MIME-Version: 1.0
References: <20230127182558.2416400-1-atishp@rivosinc.com> <20230127182558.2416400-12-atishp@rivosinc.com>
In-Reply-To: <20230127182558.2416400-12-atishp@rivosinc.com>
From:   Anup Patel <anup@brainfault.org>
Date:   Sun, 29 Jan 2023 18:14:18 +0530
Message-ID: <CAAhSdy1+6AprOdzRRTG98p6swisNFO6MUKjXobxW3RWbixvjCg@mail.gmail.com>
Subject: Re: [PATCH v3 11/14] RISC-V: KVM: Implement trap & emulate for hpmcounters
To:     Atish Patra <atishp@rivosinc.com>
Cc:     linux-kernel@vger.kernel.org,
        Andrew Jones <ajones@ventanamicro.com>,
        Atish Patra <atishp@atishpatra.org>,
        Guo Ren <guoren@kernel.org>, Heiko Stuebner <heiko@sntech.de>,
        kvm-riscv@lists.infradead.org, kvm@vger.kernel.org,
        linux-riscv@lists.infradead.org,
        Mark Rutland <mark.rutland@arm.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Sergey Matyukevich <sergey.matyukevich@syntacore.com>,
        Will Deacon <will@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Jan 27, 2023 at 11:56 PM Atish Patra <atishp@rivosinc.com> wrote:
>
> As the KVM guests only see the virtual PMU counters, all hpmcounter
> access should trap and KVM emulates the read access on behalf of guests.
>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
> ---
>  arch/riscv/include/asm/kvm_vcpu_pmu.h | 16 ++++++++++
>  arch/riscv/kvm/vcpu_insn.c            |  4 ++-
>  arch/riscv/kvm/vcpu_pmu.c             | 45 ++++++++++++++++++++++++++-
>  3 files changed, 63 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/asm/kvm_vcpu_pmu.h b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> index 3f43a43..022d45d 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_pmu.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> @@ -43,6 +43,19 @@ struct kvm_pmu {
>  #define vcpu_to_pmu(vcpu) (&(vcpu)->arch.pmu)
>  #define pmu_to_vcpu(pmu)  (container_of((pmu), struct kvm_vcpu, arch.pmu))
>
> +#if defined(CONFIG_32BIT)
> +#define KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS \
> +{ .base = CSR_CYCLEH,      .count = 31, .func = kvm_riscv_vcpu_pmu_read_hpm }, \
> +{ .base = CSR_CYCLE,      .count = 31, .func = kvm_riscv_vcpu_pmu_read_hpm },
> +#else
> +#define KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS \
> +{ .base = CSR_CYCLE,      .count = 31, .func = kvm_riscv_vcpu_pmu_read_hpm },
> +#endif
> +
> +int kvm_riscv_vcpu_pmu_read_hpm(struct kvm_vcpu *vcpu, unsigned int csr_num,
> +                               unsigned long *val, unsigned long new_val,
> +                               unsigned long wr_mask);
> +
>  int kvm_riscv_vcpu_pmu_num_ctrs(struct kvm_vcpu *vcpu, struct kvm_vcpu_sbi_ext_data *edata);
>  int kvm_riscv_vcpu_pmu_ctr_info(struct kvm_vcpu *vcpu, unsigned long cidx,
>                                 struct kvm_vcpu_sbi_ext_data *edata);
> @@ -65,6 +78,9 @@ void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu);
>  #else
>  struct kvm_pmu {
>  };
> +#define KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS \
> +{ .base = 0,      .count = 0, .func = NULL },
> +

Redundant newline here.

>
>  static inline int kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu)
>  {
> diff --git a/arch/riscv/kvm/vcpu_insn.c b/arch/riscv/kvm/vcpu_insn.c
> index 0bb5276..f689337 100644
> --- a/arch/riscv/kvm/vcpu_insn.c
> +++ b/arch/riscv/kvm/vcpu_insn.c
> @@ -213,7 +213,9 @@ struct csr_func {
>                     unsigned long wr_mask);
>  };
>
> -static const struct csr_func csr_funcs[] = { };
> +static const struct csr_func csr_funcs[] = {
> +       KVM_RISCV_VCPU_HPMCOUNTER_CSR_FUNCS
> +};
>
>  /**
>   * kvm_riscv_vcpu_csr_return -- Handle CSR read/write after user space
> diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> index 7713927..894053a 100644
> --- a/arch/riscv/kvm/vcpu_pmu.c
> +++ b/arch/riscv/kvm/vcpu_pmu.c
> @@ -17,6 +17,44 @@
>
>  #define kvm_pmu_num_counters(pmu) ((pmu)->num_hw_ctrs + (pmu)->num_fw_ctrs)
>
> +static int pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
> +                       unsigned long *out_val)
> +{
> +       struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> +       struct kvm_pmc *pmc;
> +       u64 enabled, running;
> +
> +       pmc = &kvpmu->pmc[cidx];
> +       if (!pmc->perf_event)
> +               return -EINVAL;
> +
> +       pmc->counter_val += perf_event_read_value(pmc->perf_event, &enabled, &running);
> +       *out_val = pmc->counter_val;
> +
> +       return 0;
> +}
> +
> +int kvm_riscv_vcpu_pmu_read_hpm(struct kvm_vcpu *vcpu, unsigned int csr_num,
> +                               unsigned long *val, unsigned long new_val,
> +                               unsigned long wr_mask)
> +{
> +       struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> +       int cidx, ret = KVM_INSN_CONTINUE_NEXT_SEPC;
> +
> +       if (!kvpmu || !kvpmu->init_done)
> +               return KVM_INSN_EXIT_TO_USER_SPACE;

As discussed previously, this should be KVM_INSN_ILLEGAL_TRAP.

> +
> +       if (wr_mask)
> +               return KVM_INSN_ILLEGAL_TRAP;
> +
> +       cidx = csr_num - CSR_CYCLE;
> +
> +       if (pmu_ctr_read(vcpu, cidx, val) < 0)
> +               return KVM_INSN_EXIT_TO_USER_SPACE;

Same as above.

> +
> +       return ret;
> +}
> +
>  int kvm_riscv_vcpu_pmu_num_ctrs(struct kvm_vcpu *vcpu, struct kvm_vcpu_sbi_ext_data *edata)
>  {
>         struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> @@ -69,7 +107,12 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
>  int kvm_riscv_vcpu_pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
>                                 struct kvm_vcpu_sbi_ext_data *edata)
>  {
> -       /* TODO */
> +       int ret;
> +
> +       ret = pmu_ctr_read(vcpu, cidx, &edata->out_val);
> +       if (ret == -EINVAL)
> +               edata->err_val = SBI_ERR_INVALID_PARAM;
> +
>         return 0;
>  }
>
> --
> 2.25.1
>

Regards,
Anup