Re: [PATCH v4 10/15] RISC-V: KVM: Support 64 bit firmware counters on RV32

[Andrew Jones]

On Wed, Feb 28, 2024 at 05:01:25PM -0800, Atish Patra wrote:
> The SBI v2.0 introduced a fw_read_hi function to read 64 bit firmware
> counters for RV32 based systems.
> 
> Add infrastructure to support that.
> 
> Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx>
> Signed-off-by: Atish Patra <atishp@xxxxxxxxxxxx>
> ---
>  arch/riscv/include/asm/kvm_vcpu_pmu.h |  4 ++-
>  arch/riscv/kvm/vcpu_pmu.c             | 37 ++++++++++++++++++++++++++-
>  arch/riscv/kvm/vcpu_sbi_pmu.c         |  6 +++++
>  3 files changed, 45 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/kvm_vcpu_pmu.h b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> index 8cb21a4f862c..e0ad27dea46c 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_pmu.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> @@ -20,7 +20,7 @@ static_assert(RISCV_KVM_MAX_COUNTERS <= 64);
>  
>  struct kvm_fw_event {
>  	/* Current value of the event */
> -	unsigned long value;
> +	u64 value;
>  
>  	/* Event monitoring status */
>  	bool started;
> @@ -91,6 +91,8 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
>  				     struct kvm_vcpu_sbi_return *retdata);
>  int kvm_riscv_vcpu_pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
>  				struct kvm_vcpu_sbi_return *retdata);
> +int kvm_riscv_vcpu_pmu_fw_ctr_read_hi(struct kvm_vcpu *vcpu, unsigned long cidx,
> +				      struct kvm_vcpu_sbi_return *retdata);
>  void kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu);
>  int kvm_riscv_vcpu_pmu_setup_snapshot(struct kvm_vcpu *vcpu, unsigned long saddr_low,
>  				      unsigned long saddr_high, unsigned long flags,
> diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> index a02f7b981005..469bb430cf97 100644
> --- a/arch/riscv/kvm/vcpu_pmu.c
> +++ b/arch/riscv/kvm/vcpu_pmu.c
> @@ -196,6 +196,29 @@ static int pmu_get_pmc_index(struct kvm_pmu *pmu, unsigned long eidx,
>  	return kvm_pmu_get_programmable_pmc_index(pmu, eidx, cbase, cmask);
>  }
>  
> +static int pmu_fw_ctr_read_hi(struct kvm_vcpu *vcpu, unsigned long cidx,
> +			      unsigned long *out_val)
> +{
> +	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> +	struct kvm_pmc *pmc;
> +	int fevent_code;
> +
> +	if (!IS_ENABLED(CONFIG_32BIT))

Let's remove the CONFIG_32BIT check in kvm_sbi_ext_pmu_handler() and then
set *out_val to zero here and return success. Either that, or we should
WARN or something here since it's a KVM bug to get here with
!CONFIG_32BIT.

> +		return -EINVAL;
> +
> +	pmc = &kvpmu->pmc[cidx];

Uh oh! We're missing range validation of cidx! And I see we're missing it
in pmu_ctr_read() too. We need the same check we have in
kvm_riscv_vcpu_pmu_ctr_info(). I think the other SBI functions are OK,
but it's worth a triple check.

> +
> +	if (pmc->cinfo.type != SBI_PMU_CTR_TYPE_FW)
> +		return -EINVAL;
> +
> +	fevent_code = get_event_code(pmc->event_idx);
> +	pmc->counter_val = kvpmu->fw_event[fevent_code].value;
> +
> +	*out_val = pmc->counter_val >> 32;
> +
> +	return 0;
> +}
> +
>  static int pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
>  			unsigned long *out_val)
>  {
> @@ -702,6 +725,18 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
>  	return 0;
>  }
>  
> +int kvm_riscv_vcpu_pmu_fw_ctr_read_hi(struct kvm_vcpu *vcpu, unsigned long cidx,
> +				      struct kvm_vcpu_sbi_return *retdata)
> +{
> +	int ret;
> +
> +	ret = pmu_fw_ctr_read_hi(vcpu, cidx, &retdata->out_val);
> +	if (ret == -EINVAL)
> +		retdata->err_val = SBI_ERR_INVALID_PARAM;
> +
> +	return 0;

I see this follows the pattern we have with kvm_riscv_vcpu_pmu_ctr_read
and pmu_ctr_read, but I wonder if we really need the
kvm_riscv_vcpu_pmu_ctr_read() and kvm_riscv_vcpu_pmu_fw_ctr_read_hi()
wrapper functions?

> +}
> +
>  int kvm_riscv_vcpu_pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
>  				struct kvm_vcpu_sbi_return *retdata)
>  {
> @@ -775,7 +810,7 @@ void kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu)
>  			pmc->cinfo.csr = CSR_CYCLE + i;
>  		} else {
>  			pmc->cinfo.type = SBI_PMU_CTR_TYPE_FW;
> -			pmc->cinfo.width = BITS_PER_LONG - 1;
> +			pmc->cinfo.width = 63;
>  		}
>  	}
>  
> diff --git a/arch/riscv/kvm/vcpu_sbi_pmu.c b/arch/riscv/kvm/vcpu_sbi_pmu.c
> index 9f61136e4bb1..58a0e5587e2a 100644
> --- a/arch/riscv/kvm/vcpu_sbi_pmu.c
> +++ b/arch/riscv/kvm/vcpu_sbi_pmu.c
> @@ -64,6 +64,12 @@ static int kvm_sbi_ext_pmu_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  	case SBI_EXT_PMU_COUNTER_FW_READ:
>  		ret = kvm_riscv_vcpu_pmu_ctr_read(vcpu, cp->a0, retdata);
>  		break;
> +	case SBI_EXT_PMU_COUNTER_FW_READ_HI:
> +		if (IS_ENABLED(CONFIG_32BIT))
> +			ret = kvm_riscv_vcpu_pmu_fw_ctr_read_hi(vcpu, cp->a0, retdata);
> +		else
> +			retdata->out_val = 0;
> +		break;
>  	case SBI_EXT_PMU_SNAPSHOT_SET_SHMEM:
>  		ret = kvm_riscv_vcpu_pmu_setup_snapshot(vcpu, cp->a0, cp->a1, cp->a2, retdata);
>  		break;
> -- 
> 2.34.1
> 

Thanks,
drew