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References: <20220718170205.2972215-1-atishp@rivosinc.com> <20220718170205.2972215-9-atishp@rivosinc.com>
In-Reply-To: <20220718170205.2972215-9-atishp@rivosinc.com>
From:   Eric Lin <eric.lin@sifive.com>
Date:   Tue, 20 Sep 2022 10:24:34 +0800
Message-ID: <CAPqJEFp2NamR0hOA1HGAW7aPtn2OYw0N8ir=xQQ3AdEJU15dtQ@mail.gmail.com>
Subject: Re: [RFC 8/9] RISC-V: KVM: Implement perf support
To:     Atish Patra <atishp@rivosinc.com>
Cc:     linux-kernel@vger.kernel.org, Albert Ou <aou@eecs.berkeley.edu>,
        Anup Patel <anup@brainfault.org>,
        Atish Patra <atishp@atishpatra.org>,
        Guo Ren <guoren@kernel.org>, 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>,
        Will Deacon <will@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi Atish,

On Tue, Jul 19, 2022 at 2:01 AM Atish Patra <atishp@rivosinc.com> wrote:
>
> RISC-V SBI PMU & Sscofpmf ISA extension allows supporting perf in
> the virtualization enviornment as well. KVM implementation
> relies on SBI PMU extension for most of the part while traps
> & emulates the CSRs read for counter access.
>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
> ---
>  arch/riscv/kvm/vcpu_pmu.c | 318 ++++++++++++++++++++++++++++++++++++--
>  1 file changed, 301 insertions(+), 17 deletions(-)
>
> diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> index 5434051f495d..278c261efad3 100644
> --- a/arch/riscv/kvm/vcpu_pmu.c
> +++ b/arch/riscv/kvm/vcpu_pmu.c
> @@ -11,9 +11,163 @@
>  #include <linux/kvm_host.h>
>  #include <linux/perf/riscv_pmu.h>
>  #include <asm/csr.h>
> +#include <asm/bitops.h>
>  #include <asm/kvm_vcpu_pmu.h>
>  #include <linux/kvm_host.h>
>
> +#define get_event_type(x) ((x & SBI_PMU_EVENT_IDX_TYPE_MASK) >> 16)
> +#define get_event_code(x) (x & SBI_PMU_EVENT_IDX_CODE_MASK)
> +
> +static inline u64 pmu_get_sample_period(struct kvm_pmc *pmc)
> +{
> +       u64 counter_val_mask = GENMASK(pmc->cinfo.width, 0);
> +       u64 sample_period;
> +
> +       if (!pmc->counter_val)
> +               sample_period = counter_val_mask;
> +       else
> +               sample_period = pmc->counter_val & counter_val_mask;

I think sample_period should be =>
sample_period = (-pmc->counter_val) & counter_val_mask

When we are doing event counting, the pmu counter initial value comes
from the guest kernel is 0x800000000000000X.
If we let the sample period be the (pmc->counter_val) &
counter_val_mask, the sample_period will be 0x800000000000000X.
After we pass this sample_period to the host pmu driver, in
riscv_pmu_event_set_period(), it will make the final pmu counter
initial value be 0xffffffffffXX.
This will make the pmu counter overflow interrupt frequently and
trigger soft lockup in kvm guest.

I also checked the arm64 kvm perf implementation as below, its
sample_period is attr.sample_period = (-counter) & GENMASK(63, 0)

 624 static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64
select_idx)
 625 {
....
 688                 /* The initial sample period (overflow count) of
an event. */
 689                 if (kvm_pmu_idx_is_64bit(vcpu, pmc->idx))
 690                         attr.sample_period = (-counter) & GENMASK(63, 0);
 691                 else
 692                         attr.sample_period = (-counter) & GENMASK(31, 0);

After I apply the patch as below, no occur counter overflow interrupt
and the pmu counter initial value is the same as we do event counting
in the host.

--- a/arch/riscv/kvm/vcpu_pmu.c
+++ b/arch/riscv/kvm/vcpu_pmu.c
@@ -26,7 +26,7 @@ static inline u64 pmu_get_sample_period(struct kvm_pmc *pmc)
        if (!pmc->counter_val)
                sample_period = counter_val_mask;
        else
-               sample_period = pmc->counter_val & counter_val_mask;
+               sample_period = (-pmc->counter_val) & counter_val_mask;

Thanks,
Eric Lin

> +
> +       return sample_period;
> +}
> +
> +static u32 pmu_get_perf_event_type(unsigned long eidx)
> +{
> +       enum sbi_pmu_event_type etype = get_event_type(eidx);
> +       u32 type;
> +
> +       if (etype == SBI_PMU_EVENT_TYPE_HW)
> +               type = PERF_TYPE_HARDWARE;
> +       else if (etype == SBI_PMU_EVENT_TYPE_CACHE)
> +               type = PERF_TYPE_HW_CACHE;
> +       else if (etype == SBI_PMU_EVENT_TYPE_RAW || etype == SBI_PMU_EVENT_TYPE_FW)
> +               type = PERF_TYPE_RAW;
> +       else
> +               type = PERF_TYPE_MAX;
> +
> +       return type;
> +}
> +
> +static inline bool pmu_is_fw_event(unsigned long eidx)
> +{
> +       enum sbi_pmu_event_type etype = get_event_type(eidx);
> +
> +       return (etype == SBI_PMU_EVENT_TYPE_FW) ? true : false;
> +}
> +
> +static void pmu_release_perf_event(struct kvm_pmc *pmc)
> +{
> +       if (pmc->perf_event) {
> +               perf_event_disable(pmc->perf_event);
> +               perf_event_release_kernel(pmc->perf_event);
> +               pmc->perf_event = NULL;
> +       }
> +}
> +
> +static u64 pmu_get_perf_event_hw_config(u32 sbi_event_code)
> +{
> +       /* SBI PMU HW event code is offset by 1 from perf hw event codes */
> +       return (u64)sbi_event_code - 1;
> +}
> +
> +static u64 pmu_get_perf_event_cache_config(u32 sbi_event_code)
> +{
> +       u64 config = U64_MAX;
> +       unsigned int cache_type, cache_op, cache_result;
> +
> +       /* All the cache event masks lie within 0xFF. No separate masking is necesssary */
> +       cache_type = (sbi_event_code & SBI_PMU_EVENT_CACHE_ID_CODE_MASK) >> 3;
> +       cache_op = (sbi_event_code & SBI_PMU_EVENT_CACHE_OP_ID_CODE_MASK) >> 1;
> +       cache_result = sbi_event_code & SBI_PMU_EVENT_CACHE_RESULT_ID_CODE_MASK;
> +
> +       if (cache_type >= PERF_COUNT_HW_CACHE_MAX ||
> +           cache_op >= PERF_COUNT_HW_CACHE_OP_MAX ||
> +           cache_result >= PERF_COUNT_HW_CACHE_RESULT_MAX)
> +               goto out;
> +       config = cache_type | (cache_op << 8) | (cache_result << 16);
> +out:
> +       return config;
> +}
> +
> +static u64 pmu_get_perf_event_config(unsigned long eidx, uint64_t edata)
> +{
> +       enum sbi_pmu_event_type etype = get_event_type(eidx);
> +       u32 ecode = get_event_code(eidx);
> +       u64 config = U64_MAX;
> +
> +       if (etype == SBI_PMU_EVENT_TYPE_HW)
> +               config = pmu_get_perf_event_hw_config(ecode);
> +       else if (etype == SBI_PMU_EVENT_TYPE_CACHE)
> +               config = pmu_get_perf_event_cache_config(ecode);
> +       else if (etype == SBI_PMU_EVENT_TYPE_RAW)
> +               config = edata & RISCV_PMU_RAW_EVENT_MASK;
> +       else if ((etype == SBI_PMU_EVENT_TYPE_FW) && (ecode < SBI_PMU_FW_MAX))
> +               config = (1ULL << 63) | ecode;
> +
> +       return config;
> +}
> +
> +static int pmu_get_fixed_pmc_index(unsigned long eidx)
> +{
> +       u32 etype = pmu_get_perf_event_type(eidx);
> +       u32 ecode = get_event_code(eidx);
> +       int ctr_idx;
> +
> +       if (etype != SBI_PMU_EVENT_TYPE_HW)
> +               return -EINVAL;
> +
> +       if (ecode == SBI_PMU_HW_CPU_CYCLES)
> +               ctr_idx = 0;
> +       else if (ecode == SBI_PMU_HW_INSTRUCTIONS)
> +               ctr_idx = 2;
> +       else
> +               return -EINVAL;
> +
> +       return ctr_idx;
> +}
> +
> +static int pmu_get_programmable_pmc_index(struct kvm_pmu *kvpmu, unsigned long eidx,
> +                                         unsigned long cbase, unsigned long cmask)
> +{
> +       int ctr_idx = -1;
> +       int i, pmc_idx;
> +       int min, max;
> +
> +       if (pmu_is_fw_event(eidx)) {
> +               /* Firmware counters are mapped 1:1 starting from num_hw_ctrs for simplicity */
> +               min = kvpmu->num_hw_ctrs;
> +               max = min + kvpmu->num_fw_ctrs;
> +       } else {
> +               /* First 3 counters are reserved for fixed counters */
> +               min = 3;
> +               max = kvpmu->num_hw_ctrs;
> +       }
> +
> +       for_each_set_bit(i, &cmask, BITS_PER_LONG) {
> +               pmc_idx = i + cbase;
> +               if ((pmc_idx >= min && pmc_idx < max) &&
> +                   !test_bit(pmc_idx, kvpmu->used_pmc)) {
> +                       ctr_idx = pmc_idx;
> +                       break;
> +               }
> +       }
> +
> +       return ctr_idx;
> +}
> +
> +static int pmu_get_pmc_index(struct kvm_pmu *pmu, unsigned long eidx,
> +                            unsigned long cbase, unsigned long cmask)
> +{
> +       int ret;
> +
> +       /* Fixed counters need to be have fixed mapping as they have different width */
> +       ret = pmu_get_fixed_pmc_index(eidx);
> +       if (ret >= 0)
> +               return ret;
> +
> +       return pmu_get_programmable_pmc_index(pmu, eidx, cbase, cmask);
> +}
> +
>  int kvm_riscv_vcpu_pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
>                                 unsigned long *out_val)
>  {
> @@ -43,7 +197,6 @@ int kvm_riscv_vcpu_pmu_read_hpm(struct kvm_vcpu *vcpu, unsigned int csr_num,
>
>         if (!kvpmu)
>                 return KVM_INSN_EXIT_TO_USER_SPACE;
> -       //TODO: Should we check if vcpu pmu is initialized or not!
>         if (wr_mask)
>                 return KVM_INSN_ILLEGAL_TRAP;
>         cidx = csr_num - CSR_CYCLE;
> @@ -81,14 +234,62 @@ int kvm_riscv_vcpu_pmu_ctr_info(struct kvm_vcpu *vcpu, unsigned long cidx,
>  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)
>  {
> -       /* TODO */
> +       struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> +       int i, num_ctrs, pmc_index;
> +       struct kvm_pmc *pmc;
> +
> +       num_ctrs = kvpmu->num_fw_ctrs + kvpmu->num_hw_ctrs;
> +       if (ctr_base + __fls(ctr_mask) >= num_ctrs)
> +               return -EINVAL;
> +
> +       /* Start the counters that have been configured and requested by the guest */
> +       for_each_set_bit(i, &ctr_mask, RISCV_MAX_COUNTERS) {
> +               pmc_index = i + ctr_base;
> +               if (!test_bit(pmc_index, kvpmu->used_pmc))
> +                       continue;
> +               pmc = &kvpmu->pmc[pmc_index];
> +               if (flag & SBI_PMU_START_FLAG_SET_INIT_VALUE)
> +                       pmc->counter_val = ival;
> +               if (pmc->perf_event) {
> +                       perf_event_period(pmc->perf_event, pmu_get_sample_period(pmc));
> +                       perf_event_enable(pmc->perf_event);
> +               }
> +       }
> +
>         return 0;
>  }
>
>  int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
>                                  unsigned long ctr_mask, unsigned long flag)
>  {
> -       /* TODO */
> +       struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> +       int i, num_ctrs, pmc_index;
> +       u64 enabled, running;
> +       struct kvm_pmc *pmc;
> +
> +       num_ctrs = kvpmu->num_fw_ctrs + kvpmu->num_hw_ctrs;
> +       if ((ctr_base + __fls(ctr_mask)) >= num_ctrs)
> +               return -EINVAL;
> +
> +       /* Stop the counters that have been configured and requested by the guest */
> +       for_each_set_bit(i, &ctr_mask, RISCV_MAX_COUNTERS) {
> +               pmc_index = i + ctr_base;
> +               if (!test_bit(pmc_index, kvpmu->used_pmc))
> +                       continue;
> +               pmc = &kvpmu->pmc[pmc_index];
> +               if (pmc->perf_event) {
> +                       /* Stop counting the counter */
> +                       perf_event_disable(pmc->perf_event);
> +                       if (flag & SBI_PMU_STOP_FLAG_RESET) {
> +                               /* Relase the counter if this is a reset request */
> +                               pmc->counter_val += perf_event_read_value(pmc->perf_event,
> +                                                                         &enabled, &running);
> +                               pmu_release_perf_event(pmc);
> +                               clear_bit(pmc_index, kvpmu->used_pmc);
> +                       }
> +               }
> +       }
> +
>         return 0;
>  }
>
> @@ -96,14 +297,85 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
>                                      unsigned long ctr_mask, unsigned long flag,
>                                      unsigned long eidx, uint64_t edata)
>  {
> -       /* TODO */
> -       return 0;
> +       struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> +       struct perf_event *event;
> +       struct perf_event_attr attr;
> +       int num_ctrs, ctr_idx;
> +       u32 etype = pmu_get_perf_event_type(eidx);
> +       u64 config;
> +       struct kvm_pmc *pmc;
> +
> +       num_ctrs = kvpmu->num_fw_ctrs + kvpmu->num_hw_ctrs;
> +       if ((etype == PERF_TYPE_MAX) || ((ctr_base + __fls(ctr_mask)) >= num_ctrs))
> +               return -EINVAL;
> +
> +       if (pmu_is_fw_event(eidx))
> +               return -EOPNOTSUPP;
> +       /*
> +        * SKIP_MATCH flag indicates the caller is aware of the assigned counter
> +        * for this event. Just do a sanity check if it already marked used.
> +        */
> +       if (flag & SBI_PMU_CFG_FLAG_SKIP_MATCH) {
> +               if (!test_bit(ctr_base, kvpmu->used_pmc))
> +                       return -EINVAL;
> +               ctr_idx = ctr_base;
> +               goto match_done;
> +       }
> +
> +       ctr_idx = pmu_get_pmc_index(kvpmu, eidx, ctr_base, ctr_mask);
> +       if (ctr_idx < 0)
> +               return -EOPNOTSUPP;
> +
> +match_done:
> +       pmc = &kvpmu->pmc[ctr_idx];
> +       pmu_release_perf_event(pmc);
> +       pmc->idx = ctr_idx;
> +
> +       config = pmu_get_perf_event_config(eidx, edata);
> +       memset(&attr, 0, sizeof(struct perf_event_attr));
> +       attr.type = etype;
> +       attr.size = sizeof(attr);
> +       attr.pinned = true;
> +
> +       /*
> +        * It should never reach here if the platform doesn't support sscofpmf extensio
> +        * as mode filtering won't work without it.
> +        */
> +       attr.exclude_host = true;
> +       attr.exclude_hv = true;
> +       attr.exclude_user = flag & SBI_PMU_CFG_FLAG_SET_UINH ? 1 : 0;
> +       attr.exclude_kernel = flag & SBI_PMU_CFG_FLAG_SET_SINH ? 1 : 0;
> +       attr.config = config;
> +       attr.config1 = RISCV_KVM_PMU_CONFIG1_GUEST_EVENTS;
> +       if (flag & SBI_PMU_CFG_FLAG_CLEAR_VALUE) {
> +               //TODO: Do we really want to clear the value in hardware counter
> +               pmc->counter_val = 0;
> +       }
> +       /*
> +        * Set the default sample_period for now. The guest specified value
> +        * will be updated in the start call.
> +        */
> +       attr.sample_period = pmu_get_sample_period(pmc);
> +
> +       event = perf_event_create_kernel_counter(&attr, -1, current, NULL, pmc);
> +       if (IS_ERR(event)) {
> +               pr_err("kvm pmu event creation failed event %pe for eidx %lx\n", event, eidx);
> +               return -EOPNOTSUPP;
> +       }
> +
> +       set_bit(ctr_idx, kvpmu->used_pmc);
> +       pmc->perf_event = event;
> +       if (flag & SBI_PMU_CFG_FLAG_AUTO_START)
> +               perf_event_enable(pmc->perf_event);
> +
> +       return ctr_idx;
>  }
>
>  int kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu)
>  {
>         int i = 0, num_hw_ctrs, num_fw_ctrs, hpm_width;
>         struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> +       struct kvm_pmc *pmc;
>
>         if (!kvpmu)
>                 return -EINVAL;
> @@ -120,6 +392,7 @@ int kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu)
>                 return -EINVAL;
>         }
>
> +       bitmap_zero(kvpmu->used_pmc, RISCV_MAX_COUNTERS);
>         kvpmu->num_hw_ctrs = num_hw_ctrs;
>         kvpmu->num_fw_ctrs = num_fw_ctrs;
>         /*
> @@ -132,38 +405,49 @@ int kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu)
>                 /* TIME CSR shouldn't be read from perf interface */
>                 if (i == 1)
>                         continue;
> -               kvpmu->pmc[i].idx = i;
> -               kvpmu->pmc[i].vcpu = vcpu;
> +               pmc = &kvpmu->pmc[i];
> +               pmc->idx = i;
> +               pmc->counter_val = 0;
> +               pmc->vcpu = vcpu;
>                 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;
> +                               pmc->cinfo.width = 63;
>                         else
> -                               kvpmu->pmc[i].cinfo.width = hpm_width;
> +                               pmc->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.
>                          */
> -                       kvpmu->pmc[i].cinfo.csr = CSR_CYCLE + i;
> +                       pmc->cinfo.csr = CSR_CYCLE + i;
>                 } else {
> -                       kvpmu->pmc[i].cinfo.type = SBI_PMU_CTR_TYPE_FW;
> -                       kvpmu->pmc[i].cinfo.width = BITS_PER_LONG - 1;
> +                       pmc->cinfo.type = SBI_PMU_CTR_TYPE_FW;
> +                       pmc->cinfo.width = BITS_PER_LONG - 1;
>                 }
>         }
>
>         return 0;
>  }
>
> -void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu)
> +void kvm_riscv_vcpu_pmu_deinit(struct kvm_vcpu *vcpu)
>  {
> -       /* TODO */
> +       struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> +       struct kvm_pmc *pmc;
> +       int i;
> +
> +       if (!kvpmu)
> +               return;
> +
> +       for_each_set_bit(i, kvpmu->used_pmc, RISCV_MAX_COUNTERS) {
> +               pmc = &kvpmu->pmc[i];
> +               pmu_release_perf_event(pmc);
> +       }
>  }
>
> -void kvm_riscv_vcpu_pmu_deinit(struct kvm_vcpu *vcpu)
> +void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu)
>  {
> -       /* TODO */
> +       kvm_riscv_vcpu_pmu_deinit(vcpu);
>  }
> -
> --
> 2.25.1
>
>
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