Re: [PATCH 2/5] KVM: arm64: Refactor filtering of ID registers

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On Sun, 16 Feb 2020 18:53:21 +0000
Marc Zyngier <maz@xxxxxxxxxx> wrote:

Hi,

> 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.

Indeed, much better now.

> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>

Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>

Thanks,
Andre

> ---
>  arch/arm64/kvm/sys_regs.c | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index da82c4b03aab..682fedd7700f 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -9,6 +9,7 @@
>   *          Christoffer Dall <c.dall@xxxxxxxxxxxxxxxxxxxxxx>
>   */
>  
> +#include <linux/bitfield.h>
>  #include <linux/bsearch.h>
>  #include <linux/kvm_host.h>
>  #include <linux/mm.h>
> @@ -1070,6 +1071,8 @@ 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)
> @@ -1078,13 +1081,18 @@ 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 && !vcpu_has_sve(vcpu)) {
> -		val &= ~(0xfUL << ID_AA64PFR0_SVE_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));
> +	switch (id) {
> +	case SYS_ID_AA64PFR0_EL1:
> +		if (!vcpu_has_sve(vcpu))
> +			val &= ~FEATURE(ID_AA64PFR0_SVE);
> +		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;
>  	}
>  
>  	return val;

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