Re: [RFC 8/9] RISC-V: KVM: Implement perf support

Atish Patra
2022-09-23T21:05:18Z

On Mon, Sep 19, 2022 at 7:24 PM Eric Lin <eric.lin@sifive.com> wrote:
>
> 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;
>

Yes. Thanks for the catch.
The sample_period should be (-pmc->counter_val) & counter_val_mask.

I will revise the patch along with a few other fixes and send the v2.

> 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
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv

--
Regards,
Atish