linux-kernel - Re: [PATCH v9 03/10] arm64/kvm: expose FEAT_MTE_TAGGED

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Message-ID: <86ldppc86c.wl-maz@kernel.org>
Date: Wed, 18 Jun 2025 17:43:07 +0100
From: Marc Zyngier <maz@...nel.org>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: catalin.marinas@....com,
	pcc@...gle.com,
	will@...nel.org,
	broonie@...nel.org,
	anshuman.khandual@....com,
	joey.gouly@....com,
	yury.khrustalev@....com,
	oliver.upton@...ux.dev,
	frederic@...nel.org,
	akpm@...ux-foundation.org,
	surenb@...gle.com,
	linux-arm-kernel@...ts.infradead.org,
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	linux-doc@...r.kernel.org
Subject: Re: [PATCH v9 03/10] arm64/kvm: expose FEAT_MTE_TAGGED_FAR feature to guest

In general, please use a patch title format that matches the one used
for the subsystem. For KVM, that'd be "KVM: arm64: Expose ..."/

On Wed, 18 Jun 2025 09:45:06 +0100,
Yeoreum Yun <yeoreum.yun@....com> wrote:
> 
> expose FEAT_MTE_TAGGED_FAR feature to guest.
> 
> Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
> ---
>  arch/arm64/kvm/sys_regs.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 76c2f0da821f..c8c92cb9da01 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1586,7 +1586,7 @@ static u64 __kvm_read_sanitised_id_reg(const struct kvm_vcpu *vcpu,
>  				       const struct sys_reg_desc *r)
>  {
>  	u32 id = reg_to_encoding(r);
> -	u64 val;
> +	u64 val, mask;
>  
>  	if (sysreg_visible_as_raz(vcpu, r))
>  		return 0;
> @@ -1617,8 +1617,12 @@ static u64 __kvm_read_sanitised_id_reg(const struct kvm_vcpu *vcpu,
>  		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_MPAM_frac);
>  		break;
>  	case SYS_ID_AA64PFR2_EL1:
> -		/* We only expose FPMR */
> -		val &= ID_AA64PFR2_EL1_FPMR;
> +		mask = ID_AA64PFR2_EL1_FPMR;
> +
> +		if (kvm_has_mte(vcpu->kvm))
> +			mask |= ID_AA64PFR2_EL1_MTEFAR;
> +
> +		val &= mask;

I don't think there is a need for an extra variable, and you could
follow the pattern established in this file by writing this as:

	val &= (ID_AA64PFR2_EL1_FPMR |
		(kvm_has_mte(vcpu->kvm) ? ID_AA64PFR2_EL1_MTEFAR : 0));

Not a big deal though.

Thanks,

	M.

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