On 11/01/2025 00:55, Samuel Holland wrote:
> On 2025-01-06 9:48 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@xxxxxxxxxxxx>
>> ---
>> arch/riscv/kvm/vcpu.c | 3 +++
>> arch/riscv/kvm/vcpu_sbi_fwft.c | 39 ++++++++++++++++++++++++++++++++++
>> 2 files changed, 42 insertions(+)
>>
>> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
>> index 3420a4a62c94..bb6f788d46f5 100644
>> --- a/arch/riscv/kvm/vcpu.c
>> +++ b/arch/riscv/kvm/vcpu.c
>> @@ -641,6 +641,7 @@ 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;
>>
>> @@ -666,6 +667,7 @@ 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);
>> @@ -676,6 +678,7 @@ 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);
>> }
>> }
>>
>> diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/vcpu_sbi_fwft.c
>> index 55433e805baa..1e85ff6666af 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 (1UL << EXC_LOAD_MISALIGNED | 1UL << EXC_STORE_MISALIGNED)
>> +
>> static const enum sbi_fwft_feature_t kvm_fwft_defined_features[] = {
>> SBI_FWFT_MISALIGNED_EXC_DELEG,
>> SBI_FWFT_LANDING_PAD,
>> @@ -35,7 +37,44 @@ 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)
>> +{
>> + if (!unaligned_ctl_available())
>
> This seems like the wrong condition. Patch 2 requests delegation regardless of
> what probing detects. For MISALIGNED_SCALAR_FAST, the delegation likely doesn't> change any actual behavior, because the hardware likely never raises the
> exception. But it does ensure M-mode never emulates anything, so if the
> exception were to occur, the kernel has the choice whether to handle it. And
> this lets us provide the same guarantee to KVM guests. So I think this feature
> should also be supported if we successfully delegated the exception on the host
> side.
Not sure to completely follow you here but patch 2 actually does the
reverse of what you said. We request delegation from SBI *before*
probing so that allows probing to see if we (kernel) receives misaligned
accesses traps and thus set MISALIGNED_SCALAR_EMULATED.
But if I understood correctly, you mean that guest delegation should
also be available to guest in case misaligned access were delegated by
the SBI to the host which I agree. I think this condition should be
reworked to report the delegation status itself and not the misaligned
access speed that was detected
Thanks,
Clément
>
>> + return false;
>> +
>> + return true;
>> +}
>> +
>> +static int 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 int 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) != 0;
>> +
>> + 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,
>> + }
>
> nit: Please add a trailing comma here as future patches will extend the array.
>
> Regards,
> Samuel
>
>> };
>>
>> static struct kvm_sbi_fwft_config *
>
