Re: [PATCH 7/8] RISC-V: KVM: Implement get event info function

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

Hi Atish,

On 2024-11-19 2:29 PM, Atish Patra wrote:
> The new get_event_info funciton allows the guest to query the presence
> of multiple events with single SBI call. Currently, the perf driver
> in linux guest invokes it for all the standard SBI PMU events. Support
> the SBI function implementation in KVM as well.
> 
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
> ---
>  arch/riscv/include/asm/kvm_vcpu_pmu.h |  3 ++
>  arch/riscv/kvm/vcpu_pmu.c             | 67 +++++++++++++++++++++++++++++++++++
>  arch/riscv/kvm/vcpu_sbi_pmu.c         |  3 ++
>  3 files changed, 73 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/kvm_vcpu_pmu.h b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> index 1d85b6617508..9a930afc8f57 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_pmu.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> @@ -98,6 +98,9 @@ void kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu);
>  int kvm_riscv_vcpu_pmu_snapshot_set_shmem(struct kvm_vcpu *vcpu, unsigned long saddr_low,
>  				      unsigned long saddr_high, unsigned long flags,
>  				      struct kvm_vcpu_sbi_return *retdata);
> +int kvm_riscv_vcpu_pmu_event_info(struct kvm_vcpu *vcpu, unsigned long saddr_low,
> +				  unsigned long saddr_high, unsigned long num_events,
> +				  unsigned long flags, struct kvm_vcpu_sbi_return *retdata);
>  void kvm_riscv_vcpu_pmu_deinit(struct kvm_vcpu *vcpu);
>  void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu);
>  
> diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> index efd66835c2b8..a30f7ec31479 100644
> --- a/arch/riscv/kvm/vcpu_pmu.c
> +++ b/arch/riscv/kvm/vcpu_pmu.c
> @@ -456,6 +456,73 @@ int kvm_riscv_vcpu_pmu_snapshot_set_shmem(struct kvm_vcpu *vcpu, unsigned long s
>  	return 0;
>  }
>  
> +int kvm_riscv_vcpu_pmu_event_info(struct kvm_vcpu *vcpu, unsigned long saddr_low,
> +				  unsigned long saddr_high, unsigned long num_events,
> +				  unsigned long flags, struct kvm_vcpu_sbi_return *retdata)
> +{
> +	unsigned long hva;
> +	struct riscv_pmu_event_info *einfo;
> +	int shmem_size = num_events * sizeof(*einfo);
> +	bool writable;
> +	gpa_t shmem;
> +	u32 eidx, etype;
> +	u64 econfig;
> +	int ret;
> +
> +	if (flags != 0 || (saddr_low & (SZ_16 - 1))) {
> +		ret = SBI_ERR_INVALID_PARAM;
> +		goto out;
> +	}
> +
> +	shmem = saddr_low;
> +	if (saddr_high != 0) {
> +		if (IS_ENABLED(CONFIG_32BIT)) {
> +			shmem |= ((gpa_t)saddr_high << 32);
> +		} else {
> +			ret = SBI_ERR_INVALID_ADDRESS;
> +			goto out;
> +		}
> +	}
> +
> +	hva = kvm_vcpu_gfn_to_hva_prot(vcpu, shmem >> PAGE_SHIFT, &writable);
> +	if (kvm_is_error_hva(hva) || !writable) {
> +		ret = SBI_ERR_INVALID_ADDRESS;

This only checks the first page if the address crosses a page boundary. Maybe
that is okay since kvm_vcpu_read_guest()/kvm_vcpu_write_guest() will fail if a
later page is inaccessible?

> +		goto out;
> +	}
> +
> +	einfo = kzalloc(shmem_size, GFP_KERNEL);
> +	if (!einfo)
> +		return -ENOMEM;
> +
> +	ret = kvm_vcpu_read_guest(vcpu, shmem, einfo, shmem_size);
> +	if (ret) {
> +		ret = SBI_ERR_FAILURE;
> +		goto free_mem;
> +	}
> +
> +	for (int i = 0; i < num_events; i++) {
> +		eidx = einfo[i].event_idx;
> +		etype = kvm_pmu_get_perf_event_type(eidx);
> +		econfig = kvm_pmu_get_perf_event_config(eidx, einfo[i].event_data);
> +		ret = riscv_pmu_get_event_info(etype, econfig, NULL);
> +		if (ret > 0)
> +			einfo[i].output = 1;

This also needs to write `output` in the else case to indicate that the event is
not supported; the spec does not require the caller to initialize bit 0 of
output to zero.

Regards,
Samuel

> +	}
> +
> +	kvm_vcpu_write_guest(vcpu, shmem, einfo, shmem_size);
> +	if (ret) {
> +		ret = SBI_ERR_FAILURE;
> +		goto free_mem;
> +	}
> +
> +free_mem:
> +	kfree(einfo);
> +out:
> +	retdata->err_val = ret;
> +
> +	return 0;
> +}
> +
>  int kvm_riscv_vcpu_pmu_num_ctrs(struct kvm_vcpu *vcpu,
>  				struct kvm_vcpu_sbi_return *retdata)
>  {
> diff --git a/arch/riscv/kvm/vcpu_sbi_pmu.c b/arch/riscv/kvm/vcpu_sbi_pmu.c
> index e4be34e03e83..a020d979d179 100644
> --- a/arch/riscv/kvm/vcpu_sbi_pmu.c
> +++ b/arch/riscv/kvm/vcpu_sbi_pmu.c
> @@ -73,6 +73,9 @@ static int kvm_sbi_ext_pmu_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  	case SBI_EXT_PMU_SNAPSHOT_SET_SHMEM:
>  		ret = kvm_riscv_vcpu_pmu_snapshot_set_shmem(vcpu, cp->a0, cp->a1, cp->a2, retdata);
>  		break;
> +	case SBI_EXT_PMU_EVENT_GET_INFO:
> +		ret = kvm_riscv_vcpu_pmu_event_info(vcpu, cp->a0, cp->a1, cp->a2, cp->a3, retdata);
> +		break;
>  	default:
>  		retdata->err_val = SBI_ERR_NOT_SUPPORTED;
>  	}
>