linux-kernel - Re: [PATCH v3 4/6] KVM: arm64: show writable masks for feature registers

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Date: Wed, 29 May 2024 15:49:28 +0200
From: Eric Auger <eauger@...hat.com>
To: Sebastian Ott <sebott@...hat.com>, linux-arm-kernel@...ts.infradead.org,
 kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
 James Morse <james.morse@....com>, Suzuki K Poulose
 <suzuki.poulose@....com>, Catalin Marinas <catalin.marinas@....com>,
 Will Deacon <will@...nel.org>
Subject: Re: [PATCH v3 4/6] KVM: arm64: show writable masks for feature
 registers

Hi Sebastian,

On 5/14/24 09:22, Sebastian Ott wrote:
> Instead of using ~0UL provide the actual writable mask for
> non-id feature registers in the output of the
> KVM_ARM_GET_REG_WRITABLE_MASKS ioctl.
> 
> This changes the mask for the CTR_EL0 and CLIDR_EL1 registers.
> 
> Signed-off-by: Sebastian Ott <sebott@...hat.com>
> ---
>  arch/arm64/kvm/sys_regs.c | 19 +++++--------------
>  1 file changed, 5 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 8e8acf3dd9bd..1b6ab483e21e 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -2562,7 +2562,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  
>  	{ SYS_DESC(SYS_CCSIDR_EL1), access_ccsidr },
>  	{ SYS_DESC(SYS_CLIDR_EL1), access_clidr, reset_clidr, CLIDR_EL1,
> -	  .set_user = set_clidr },
> +	  .set_user = set_clidr, .val = ~CLIDR_EL1_RES0 },
>  	{ SYS_DESC(SYS_CCSIDR2_EL1), undef_access },
>  	{ SYS_DESC(SYS_SMIDR_EL1), undef_access },
>  	{ SYS_DESC(SYS_CSSELR_EL1), access_csselr, reset_unknown, CSSELR_EL1 },
> @@ -4121,20 +4121,11 @@ int kvm_vm_ioctl_get_reg_writable_masks(struct kvm *kvm, struct reg_mask_range *
>  		if (!is_feature_id_reg(encoding) || !reg->set_user)
>  			continue;
>  
> -		/*
> -		 * For ID registers, we return the writable mask. Other feature
> -		 * registers return a full 64bit mask. That's not necessary
> -		 * compliant with a given revision of the architecture, but the
> -		 * RES0/RES1 definitions allow us to do that.
> -		 */
> -		if (is_vm_ftr_id_reg(encoding)) {
> -			if (!reg->val ||
> -			    (is_aa32_id_reg(encoding) && !kvm_supports_32bit_el0()))
> -				continue;
> -			val = reg->val;
> -		} else {
> -			val = ~0UL;
> +		if (!reg->val ||
> +		    (is_aa32_id_reg(encoding) && !kvm_supports_32bit_el0())) {
> +			continue;
>  		}
> +		val = reg->val;
>  
>  		if (put_user(val, (masks + KVM_ARM_FEATURE_ID_RANGE_INDEX(encoding))))
>  			return -EFAULT;
Reviewed-by: Eric Auger <eric.auger@...hat.com>

Eric