Re: [RFC PATCH v4 4/5] RISC-V: KVM: add support for SBI_FWFT_PTE_AD_HW_UPDATING

[Clément Léger]

On 24/05/2024 12:33, Yong-Xuan Wang wrote:
> Add support for SBI_FWFT_PTE_AD_HW_UPDATING to set the PTE A/D bits
> updating behavior for Guest/VM.
> 
> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@xxxxxxxxxx>
> ---
>  arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h |  2 +-
>  arch/riscv/kvm/vcpu_sbi_fwft.c             | 38 +++++++++++++++++++++-
>  2 files changed, 38 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
> index 7b7bcc5c8fee..3614a44e0a4a 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi_fwft.h
> @@ -11,7 +11,7 @@
>  
>  #include <asm/sbi.h>
>  
> -#define KVM_SBI_FWFT_FEATURE_COUNT	1
> +#define KVM_SBI_FWFT_FEATURE_COUNT	2
>  
>  struct kvm_sbi_fwft_config;
>  struct kvm_vcpu;
> diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/vcpu_sbi_fwft.c
> index 89ec263c250d..14ef74023340 100644
> --- a/arch/riscv/kvm/vcpu_sbi_fwft.c
> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
> @@ -71,6 +71,36 @@ static int kvm_sbi_fwft_get_misaligned_delegation(struct kvm_vcpu *vcpu,
>  	return SBI_SUCCESS;
>  }
>  
> +static int kvm_sbi_fwft_adue_supported(struct kvm_vcpu *vcpu)
> +{
> +	if (!riscv_isa_extension_available(vcpu->arch.isa, SVADU))
> +		return SBI_ERR_NOT_SUPPORTED;
> +
> +	return 0;
> +}
> +
> +static int kvm_sbi_fwft_set_adue(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf,
> +				 unsigned long value)
> +{
> +	if (value)
> +		vcpu->arch.cfg.henvcfg |= ENVCFG_ADUE;
> +	else
> +		vcpu->arch.cfg.henvcfg &= ~ENVCFG_ADUE;
> +
> +	return SBI_SUCCESS;
> +}
> +
> +static int kvm_sbi_fwft_get_adue(struct kvm_vcpu *vcpu, struct kvm_sbi_fwft_config *conf,
> +				 unsigned long *value)
> +{
> +	if (!riscv_isa_extension_available(vcpu->arch.isa, SVADU))
> +		return SBI_ERR_NOT_SUPPORTED;
> +
> +	*value = !!(vcpu->arch.cfg.henvcfg & ENVCFG_ADUE);
> +
> +	return SBI_SUCCESS;
> +}

Hi Yong-Xuan,

vcpu->arch.cfg.henvcfg seems to be used to update the HENVCFG CSR  only
during vcpu_load()/vcpu_put(). So if this extension updates it there and
stays in the execution loop (kvm_arch_vcpu_ioctl_run()) then, it seems
like the HENVCFG CSR won't be updated immediately but on the next
vcpu_load(). Is there something I'm missing ?

Thanks,

Clément Léger

> +
>  static struct kvm_sbi_fwft_config *
>  kvm_sbi_fwft_get_config(struct kvm_vcpu *vcpu, enum sbi_fwft_feature_t feature)
>  {
> @@ -177,7 +207,13 @@ static const struct kvm_sbi_fwft_feature features[] = {
>  		.supported = kvm_sbi_fwft_misaligned_delegation_supported,
>  		.set = kvm_sbi_fwft_set_misaligned_delegation,
>  		.get = kvm_sbi_fwft_get_misaligned_delegation,
> -	}
> +	},
> +	{
> +		.id = SBI_FWFT_PTE_AD_HW_UPDATING,
> +		.supported = kvm_sbi_fwft_adue_supported,
> +		.set = kvm_sbi_fwft_set_adue,
> +		.get = kvm_sbi_fwft_get_adue,
> +	},
>  };
>  
>  static_assert(ARRAY_SIZE(features) == KVM_SBI_FWFT_FEATURE_COUNT);