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

["Clément Léger" <cleger@rivosinc.com>]

On 11/01/2025 00:42, Samuel Holland wrote:
> 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.

Oh yes indeed, I should add a "continue" under the if 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.

yeah, make sense as well,

Thanks for the review,

Clément

> 
> Regards,
> Samuel
> 
>> +			continue;
>> +
>> +		ext->deinit(vcpu);
>> +	}
>> +}
>