Re: [PATCH v2 07/11] RISC-V: KVM: Add SBI PMU extension support

[Andrew Jones]

On Thu, Dec 15, 2022 at 09:00:42AM -0800, Atish Patra wrote:
> SBI PMU extension allows KVM guests to configure/start/stop/query about
> the PMU counters in virtualized enviornment as well.
> 
> In order to allow that, KVM implements the entire SBI PMU extension.
> 
> Signed-off-by: Atish Patra <atishp@xxxxxxxxxxxx>
> ---
>  arch/riscv/kvm/Makefile       |  2 +-
>  arch/riscv/kvm/vcpu_sbi.c     | 11 +++++
>  arch/riscv/kvm/vcpu_sbi_pmu.c | 86 +++++++++++++++++++++++++++++++++++
>  3 files changed, 98 insertions(+), 1 deletion(-)
>  create mode 100644 arch/riscv/kvm/vcpu_sbi_pmu.c
> 
> diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
> index 5de1053..278e97c 100644
> --- a/arch/riscv/kvm/Makefile
> +++ b/arch/riscv/kvm/Makefile
> @@ -25,4 +25,4 @@ kvm-y += vcpu_sbi_base.o
>  kvm-y += vcpu_sbi_replace.o
>  kvm-y += vcpu_sbi_hsm.o
>  kvm-y += vcpu_timer.o
> -kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_pmu.o
> +kvm-$(CONFIG_RISCV_PMU_SBI) += vcpu_pmu.o vcpu_sbi_pmu.o
> diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
> index 50c5472..3b8b84e8 100644
> --- a/arch/riscv/kvm/vcpu_sbi.c
> +++ b/arch/riscv/kvm/vcpu_sbi.c
> @@ -20,6 +20,16 @@ static const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_v01 = {
>  };
>  #endif
>  
> +#ifdef CONFIG_RISCV_PMU_SBI
> +extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pmu;
> +#else
> +static const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pmu = {
> +	.extid_start = -1UL,
> +	.extid_end = -1UL,
> +	.handler = NULL,
> +};
> +#endif
> +
>  static const struct kvm_vcpu_sbi_extension *sbi_ext[] = {
>  	&vcpu_sbi_ext_v01,
>  	&vcpu_sbi_ext_base,
> @@ -28,6 +38,7 @@ static const struct kvm_vcpu_sbi_extension *sbi_ext[] = {
>  	&vcpu_sbi_ext_rfence,
>  	&vcpu_sbi_ext_srst,
>  	&vcpu_sbi_ext_hsm,
> +	&vcpu_sbi_ext_pmu,
>  	&vcpu_sbi_ext_experimental,
>  	&vcpu_sbi_ext_vendor,
>  };
> diff --git a/arch/riscv/kvm/vcpu_sbi_pmu.c b/arch/riscv/kvm/vcpu_sbi_pmu.c
> new file mode 100644
> index 0000000..223752f
> --- /dev/null
> +++ b/arch/riscv/kvm/vcpu_sbi_pmu.c
> @@ -0,0 +1,86 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2022 Rivos Inc
> + *
> + * Authors:
> + *     Atish Patra <atishp@xxxxxxxxxxxx>
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/err.h>
> +#include <linux/kvm_host.h>
> +#include <asm/csr.h>
> +#include <asm/sbi.h>
> +#include <asm/kvm_vcpu_sbi.h>
> +
> +static int kvm_sbi_ext_pmu_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
> +				   struct kvm_vcpu_sbi_ext_data *edata,
> +				   struct kvm_cpu_trap *utrap)
> +{
> +	int ret = 0;
> +	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
> +	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> +	unsigned long funcid = cp->a6;
> +	uint64_t temp;
> +
> +	/* Return not supported if PMU is not initialized */
> +	if (!kvpmu->init_done)
> +		return -EINVAL;
> +
> +	switch (funcid) {
> +	case SBI_EXT_PMU_NUM_COUNTERS:
> +		ret = kvm_riscv_vcpu_pmu_num_ctrs(vcpu, edata);
> +		break;
> +	case SBI_EXT_PMU_COUNTER_GET_INFO:
> +		ret = kvm_riscv_vcpu_pmu_ctr_info(vcpu, cp->a0, edata);
> +		break;
> +	case SBI_EXT_PMU_COUNTER_CFG_MATCH:
> +#if defined(CONFIG_32BIT)
> +		temp = ((uint64_t)cp->a5 << 32) | cp->a4;
> +#else
> +		temp = cp->a4;
> +#endif
> +		ret = kvm_riscv_vcpu_pmu_ctr_cfg_match(vcpu, cp->a0, cp->a1,
> +						       cp->a2, cp->a3, temp, edata);
> +		break;
> +	case SBI_EXT_PMU_COUNTER_START:
> +#if defined(CONFIG_32BIT)
> +		temp = ((uint64_t)cp->a4 << 32) | cp->a3;
> +#else
> +		temp = cp->a3;
> +#endif
> +		ret = kvm_riscv_vcpu_pmu_ctr_start(vcpu, cp->a0, cp->a1, cp->a2,
> +						   temp, edata);
> +		break;
> +	case SBI_EXT_PMU_COUNTER_STOP:
> +		ret = kvm_riscv_vcpu_pmu_ctr_stop(vcpu, cp->a0, cp->a1, cp->a2, edata);
> +		break;
> +	case SBI_EXT_PMU_COUNTER_FW_READ:
> +		ret = kvm_riscv_vcpu_pmu_ctr_read(vcpu, cp->a0, edata);
> +		break;
> +	default:
> +		edata->err_val = SBI_ERR_NOT_SUPPORTED;
> +	}
> +
> +
> +	return ret;
> +}
> +
> +unsigned long kvm_sbi_ext_pmu_probe(struct kvm_vcpu *vcpu, unsigned long extid)
> +{
> +	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> +
> +	/*
> +	 * PMU Extension is only available to guests if privilege mode filtering
> +	 * is available. Otherwise, guest will always count events while the
> +	 * execution is in hypervisor mode.
> +	 */
> +	return kvpmu->init_done && riscv_isa_extension_available(NULL, SSCOFPMF);

Assuming we're only supporting homogeneous systems, then can't we just
check for Sscofpmf at PMU init time? When the extension isn't present
we'd fail to init and then here init_done wouldn't be set.

> +}
> +
> +const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pmu = {
> +	.extid_start = SBI_EXT_PMU,
> +	.extid_end = SBI_EXT_PMU,
> +	.handler = kvm_sbi_ext_pmu_handler,
> +	.probe = kvm_sbi_ext_pmu_probe,
> +};
> -- 
> 2.25.1
>

Thanks,
drew