Re: [PATCH 3/6] RISC-V: KVM: add SBI extension init()/deinit() functions

[Samuel Holland <samuel.holland@sifive.com>]

Hi Clément,

On 2025-01-06 9:48 AM, Clément Léger wrote:
> The FWFT SBI extension will need to dynamically allocate memory and do
> init time specific initialization. Add an init/deinit callbacks that
> allows to do so.
> 
> Signed-off-by: Clément Léger <cleger@rivosinc.com>
> ---
>  arch/riscv/include/asm/kvm_vcpu_sbi.h |  9 ++++++++
>  arch/riscv/kvm/vcpu.c                 |  2 ++
>  arch/riscv/kvm/vcpu_sbi.c             | 31 ++++++++++++++++++++++++++-
>  3 files changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
> index b96705258cf9..8c465ce90e73 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
> @@ -49,6 +49,14 @@ struct kvm_vcpu_sbi_extension {
>  
>  	/* Extension specific probe function */
>  	unsigned long (*probe)(struct kvm_vcpu *vcpu);
> +
> +	/*
> +	 * Init/deinit function called once during VCPU init/destroy. These
> +	 * might be use if the SBI extensions need to allocate or do specific
> +	 * init time only configuration.
> +	 */
> +	int (*init)(struct kvm_vcpu *vcpu);
> +	void (*deinit)(struct kvm_vcpu *vcpu);
>  };
>  
>  void kvm_riscv_vcpu_sbi_forward(struct kvm_vcpu *vcpu, struct kvm_run *run);
> @@ -69,6 +77,7 @@ const struct kvm_vcpu_sbi_extension *kvm_vcpu_sbi_find_ext(
>  bool riscv_vcpu_supports_sbi_ext(struct kvm_vcpu *vcpu, int idx);
>  int kvm_riscv_vcpu_sbi_ecall(struct kvm_vcpu *vcpu, struct kvm_run *run);
>  void kvm_riscv_vcpu_sbi_init(struct kvm_vcpu *vcpu);
> +void kvm_riscv_vcpu_sbi_deinit(struct kvm_vcpu *vcpu);
>  
>  int kvm_riscv_vcpu_get_reg_sbi_sta(struct kvm_vcpu *vcpu, unsigned long reg_num,
>  				   unsigned long *reg_val);
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index e048dcc6e65e..3420a4a62c94 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -180,6 +180,8 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
>  
>  void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
>  {
> +	kvm_riscv_vcpu_sbi_deinit(vcpu);
> +
>  	/* Cleanup VCPU AIA context */
>  	kvm_riscv_vcpu_aia_deinit(vcpu);
>  
> diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
> index 6e704ed86a83..d2dbb0762072 100644
> --- a/arch/riscv/kvm/vcpu_sbi.c
> +++ b/arch/riscv/kvm/vcpu_sbi.c
> @@ -486,7 +486,7 @@ void kvm_riscv_vcpu_sbi_init(struct kvm_vcpu *vcpu)
>  	struct kvm_vcpu_sbi_context *scontext = &vcpu->arch.sbi_context;
>  	const struct kvm_riscv_sbi_extension_entry *entry;
>  	const struct kvm_vcpu_sbi_extension *ext;
> -	int idx, i;
> +	int idx, i, ret;
>  
>  	for (i = 0; i < ARRAY_SIZE(sbi_ext); i++) {
>  		entry = &sbi_ext[i];
> @@ -501,8 +501,37 @@ void kvm_riscv_vcpu_sbi_init(struct kvm_vcpu *vcpu)
>  			continue;
>  		}
>  
> +		if (ext->init) {
> +			ret = ext->init(vcpu);
> +			if (ret)
> +				scontext->ext_status[idx] =
> +					KVM_RISCV_SBI_EXT_STATUS_UNAVAILABLE;
> +		}
> +
>  		scontext->ext_status[idx] = ext->default_disabled ?
>  					KVM_RISCV_SBI_EXT_STATUS_DISABLED :
>  					KVM_RISCV_SBI_EXT_STATUS_ENABLED;

This will overwrite the KVM_RISCV_SBI_EXT_STATUS_UNAVAILABLE set above.

>  	}
>  }
> +
> +void kvm_riscv_vcpu_sbi_deinit(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_vcpu_sbi_context *scontext = &vcpu->arch.sbi_context;
> +	const struct kvm_riscv_sbi_extension_entry *entry;
> +	const struct kvm_vcpu_sbi_extension *ext;
> +	int idx, i;
> +
> +	for (i = 0; i < ARRAY_SIZE(sbi_ext); i++) {
> +		entry = &sbi_ext[i];
> +		ext = entry->ext_ptr;
> +		idx = entry->ext_idx;
> +
> +		if (idx < 0 || idx >= ARRAY_SIZE(scontext->ext_status))
> +			continue;
> +
> +		if (scontext->ext_status[idx] != KVM_RISCV_SBI_EXT_STATUS_ENABLED || !ext->deinit)

Given that an extension can be enabled/disabled after initialization, this
should only skip deinit if the status is UNAVAILABLE.

Regards,
Samuel

> +			continue;
> +
> +		ext->deinit(vcpu);
> +	}
> +}