Re: [PATCH 4/6] KVM: arm64: Refactor filtering of ID registers

From: Auger Eric <eric.auger@redhat.com>
To: Marc Zyngier <maz@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org
Cc: James Morse <james.morse@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	kernel-team@android.com
Subject: Re: [PATCH 4/6] KVM: arm64: Refactor filtering of ID registers
Date: Fri, 15 Jan 2021 14:31:57 +0100	[thread overview]
Message-ID: <143efd5f-0641-8ed1-f055-df6e1d5216d8@redhat.com> (raw)
In-Reply-To: <20210114105633.2558739-5-maz@kernel.org>

Hi Marc,

On 1/14/21 11:56 AM, Marc Zyngier wrote:
> Our current ID register filtering is starting to be a mess of if()
> statements, and isn't going to get any saner.
> 
> Let's turn it into a switch(), which has a chance of being more
> readable, and introduce a FEATURE() macro that allows easy generation
> of feature masks.
> 
> No functionnal change intended.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>

> ---
>  arch/arm64/kvm/sys_regs.c | 51 +++++++++++++++++++++------------------
>  1 file changed, 28 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 2bea0494b81d..dda16d60197b 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -9,6 +9,7 @@
>   *          Christoffer Dall <c.dall@virtualopensystems.com>
>   */
>  
> +#include <linux/bitfield.h>
>  #include <linux/bsearch.h>
>  #include <linux/kvm_host.h>
>  #include <linux/mm.h>
> @@ -1016,6 +1017,8 @@ static bool access_arch_timer(struct kvm_vcpu *vcpu,
>  	return true;
>  }
>  
> +#define FEATURE(x)	(GENMASK_ULL(x##_SHIFT + 3, x##_SHIFT))
> +
>  /* Read a sanitised cpufeature ID register by sys_reg_desc */
>  static u64 read_id_reg(const struct kvm_vcpu *vcpu,
>  		struct sys_reg_desc const *r, bool raz)
> @@ -1024,36 +1027,38 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
>  			 (u32)r->CRn, (u32)r->CRm, (u32)r->Op2);
>  	u64 val = raz ? 0 : read_sanitised_ftr_reg(id);
>  
> -	if (id == SYS_ID_AA64PFR0_EL1) {
> +	switch (id) {
> +	case SYS_ID_AA64PFR0_EL1:
>  		if (!vcpu_has_sve(vcpu))
> -			val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
> -		val &= ~(0xfUL << ID_AA64PFR0_AMU_SHIFT);
> -		val &= ~(0xfUL << ID_AA64PFR0_CSV2_SHIFT);
> -		val |= ((u64)vcpu->kvm->arch.pfr0_csv2 << ID_AA64PFR0_CSV2_SHIFT);
> -		val &= ~(0xfUL << ID_AA64PFR0_CSV3_SHIFT);
> -		val |= ((u64)vcpu->kvm->arch.pfr0_csv3 << ID_AA64PFR0_CSV3_SHIFT);
> -	} else if (id == SYS_ID_AA64PFR1_EL1) {
> -		val &= ~(0xfUL << ID_AA64PFR1_MTE_SHIFT);
> -	} else if (id == SYS_ID_AA64ISAR1_EL1 && !vcpu_has_ptrauth(vcpu)) {
> -		val &= ~((0xfUL << ID_AA64ISAR1_APA_SHIFT) |
> -			 (0xfUL << ID_AA64ISAR1_API_SHIFT) |
> -			 (0xfUL << ID_AA64ISAR1_GPA_SHIFT) |
> -			 (0xfUL << ID_AA64ISAR1_GPI_SHIFT));
> -	} else if (id == SYS_ID_AA64DFR0_EL1) {
> -		u64 cap = 0;
> -
> +			val &= ~FEATURE(ID_AA64PFR0_SVE);
> +		val &= ~FEATURE(ID_AA64PFR0_AMU);
> +		val &= ~FEATURE(ID_AA64PFR0_CSV2);
> +		val |= FIELD_PREP(FEATURE(ID_AA64PFR0_CSV2), (u64)vcpu->kvm->arch.pfr0_csv2);
> +		val &= ~FEATURE(ID_AA64PFR0_CSV3);
> +		val |= FIELD_PREP(FEATURE(ID_AA64PFR0_CSV3), (u64)vcpu->kvm->arch.pfr0_csv3);
> +		break;
> +	case SYS_ID_AA64PFR1_EL1:
> +		val &= ~FEATURE(ID_AA64PFR1_MTE);
> +		break;
> +	case SYS_ID_AA64ISAR1_EL1:
> +		if (!vcpu_has_ptrauth(vcpu))
> +			val &= ~(FEATURE(ID_AA64ISAR1_APA) |
> +				 FEATURE(ID_AA64ISAR1_API) |
> +				 FEATURE(ID_AA64ISAR1_GPA) |
> +				 FEATURE(ID_AA64ISAR1_GPI));
> +		break;
> +	case SYS_ID_AA64DFR0_EL1:
>  		/* Limit guests to PMUv3 for ARMv8.1 */
> -		if (kvm_vcpu_has_pmu(vcpu))
> -			cap = ID_AA64DFR0_PMUVER_8_1;
> -
>  		val = cpuid_feature_cap_perfmon_field(val,
> -						ID_AA64DFR0_PMUVER_SHIFT,
> -						cap);
so you did the change evoked in my previous comment here.
> -	} else if (id == SYS_ID_DFR0_EL1) {
> +						      ID_AA64DFR0_PMUVER_SHIFT,
> +						      kvm_vcpu_has_pmu(vcpu) ? ID_AA64DFR0_PMUVER_8_1 : 0);
> +		break;
> +	case SYS_ID_DFR0_EL1:
>  		/* Limit guests to PMUv3 for ARMv8.1 */
>  		val = cpuid_feature_cap_perfmon_field(val,
>  						      ID_DFR0_PERFMON_SHIFT,
>  						      kvm_vcpu_has_pmu(vcpu) ? ID_DFR0_PERFMON_8_1 : 0);
> +		break;
>  	}
>  
>  	return val;
> 
Looks indeed more readable

Reviewed-by: Eric Auger <eric.auger@redhat.com>

Eric