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In-Reply-To: <CAK9=C2X11WuN4rr+7fesn-mP8dp-thX0gLWCNn3eObWUUYfoEA@mail.gmail.com>
From:   Atish Patra <atishp@atishpatra.org>
Date:   Wed, 1 Feb 2023 00:41:38 -0800
Message-ID: <CAOnJCUJC61n0W-smZLMiMaNv8qZ1hKBxxAQCvEQkQ0a7FHWj6w@mail.gmail.com>
Subject: Re: [PATCH v3 07/14] RISC-V: KVM: Add skeleton support for perf
To:     Anup Patel <apatel@ventanamicro.com>
Cc:     Anup Patel <anup@brainfault.org>,
        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>
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Precedence: bulk

On Tue, Jan 31, 2023 at 7:48 PM Anup Patel <apatel@ventanamicro.com> wrote:
>
> On Wed, Feb 1, 2023 at 4:05 AM Atish Patra <atishp@atishpatra.org> wrote:
> >
> > 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.
>
> Ahh okay. The vcpu_create() is not looking at return value
> of kvm_riscv_vcpu_pmu_init() but this function should fail
> silently "return 0" if riscv_pmu_get_hpm_info() fails.
>

Sure. I am assuming it should return 0 for the next case as well.
if (!hpm_width || !num_hw_ctrs)

Thinking over again, does it make sense to print the error message in
the above case ?
In case you do see some use of this error message, it probably needs
improvement as well

"Cannot initialize pmu for vcpu %d with invalid counter width or
number of counters"

> >
> > > > +               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.
>
> Maybe you can add a compile-time check using "#if" and "#error" ?
>

You mean compile time error when RISCV_KVM_MAX_FW_CTRS > 32 ?
Because num_hw_ctrs is computed at the runtime. So we can't determine
the actual limit of firmware counters unless we know how many hardware
counters are there.

> >
> >
> > >
> > > > +               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
>
> Regards,
> Anup


-- 
Regards,
Atish