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 <CAAhSdy1P=u4a-4t8kn2Pa3Zs+Njai36QV9hBrwYk8zkhdR8r5g@mail.gmail.com>
In-Reply-To: <CAAhSdy1P=u4a-4t8kn2Pa3Zs+Njai36QV9hBrwYk8zkhdR8r5g@mail.gmail.com>
From:   Atish Patra <atishp@atishpatra.org>
Date:   Tue, 31 Jan 2023 14:35:13 -0800
Message-ID: <CAOnJCUK+Ht10utv=18jET=sUTR5660Sm5Tf+e0zyQjUJ9m10_Q@mail.gmail.com>
Subject: Re: [PATCH v3 07/14] RISC-V: KVM: Add skeleton support for perf
To:     Anup Patel <anup@brainfault.org>
Cc:     Atish Patra <atishp@rivosinc.com>, linux-kernel@vger.kernel.org,
        Andrew Jones <ajones@ventanamicro.com>,
        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 Sun, Jan 29, 2023 at 4:30 AM Anup Patel <anup@brainfault.org> wrote:
>
> On Fri, Jan 27, 2023 at 11:56 PM Atish Patra <atishp@rivosinc.com> wrote:
> >
> > This patch only adds barebore structure of perf implementation. Most of
>
> s/barebore/barebone/
>
> > the function returns zero at this point and will be implemented
> > fully in the future.
> >
> > Signed-off-by: Atish Patra <atishp@rivosinc.com>
> > ---
> >  arch/riscv/include/asm/kvm_host.h     |   3 +
> >  arch/riscv/include/asm/kvm_vcpu_pmu.h |  76 ++++++++++++++
> >  arch/riscv/kvm/Makefile               |   1 +
> >  arch/riscv/kvm/vcpu.c                 |   5 +
> >  arch/riscv/kvm/vcpu_pmu.c             | 145 ++++++++++++++++++++++++++
> >  5 files changed, 230 insertions(+)
> >  create mode 100644 arch/riscv/include/asm/kvm_vcpu_pmu.h
> >  create mode 100644 arch/riscv/kvm/vcpu_pmu.c
> >
> > diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> > index 93f43a3..f9874b4 100644
> > --- a/arch/riscv/include/asm/kvm_host.h
> > +++ b/arch/riscv/include/asm/kvm_host.h
> > @@ -18,6 +18,7 @@
> >  #include <asm/kvm_vcpu_insn.h>
> >  #include <asm/kvm_vcpu_sbi.h>
> >  #include <asm/kvm_vcpu_timer.h>
> > +#include <asm/kvm_vcpu_pmu.h>
> >
> >  #define KVM_MAX_VCPUS                  1024
> >
> > @@ -228,6 +229,8 @@ struct kvm_vcpu_arch {
> >
> >         /* Don't run the VCPU (blocked) */
> >         bool pause;
> > +
> > +       struct kvm_pmu pmu;
>
> Add a single line comment just like other members of the structure.
>
> I also suggest naming this variable "pmu_context" or something similar
> for naming consistency.
>

Done.

> >  };
> >
> >  static inline void kvm_arch_hardware_unsetup(void) {}
> > diff --git a/arch/riscv/include/asm/kvm_vcpu_pmu.h b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> > new file mode 100644
> > index 0000000..3f43a43
> > --- /dev/null
> > +++ b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> > @@ -0,0 +1,76 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Copyright (c) 2023 Rivos Inc
> > + *
> > + * Authors:
> > + *     Atish Patra <atishp@rivosinc.com>
> > + */
> > +
> > +#ifndef __KVM_VCPU_RISCV_PMU_H
> > +#define __KVM_VCPU_RISCV_PMU_H
> > +
> > +#include <linux/perf/riscv_pmu.h>
> > +#include <asm/kvm_vcpu_sbi.h>
> > +#include <asm/sbi.h>
> > +
> > +#ifdef CONFIG_RISCV_PMU_SBI
> > +#define RISCV_KVM_MAX_FW_CTRS 32
> > +#define RISCV_MAX_COUNTERS      64
> > +
> > +/* Per virtual pmu counter data */
> > +struct kvm_pmc {
> > +       u8 idx;
> > +       struct perf_event *perf_event;
> > +       uint64_t counter_val;
> > +       union sbi_pmu_ctr_info cinfo;
> > +       /* Event monitoring status */
> > +       bool started;
> > +};
> > +
> > +/* PMU data structure per vcpu */
> > +struct kvm_pmu {
> > +       struct kvm_pmc pmc[RISCV_MAX_COUNTERS];
> > +       /* Number of the virtual firmware counters available */
> > +       int num_fw_ctrs;
> > +       /* Number of the virtual hardware counters available */
> > +       int num_hw_ctrs;
> > +       /* A flag to indicate that pmu initialization is done */
> > +       bool init_done;
> > +       /* Bit map of all the virtual counter used */
> > +       DECLARE_BITMAP(pmc_in_use, RISCV_MAX_COUNTERS);
> > +};
> > +
> > +#define vcpu_to_pmu(vcpu) (&(vcpu)->arch.pmu)
> > +#define pmu_to_vcpu(pmu)  (container_of((pmu), struct kvm_vcpu, arch.pmu))
> > +
> > +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);
> > +int kvm_riscv_vcpu_pmu_ctr_start(struct kvm_vcpu *vcpu, unsigned long ctr_base,
> > +                                unsigned long ctr_mask, unsigned long flag, uint64_t ival,
> > +                                struct kvm_vcpu_sbi_ext_data *edata);
> > +int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
> > +                               unsigned long ctr_mask, unsigned long flag,
> > +                               struct kvm_vcpu_sbi_ext_data *edata);
> > +int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_base,
> > +                                    unsigned long ctr_mask, unsigned long flag,
> > +                                    unsigned long eidx, uint64_t evtdata,
> > +                                    struct kvm_vcpu_sbi_ext_data *edata);
> > +int kvm_riscv_vcpu_pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
> > +                               struct kvm_vcpu_sbi_ext_data *edata);
> > +int kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu);
> > +void kvm_riscv_vcpu_pmu_deinit(struct kvm_vcpu *vcpu);
> > +void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu);
> > +
> > +#else
> > +struct kvm_pmu {
> > +};
> > +
> > +static inline int kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu)
> > +{
> > +       return 0;
> > +}
> > +static inline void kvm_riscv_vcpu_pmu_deinit(struct kvm_vcpu *vcpu) {}
> > +static inline void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu) {}
> > +#endif /* CONFIG_RISCV_PMU_SBI */
> > +#endif /* !__KVM_VCPU_RISCV_PMU_H */
> > diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
> > index 019df920..5de1053 100644
> > --- a/arch/riscv/kvm/Makefile
> > +++ b/arch/riscv/kvm/Makefile
> > @@ -25,3 +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
> > diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> > index 7c08567..b746f21 100644
> > --- a/arch/riscv/kvm/vcpu.c
> > +++ b/arch/riscv/kvm/vcpu.c
> > @@ -137,6 +137,7 @@ static void kvm_riscv_reset_vcpu(struct kvm_vcpu *vcpu)
> >
> >         WRITE_ONCE(vcpu->arch.irqs_pending, 0);
> >         WRITE_ONCE(vcpu->arch.irqs_pending_mask, 0);
>
> Add an empty newline here.
>

Done.
> > +       kvm_riscv_vcpu_pmu_reset(vcpu);
> >
> >         vcpu->arch.hfence_head = 0;
> >         vcpu->arch.hfence_tail = 0;
> > @@ -194,6 +195,9 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> >         /* Setup VCPU timer */
> >         kvm_riscv_vcpu_timer_init(vcpu);
> >
> > +       /* setup performance monitoring */
> > +       kvm_riscv_vcpu_pmu_init(vcpu);
> > +
> >         /* Reset VCPU */
> >         kvm_riscv_reset_vcpu(vcpu);
> >
> > @@ -216,6 +220,7 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
> >         /* Cleanup VCPU timer */
> >         kvm_riscv_vcpu_timer_deinit(vcpu);
> >
> > +       kvm_riscv_vcpu_pmu_deinit(vcpu);
>
> Add an empty newline here.
>

Done.

> >         /* Free unused pages pre-allocated for G-stage page table mappings */
> >         kvm_mmu_free_memory_cache(&vcpu->arch.mmu_page_cache);
> >  }
> > diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> > new file mode 100644
> > index 0000000..d3fd551
> > --- /dev/null
> > +++ b/arch/riscv/kvm/vcpu_pmu.c
> > @@ -0,0 +1,145 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (c) 2023 Rivos Inc
> > + *
> > + * Authors:
> > + *     Atish Patra <atishp@rivosinc.com>
> > + */
> > +
> > +#include <linux/errno.h>
> > +#include <linux/err.h>
> > +#include <linux/kvm_host.h>
> > +#include <linux/perf/riscv_pmu.h>
> > +#include <asm/csr.h>
> > +#include <asm/kvm_vcpu_sbi.h>
> > +#include <asm/kvm_vcpu_pmu.h>
> > +#include <linux/kvm_host.h>
> > +
> > +#define kvm_pmu_num_counters(pmu) ((pmu)->num_hw_ctrs + (pmu)->num_fw_ctrs)
> > +
> > +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);
> > +
> > +       edata->out_val = kvm_pmu_num_counters(kvpmu);
> > +
> > +       return 0;
> > +}
> > +
> > +int kvm_riscv_vcpu_pmu_ctr_info(struct kvm_vcpu *vcpu, unsigned long cidx,
> > +                               struct kvm_vcpu_sbi_ext_data *edata)
> > +{
> > +       struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> > +
> > +       if (cidx > RISCV_MAX_COUNTERS || cidx == 1) {
> > +               edata->err_val = SBI_ERR_INVALID_PARAM;
> > +               return 0;
> > +       }
> > +
> > +       edata->out_val = kvpmu->pmc[cidx].cinfo.value;
> > +
> > +       return 0;
> > +}
> > +
> > +int kvm_riscv_vcpu_pmu_ctr_start(struct kvm_vcpu *vcpu, unsigned long ctr_base,
> > +                                unsigned long ctr_mask, unsigned long flag, uint64_t ival,
> > +                                struct kvm_vcpu_sbi_ext_data *edata)
> > +{
> > +       /* TODO */
> > +       return 0;
> > +}
> > +
> > +int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
> > +                               unsigned long ctr_mask, unsigned long flag,
> > +                               struct kvm_vcpu_sbi_ext_data *edata)
> > +{
> > +       /* TODO */
> > +       return 0;
> > +}
> > +
> > +int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_base,
> > +                                    unsigned long ctr_mask, unsigned long flag,
> > +                                    unsigned long eidx, uint64_t evtdata,
> > +                                    struct kvm_vcpu_sbi_ext_data *edata)
> > +{
> > +       /* TODO */
> > +       return 0;
> > +}
> > +
> > +int kvm_riscv_vcpu_pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
> > +                               struct kvm_vcpu_sbi_ext_data *edata)
> > +{
> > +       /* TODO */
> > +       return 0;
> > +}
> > +
> > +int kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu)
> > +{
> > +       int i = 0, num_fw_ctrs, ret, num_hw_ctrs = 0, hpm_width = 0;
> > +       struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> > +       struct kvm_pmc *pmc;
> > +
> > +       ret = riscv_pmu_get_hpm_info(&hpm_width, &num_hw_ctrs);
> > +       if (ret < 0)
> > +               return ret;
> > +
> > +       if (!hpm_width || !num_hw_ctrs) {
> > +               pr_err("Cannot initialize VCPU with NULL hpmcounter width or number of counters\n");
>
> What will happen if underlying M-mode firmware does not implement
> SBI PMU extension ?
>

riscv_pmu_get_hpm_info will return an error and
kvm_riscv_vcpu_pmu_init will fail.

> > +               return -EINVAL;
> > +       }
> > +
> > +       if ((num_hw_ctrs + RISCV_KVM_MAX_FW_CTRS) > RISCV_MAX_COUNTERS) {
> > +               pr_warn("Limiting fw counters as hw & fw counters exceed maximum counters\n");
>
> How is this possible ?
>
> Maximum HW counters is 32 (including time, cycle, and instret),
> RISCV_KVM_MAX_FW_CTRS = 32, and
> RISCV_MAX_COUNTERS = 64

This was added to prevent the condition where somebody changed the
definition RISCV_KVM_MAX_FW_CTRS
without incrementing MAX_COUNTERS. The error might be subtle as it may
work on some platforms (with less hardware counter)
but fail on others (with more hardware counters.)
I couldn't find a better way to describe the relationship between
RISCV_KVM_MAX_FW_CTRS and RISCV_MAX_COUNTERS.

I can just put a big comment here instead of the condition check if
you prefer that way.


>
> > +               num_fw_ctrs = RISCV_MAX_COUNTERS - num_hw_ctrs;
> > +       } else
> > +               num_fw_ctrs = RISCV_KVM_MAX_FW_CTRS;
> > +
> > +       kvpmu->num_hw_ctrs = num_hw_ctrs;
> > +       kvpmu->num_fw_ctrs = num_fw_ctrs;
> > +
> > +       /*
> > +        * There is no correlation between the logical hardware counter and virtual counters.
> > +        * However, we need to encode a hpmcounter CSR in the counter info field so that
> > +        * KVM can trap n emulate the read. This works well in the migration use case as
> > +        * KVM doesn't care if the actual hpmcounter is available in the hardware or not.
> > +        */
> > +       for (i = 0; i < kvm_pmu_num_counters(kvpmu); i++) {
> > +               /* TIME CSR shouldn't be read from perf interface */
> > +               if (i == 1)
> > +                       continue;
> > +               pmc = &kvpmu->pmc[i];
> > +               pmc->idx = i;
> > +               if (i < kvpmu->num_hw_ctrs) {
> > +                       kvpmu->pmc[i].cinfo.type = SBI_PMU_CTR_TYPE_HW;
> > +                       if (i < 3)
> > +                               /* CY, IR counters */
> > +                               kvpmu->pmc[i].cinfo.width = 63;
> > +                       else
> > +                               kvpmu->pmc[i].cinfo.width = hpm_width;
> > +                       /*
> > +                        * The CSR number doesn't have any relation with the logical
> > +                        * hardware counters. The CSR numbers are encoded sequentially
> > +                        * to avoid maintaining a map between the virtual counter
> > +                        * and CSR number.
> > +                        */
> > +                       pmc->cinfo.csr = CSR_CYCLE + i;
> > +               } else {
> > +                       pmc->cinfo.type = SBI_PMU_CTR_TYPE_FW;
> > +                       pmc->cinfo.width = BITS_PER_LONG - 1;
> > +               }
> > +       }
> > +
> > +       kvpmu->init_done = true;
> > +
> > +       return 0;
> > +}
> > +
> > +void kvm_riscv_vcpu_pmu_deinit(struct kvm_vcpu *vcpu)
> > +{
> > +       /* TODO */
> > +}
> > +
> > +void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu)
> > +{
> > +       kvm_riscv_vcpu_pmu_deinit(vcpu);
> > +}
> > --
> > 2.25.1
> >
>
> Regards,
> Anup


-- 
Regards,
Atish