Re: [RFC 6/9] RISC-V: KVM: Add SBI PMU extension support

Andrew Jones
2022-11-01T14:26:47Z

On Mon, Jul 18, 2022 at 10:02:02AM -0700, 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@rivosinc.com>
> ---
> arch/riscv/kvm/vcpu_sbi.c | 11 +++++
> arch/riscv/kvm/vcpu_sbi_pmu.c | 81 +++++++++++++++++++++++++++++++++++
> 2 files changed, 92 insertions(+)
> create mode 100644 arch/riscv/kvm/vcpu_sbi_pmu.c
>
> diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
> index d45e7da3f0d3..da9f7959340e 100644
> --- a/arch/riscv/kvm/vcpu_sbi.c
> +++ b/arch/riscv/kvm/vcpu_sbi.c
> @@ -50,6 +50,16 @@ extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_hsm;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_experimental;
> extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_vendor;
>
> +#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,
> @@ -58,6 +68,7 @@ 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 000000000000..90c51a95d4f4
> --- /dev/null
> +++ b/arch/riscv/kvm/vcpu_sbi_pmu.c
> @@ -0,0 +1,81 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2022 Rivos Inc
> + *
> + * Authors:
> + * Atish Patra <atishp@rivosinc.com>
> + */
> +
> +#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,
> + unsigned long *out_val,
> + struct kvm_cpu_trap *utrap,
> + bool *exit)
> +{
> + int ret = -EOPNOTSUPP;
> + struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
> + unsigned long funcid = cp->a6;
> + uint64_t temp;

I think we need something like

if (!vcpu_to_pmu(vcpu)->enabled)
return -EOPNOTSUPP;

here. Where 'enabled' is only true when we successfully initialize
the pmu. And, successful initialization depends on
IS_ENABLED(CONFIG_RISCV_PMU_SBI) and
riscv_isa_extension_available(NULL, SSCOFPMF) as well as not
failing other things. And, KVM userspace should be able to
disable the pmu, which keep enabled from being set as well.

> +
> + switch (funcid) {
> + case SBI_EXT_PMU_NUM_COUNTERS:
> + ret = kvm_riscv_vcpu_pmu_num_ctrs(vcpu, out_val);
> + break;
> + case SBI_EXT_PMU_COUNTER_GET_INFO:
> + ret = kvm_riscv_vcpu_pmu_ctr_info(vcpu, cp->a0, out_val);
> + 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);
> + if (ret >= 0) {
> + *out_val = ret;
> + ret = 0;
> + }
> + 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);
> + break;
> + case SBI_EXT_PMU_COUNTER_STOP:
> + ret = kvm_riscv_vcpu_pmu_ctr_stop(vcpu, cp->a0, cp->a1, cp->a2);
> + break;
> + case SBI_EXT_PMU_COUNTER_FW_READ:
> + ret = kvm_riscv_vcpu_pmu_ctr_read(vcpu, cp->a0, out_val);
> + break;
> + default:
> + ret = -EOPNOTSUPP;
> + }
> +
> + return ret;
> +}
> +
> +unsigned long kvm_sbi_ext_pmu_probe(unsigned long extid)
> +{
> + /*
> + * 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 riscv_isa_extension_available(NULL, SSCOFPMF);
> +}
> +
> +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