linux-kernel - Re: [PATCH 2/3] arm64/kvm: Fine grain _EL2 system registers list that affect nested virtualization

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Message-ID: <868r93es5a.wl-maz@kernel.org>
Date:   Mon, 18 Sep 2023 10:40:17 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Miguel Luis <miguel.luis@...cle.com>
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>,
        Zenghui Yu <yuzenghui@...wei.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.linux.dev
Subject: Re: [PATCH 2/3] arm64/kvm: Fine grain _EL2 system registers list that affect nested virtualization

Hi Miguel,

On Wed, 13 Sep 2023 19:52:07 +0100,
Miguel Luis <miguel.luis@...cle.com> wrote:
> 
> Some _EL1 registers got included in the _EL2 ranges, which are not
> affected by NV. Remove them and fine grain the ranges to exclusively
> include the _EL2 ones.
> 
> Signed-off-by: Miguel Luis <miguel.luis@...cle.com>
> ---
>  arch/arm64/kvm/emulate-nested.c | 44 ++++++++++++++++++++++++++++-----
>  1 file changed, 38 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
> index 9ced1bf0c2b7..9aa1c06abdb7 100644
> --- a/arch/arm64/kvm/emulate-nested.c
> +++ b/arch/arm64/kvm/emulate-nested.c
> @@ -649,14 +649,46 @@ static const struct encoding_to_trap_config encoding_to_cgt[] __initconst = {
>  	SR_TRAP(SYS_APGAKEYHI_EL1,	CGT_HCR_APK),
>  	/* All _EL2 registers */
>  	SR_RANGE_TRAP(sys_reg(3, 4, 0, 0, 0),
> -		      sys_reg(3, 4, 3, 15, 7), CGT_HCR_NV),
> +			sys_reg(3, 4, 4, 0, 1), CGT_HCR_NV),

It would be good if the commit message explained that you are folding
SPSR/ELR into the existing range. Also, please keep the two ends of
the ranges vertically aligned.

>  	/* Skip the SP_EL1 encoding... */
> -	SR_TRAP(SYS_SPSR_EL2,		CGT_HCR_NV),
> -	SR_TRAP(SYS_ELR_EL2,		CGT_HCR_NV),
> -	SR_RANGE_TRAP(sys_reg(3, 4, 4, 1, 1),
> -		      sys_reg(3, 4, 10, 15, 7), CGT_HCR_NV),
> +	SR_RANGE_TRAP(sys_reg(3, 4, 4, 3, 0),
> +			sys_reg(3, 4, 10, 6, 7), CGT_HCR_NV),
> +	/* skip MECID_A0_EL2, MECID_A1_EL2, MECID_P0_EL2,
> +	 *      MECID_P1_EL2, MECIDR_EL2, VMECID_A_EL2,
> +	 *      VMECID_P_EL2.
> +	 */

Please follow the kernel comment format. Also, why are you skipping
the MEC registers, but not the MPAM ones? At least indicate a
rationale for this.

>  	SR_RANGE_TRAP(sys_reg(3, 4, 12, 0, 0),
> -		      sys_reg(3, 4, 14, 15, 7), CGT_HCR_NV),
> +			sys_reg(3, 4, 12, 1, 1), CGT_HCR_NV),
> +	/* ICH_AP0R<m>_EL2 */
> +	SR_RANGE_TRAP(SYS_ICH_AP0R0_EL2,
> +			SYS_ICH_AP0R3_EL2, CGT_HCR_NV),
> +	/* ICH_AP1R<m>_EL2 */
> +	SR_RANGE_TRAP(SYS_ICH_AP1R0_EL2,
> +			SYS_ICH_AP1R3_EL2, CGT_HCR_NV),
> +	SR_RANGE_TRAP(sys_reg(3, 4, 12, 9, 5),
> +			sys_reg(3, 4, 12, 11, 7), CGT_HCR_NV),
> +	/* ICH_LR<m>_EL2 */
> +	SR_TRAP(SYS_ICH_LR0_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR1_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR2_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR3_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR4_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR5_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR6_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR7_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR8_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR9_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR10_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR11_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR12_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR13_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR14_EL2,	CGT_HCR_NV),
> +	SR_TRAP(SYS_ICH_LR15_EL2,	CGT_HCR_NV),

You could describe all the LRs a single range.

> +	SR_RANGE_TRAP(sys_reg(3, 4, 13, 0, 1),
> +			sys_reg(3, 4, 13, 0, 7), CGT_HCR_NV),
> +	/* skip AMEVCNTVOFF0<n>_EL2 and AMEVCNTVOFF1<n>_EL2 */

Why?

> +	SR_RANGE_TRAP(sys_reg(3, 4, 14, 0, 3),
> +			sys_reg(3, 4, 14, 5, 2), CGT_HCR_NV),
>  	/* All _EL02, _EL12 registers */
>  	SR_RANGE_TRAP(sys_reg(3, 5, 0, 0, 0),
>  		      sys_reg(3, 5, 10, 15, 7), CGT_HCR_NV),

Thanks,

	M.

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