR actively gets trapped by HCRX_EL2.

> 
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index c9f4f387155f..a3c20d1a36aa 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -2293,12 +2293,15 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  		   ID_AA64PFR0_EL1_AdvSIMD |
>  		   ID_AA64PFR0_EL1_FP), },
>  	ID_SANITISED(ID_AA64PFR1_EL1),
> -	ID_UNALLOCATED(4,2),
> +	ID_WRITABLE(ID_AA64PFR2_EL1, ~(ID_AA64PFR2_EL1_RES0 |
> +				       ID_AA64PFR2_EL1_MTEFAR |
> +				       ID_AA64PFR2_EL1_MTESTOREONLY |
> +				       ID_AA64PFR2_EL1_MTEPERM)),
>  	ID_UNALLOCATED(4,3),
>  	ID_WRITABLE(ID_AA64ZFR0_EL1, ~ID_AA64ZFR0_EL1_RES0),
>  	ID_HIDDEN(ID_AA64SMFR0_EL1),
>  	ID_UNALLOCATED(4,6),
> -	ID_UNALLOCATED(4,7),
> +	ID_WRITABLE(ID_AA64FPFR0_EL1, ~ID_AA64FPFR0_EL1_RES0),
>  
>  	/* CRm=5 */
>  	{ SYS_DESC(SYS_ID_AA64DFR0_EL1),
> @@ -2325,7 +2328,9 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  	ID_WRITABLE(ID_AA64ISAR2_EL1, ~(ID_AA64ISAR2_EL1_RES0 |
>  					ID_AA64ISAR2_EL1_APA3 |
>  					ID_AA64ISAR2_EL1_GPA3)),
> -	ID_UNALLOCATED(6,3),
> +	ID_WRITABLE(ID_AA64ISAR3_EL1, ~(ID_AA64ISAR2_EL1_RES0 |
> +					ID_AA64ISAR3_EL1_PACM |
> +					ID_AA64ISAR3_EL1_TLBIW)),
>  	ID_UNALLOCATED(6,4),
>  	ID_UNALLOCATED(6,5),
>  	ID_UNALLOCATED(6,6),
> 

Where is the code that enforces the lack of support for MTEFAR,
MTESTOREONLY, and MTEPERM for SCTLR_ELx, EnPACM and EnFPM in HCRX_EL2?
And I haven't checked whether TLBI VMALLWS2 can be trapped.

	M.

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