[PATCH v6 14/14] RISC-V: KVM: add support for SBI_FWFT_MISALIGNED_DELEG

[Clément Léger]

On 09/05/2025 20:09, Atish Patra wrote:
> On 4/24/25 10:32 AM, Clément Léger wrote:
>> SBI_FWFT_MISALIGNED_DELEG needs hedeleg to be modified to delegate
>> misaligned load/store exceptions. Save and restore it during CPU
>> load/put.
>>
>> Signed-off-by: Clément Léger <cleger at rivosinc.com>
>> Reviewed-by: Deepak Gupta <debug at rivosinc.com>
>> Reviewed-by: Andrew Jones <ajones at ventanamicro.com>
>> ---
>>   arch/riscv/kvm/vcpu.c          |  3 +++
>>   arch/riscv/kvm/vcpu_sbi_fwft.c | 36 ++++++++++++++++++++++++++++++++++
>>   2 files changed, 39 insertions(+)
>>
>> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
>> index 542747e2c7f5..d98e379945c3 100644
>> --- a/arch/riscv/kvm/vcpu.c
>> +++ b/arch/riscv/kvm/vcpu.c
>> @@ -646,6 +646,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>>   {
>>       void *nsh;
>>       struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;
>> +    struct kvm_vcpu_config *cfg = &vcpu->arch.cfg;
>>         vcpu->cpu = -1;
>>   @@ -671,6 +672,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>>           csr->vstval = nacl_csr_read(nsh, CSR_VSTVAL);
>>           csr->hvip = nacl_csr_read(nsh, CSR_HVIP);
>>           csr->vsatp = nacl_csr_read(nsh, CSR_VSATP);
>> +        cfg->hedeleg = nacl_csr_read(nsh, CSR_HEDELEG);
>>       } else {
>>           csr->vsstatus = csr_read(CSR_VSSTATUS);
>>           csr->vsie = csr_read(CSR_VSIE);
>> @@ -681,6 +683,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>>           csr->vstval = csr_read(CSR_VSTVAL);
>>           csr->hvip = csr_read(CSR_HVIP);
>>           csr->vsatp = csr_read(CSR_VSATP);
>> +        cfg->hedeleg = csr_read(CSR_HEDELEG);
> 
> Can we avoid saving hedeleg in vcpu_put path by updating the cfg-
>>hedeleg in kvm_sbi_fwft_set_misaligned_delegation.
> 
> We already update the hedeleg in vcpu_load path from cfg->hedeleg.
> If the next vcpu did not enable delegation it will get the correct
> config written to hedeleg.

Yeah that make sense, I'll modify that.

Thanks,

Clément

> 
> This will save us a csr read cost in each VM exit path for something
> that is probably configured once in guest life time.>
>>       }
>>   }
>>   diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/
>> vcpu_sbi_fwft.c
>> index b0f66c7bf010..d16ee477042f 100644
>> --- a/arch/riscv/kvm/vcpu_sbi_fwft.c
>> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
>> @@ -14,6 +14,8 @@
>>   #include <asm/kvm_vcpu_sbi.h>
>>   #include <asm/kvm_vcpu_sbi_fwft.h>
>>   +#define MIS_DELEG (BIT_ULL(EXC_LOAD_MISALIGNED) |
>> BIT_ULL(EXC_STORE_MISALIGNED))
>> +
>>   struct kvm_sbi_fwft_feature {
>>       /**
>>        * @id: Feature ID
>> @@ -68,7 +70,41 @@ static bool kvm_fwft_is_defined_feature(enum
>> sbi_fwft_feature_t feature)
>>       return false;
>>   }
>>   +static bool kvm_sbi_fwft_misaligned_delegation_supported(struct
>> kvm_vcpu *vcpu)
>> +{
>> +    return misaligned_traps_can_delegate();
>> +}
>> +
>> +static long kvm_sbi_fwft_set_misaligned_delegation(struct kvm_vcpu
>> *vcpu,
>> +                    struct kvm_sbi_fwft_config *conf,
>> +                    unsigned long value)
>> +{
>> +    if (value == 1)
>> +        csr_set(CSR_HEDELEG, MIS_DELEG);
>> +    else if (value == 0)
>> +        csr_clear(CSR_HEDELEG, MIS_DELEG);
>> +    else
>> +        return SBI_ERR_INVALID_PARAM;
>> +
>> +    return SBI_SUCCESS;
>> +}
>> +
>> +static long kvm_sbi_fwft_get_misaligned_delegation(struct kvm_vcpu
>> *vcpu,
>> +                    struct kvm_sbi_fwft_config *conf,
>> +                    unsigned long *value)
>> +{
>> +    *value = (csr_read(CSR_HEDELEG) & MIS_DELEG) == MIS_DELEG;
>> +
>> +    return SBI_SUCCESS;
>> +}
>> +
>>   static const struct kvm_sbi_fwft_feature features[] = {
>> +    {
>> +        .id = SBI_FWFT_MISALIGNED_EXC_DELEG,
>> +        .supported = kvm_sbi_fwft_misaligned_delegation_supported,
>> +        .set = kvm_sbi_fwft_set_misaligned_delegation,
>> +        .get = kvm_sbi_fwft_get_misaligned_delegation,
>> +    },
>>   };
>>     static struct kvm_sbi_fwft_config *
>