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Message-ID: <CAHBxVyHk7zmhj_WfYaEyH_jFL02jZdobtwCTNAJFLNmg-OzvCg@mail.gmail.com>
Date: Wed, 10 Jan 2024 07:23:00 -0800
From: Atish Kumar Patra <atishp@...osinc.com>
To: Vladimir Isaev <vladimir.isaev@...tacore.com>
Cc: linux-kernel@...r.kernel.org, Albert Ou <aou@...s.berkeley.edu>,
Alexandre Ghiti <alexghiti@...osinc.com>, Andrew Jones <ajones@...tanamicro.com>,
Anup Patel <anup@...infault.org>, Atish Patra <atishp@...shpatra.org>,
Conor Dooley <conor.dooley@...rochip.com>, Guo Ren <guoren@...nel.org>,
Heiko Stuebner <heiko@...ech.de>, kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org,
linux-riscv@...ts.infradead.org, Mark Rutland <mark.rutland@....com>,
Palmer Dabbelt <palmer@...belt.com>, Paul Walmsley <paul.walmsley@...ive.com>,
Will Deacon <will@...nel.org>
Subject: Re: [v2 09/10] RISC-V: KVM: Add perf sampling support for guests
On Wed, Jan 10, 2024 at 4:38 AM Vladimir Isaev
<vladimir.isaev@...tacore.com> wrote:
>
>
> 30.12.2023 00:49, Atish Patra wrote:
> >
> > KVM enables perf for guest via counter virtualization. However, the
> > sampling can not be supported as there is no mechanism to enabled
> > trap/emulate scountovf in ISA yet. Rely on the SBI PMU snapshot
> > to provide the counter overflow data via the shared memory.
> >
> > In case of sampling event, the host first guest the LCOFI interrupt
> > and injects to the guest via irq filtering mechanism defined in AIA
> > specification. Thus, ssaia must be enabled in the host in order to
> > use perf sampling in the guest. No other AIA dpeendancy w.r.t kernel
> > is required.
> >
> > Signed-off-by: Atish Patra <atishp@...osinc.com>
> > ---
> > arch/riscv/include/asm/csr.h | 3 +-
> > arch/riscv/include/asm/kvm_vcpu_pmu.h | 1 +
> > arch/riscv/include/uapi/asm/kvm.h | 1 +
> > arch/riscv/kvm/main.c | 1 +
> > arch/riscv/kvm/vcpu.c | 8 +--
> > arch/riscv/kvm/vcpu_onereg.c | 2 +
> > arch/riscv/kvm/vcpu_pmu.c | 70 +++++++++++++++++++++++++--
> > 7 files changed, 77 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
> > index 88cdc8a3e654..bec09b33e2f0 100644
> > --- a/arch/riscv/include/asm/csr.h
> > +++ b/arch/riscv/include/asm/csr.h
> > @@ -168,7 +168,8 @@
> > #define VSIP_TO_HVIP_SHIFT (IRQ_VS_SOFT - IRQ_S_SOFT)
> > #define VSIP_VALID_MASK ((_AC(1, UL) << IRQ_S_SOFT) | \
> > (_AC(1, UL) << IRQ_S_TIMER) | \
> > - (_AC(1, UL) << IRQ_S_EXT))
> > + (_AC(1, UL) << IRQ_S_EXT) | \
> > + (_AC(1, UL) << IRQ_PMU_OVF))
> >
> > /* AIA CSR bits */
> > #define TOPI_IID_SHIFT 16
> > diff --git a/arch/riscv/include/asm/kvm_vcpu_pmu.h b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> > index d56b901a61fc..af6d0ff5ce41 100644
> > --- a/arch/riscv/include/asm/kvm_vcpu_pmu.h
> > +++ b/arch/riscv/include/asm/kvm_vcpu_pmu.h
> > @@ -36,6 +36,7 @@ struct kvm_pmc {
> > bool started;
> > /* Monitoring event ID */
> > unsigned long event_idx;
> > + struct kvm_vcpu *vcpu;
> > };
> >
> > /* PMU data structure per vcpu */
> > diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> > index d6b7a5b95874..d5aea43bc797 100644
> > --- a/arch/riscv/include/uapi/asm/kvm.h
> > +++ b/arch/riscv/include/uapi/asm/kvm.h
> > @@ -139,6 +139,7 @@ enum KVM_RISCV_ISA_EXT_ID {
> > KVM_RISCV_ISA_EXT_ZIHPM,
> > KVM_RISCV_ISA_EXT_SMSTATEEN,
> > KVM_RISCV_ISA_EXT_ZICOND,
> > + KVM_RISCV_ISA_EXT_SSCOFPMF,
> > KVM_RISCV_ISA_EXT_MAX,
> > };
> >
> > diff --git a/arch/riscv/kvm/main.c b/arch/riscv/kvm/main.c
> > index 225a435d9c9a..5a3a4cee0e3d 100644
> > --- a/arch/riscv/kvm/main.c
> > +++ b/arch/riscv/kvm/main.c
> > @@ -43,6 +43,7 @@ int kvm_arch_hardware_enable(void)
> > csr_write(CSR_HCOUNTEREN, 0x02);
> >
> > csr_write(CSR_HVIP, 0);
> > + csr_write(CSR_HVIEN, 1UL << IRQ_PMU_OVF);\
>
> Hi Atish,
>
> Maybe I missed something, but I thought you planned to move CSR_HVIEN to kvm_riscv_aia_enable() and
> add dependency for KVM sscofpmf and AIA since this register is part of AIA spec.
>
I already did that in the previous patch.
https://lore.kernel.org/all/20231229214950.4061381-9-atishp@rivosinc.com/
I am not sure how this line got into this patch. My bad! Thanks for noticing it.
I will send a fixed version right away.
> Thank you
> Vladimir Isaev
>
> >
> > kvm_riscv_aia_enable();
> >
> > diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> > index b5ca9f2e98ac..f83f0226439f 100644
> > --- a/arch/riscv/kvm/vcpu.c
> > +++ b/arch/riscv/kvm/vcpu.c
> > @@ -382,7 +382,8 @@ int kvm_riscv_vcpu_set_interrupt(struct kvm_vcpu *vcpu, unsigned int irq)
> > if (irq < IRQ_LOCAL_MAX &&
> > irq != IRQ_VS_SOFT &&
> > irq != IRQ_VS_TIMER &&
> > - irq != IRQ_VS_EXT)
> > + irq != IRQ_VS_EXT &&
> > + irq != IRQ_PMU_OVF)
> > return -EINVAL;
> >
> > set_bit(irq, vcpu->arch.irqs_pending);
> > @@ -397,14 +398,15 @@ int kvm_riscv_vcpu_set_interrupt(struct kvm_vcpu *vcpu, unsigned int irq)
> > int kvm_riscv_vcpu_unset_interrupt(struct kvm_vcpu *vcpu, unsigned int irq)
> > {
> > /*
> > - * We only allow VS-mode software, timer, and external
> > + * We only allow VS-mode software, timer, counter overflow and external
> > * interrupts when irq is one of the local interrupts
> > * defined by RISC-V privilege specification.
> > */
> > if (irq < IRQ_LOCAL_MAX &&
> > irq != IRQ_VS_SOFT &&
> > irq != IRQ_VS_TIMER &&
> > - irq != IRQ_VS_EXT)
> > + irq != IRQ_VS_EXT &&
> > + irq != IRQ_PMU_OVF)
> > return -EINVAL;
> >
> > clear_bit(irq, vcpu->arch.irqs_pending);
> > diff --git a/arch/riscv/kvm/vcpu_onereg.c b/arch/riscv/kvm/vcpu_onereg.c
> > index 581568847910..1eaaa919aa61 100644
> > --- a/arch/riscv/kvm/vcpu_onereg.c
> > +++ b/arch/riscv/kvm/vcpu_onereg.c
> > @@ -36,6 +36,7 @@ static const unsigned long kvm_isa_ext_arr[] = {
> > /* Multi letter extensions (alphabetically sorted) */
> > KVM_ISA_EXT_ARR(SMSTATEEN),
> > KVM_ISA_EXT_ARR(SSAIA),
> > + KVM_ISA_EXT_ARR(SSCOFPMF),
> > KVM_ISA_EXT_ARR(SSTC),
> > KVM_ISA_EXT_ARR(SVINVAL),
> > KVM_ISA_EXT_ARR(SVNAPOT),
> > @@ -88,6 +89,7 @@ static bool kvm_riscv_vcpu_isa_disable_allowed(unsigned long ext)
> > case KVM_RISCV_ISA_EXT_I:
> > case KVM_RISCV_ISA_EXT_M:
> > case KVM_RISCV_ISA_EXT_SSTC:
> > + case KVM_RISCV_ISA_EXT_SSCOFPMF:
> > case KVM_RISCV_ISA_EXT_SVINVAL:
> > case KVM_RISCV_ISA_EXT_SVNAPOT:
> > case KVM_RISCV_ISA_EXT_ZBA:
> > diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> > index e980235b8436..f2bf5b5bdd61 100644
> > --- a/arch/riscv/kvm/vcpu_pmu.c
> > +++ b/arch/riscv/kvm/vcpu_pmu.c
> > @@ -229,6 +229,47 @@ static int kvm_pmu_validate_counter_mask(struct kvm_pmu *kvpmu, unsigned long ct
> > return 0;
> > }
> >
> > +static void kvm_riscv_pmu_overflow(struct perf_event *perf_event,
> > + struct perf_sample_data *data,
> > + struct pt_regs *regs)
> > +{
> > + struct kvm_pmc *pmc = perf_event->overflow_handler_context;
> > + struct kvm_vcpu *vcpu = pmc->vcpu;
> > + struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
> > + struct riscv_pmu *rpmu = to_riscv_pmu(perf_event->pmu);
> > + u64 period;
> > +
> > + /*
> > + * Stop the event counting by directly accessing the perf_event.
> > + * Otherwise, this needs to deferred via a workqueue.
> > + * That will introduce skew in the counter value because the actual
> > + * physical counter would start after returning from this function.
> > + * It will be stopped again once the workqueue is scheduled
> > + */
> > + rpmu->pmu.stop(perf_event, PERF_EF_UPDATE);
> > +
> > + /*
> > + * The hw counter would start automatically when this function returns.
> > + * Thus, the host may continue to interrupt and inject it to the guest
> > + * even without the guest configuring the next event. Depending on the hardware
> > + * the host may have some sluggishness only if privilege mode filtering is not
> > + * available. In an ideal world, where qemu is not the only capable hardware,
> > + * this can be removed.
> > + * FYI: ARM64 does this way while x86 doesn't do anything as such.
> > + * TODO: Should we keep it for RISC-V ?
> > + */
> > + period = -(local64_read(&perf_event->count));
> > +
> > + local64_set(&perf_event->hw.period_left, 0);
> > + perf_event->attr.sample_period = period;
> > + perf_event->hw.sample_period = period;
> > +
> > + set_bit(pmc->idx, kvpmu->pmc_overflown);
> > + kvm_riscv_vcpu_set_interrupt(vcpu, IRQ_PMU_OVF);
> > +
> > + rpmu->pmu.start(perf_event, PERF_EF_RELOAD);
> > +}
> > +
> > static long kvm_pmu_create_perf_event(struct kvm_pmc *pmc, struct perf_event_attr *attr,
> > unsigned long flags, unsigned long eidx,
> > unsigned long evtdata)
> > @@ -248,7 +289,7 @@ static long kvm_pmu_create_perf_event(struct kvm_pmc *pmc, struct perf_event_att
> > */
> > attr->sample_period = kvm_pmu_get_sample_period(pmc);
> >
> > - event = perf_event_create_kernel_counter(attr, -1, current, NULL, pmc);
> > + event = perf_event_create_kernel_counter(attr, -1, current, kvm_riscv_pmu_overflow, pmc);
> > if (IS_ERR(event)) {
> > pr_err("kvm pmu event creation failed for eidx %lx: %ld\n", eidx, PTR_ERR(event));
> > return PTR_ERR(event);
> > @@ -473,6 +514,12 @@ int kvm_riscv_vcpu_pmu_ctr_start(struct kvm_vcpu *vcpu, unsigned long ctr_base,
> > }
> > }
> >
> > + /* The guest have serviced the interrupt and starting the counter again */
> > + if (test_bit(IRQ_PMU_OVF, vcpu->arch.irqs_pending)) {
> > + clear_bit(pmc_index, kvpmu->pmc_overflown);
> > + kvm_riscv_vcpu_unset_interrupt(vcpu, IRQ_PMU_OVF);
> > + }
> > +
> > out:
> > retdata->err_val = sbiret;
> >
> > @@ -539,7 +586,13 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
> > else if (pmc->perf_event)
> > pmc->counter_val += perf_event_read_value(pmc->perf_event,
> > &enabled, &running);
> > - /* TODO: Add counter overflow support when sscofpmf support is added */
> > + /*
> > + * The counter and overflow indicies in the snapshot region are w.r.to
> > + * cbase. Modify the set bit in the counter mask instead of the pmc_index
> > + * which indicates the absolute counter index.
> > + */
> > + if (test_bit(pmc_index, kvpmu->pmc_overflown))
> > + kvpmu->sdata->ctr_overflow_mask |= (1UL << i);
> > kvpmu->sdata->ctr_values[i] = pmc->counter_val;
> > kvm_vcpu_write_guest(vcpu, kvpmu->snapshot_addr, kvpmu->sdata,
> > sizeof(struct riscv_pmu_snapshot_data));
> > @@ -548,15 +601,20 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
> > if (flags & SBI_PMU_STOP_FLAG_RESET) {
> > pmc->event_idx = SBI_PMU_EVENT_IDX_INVALID;
> > clear_bit(pmc_index, kvpmu->pmc_in_use);
> > + clear_bit(pmc_index, kvpmu->pmc_overflown);
> > if (snap_flag_set) {
> > /* Clear the snapshot area for the upcoming deletion event */
> > kvpmu->sdata->ctr_values[i] = 0;
> > + /*
> > + * Only clear the given counter as the caller is responsible to
> > + * validate both the overflow mask and configured counters.
> > + */
> > + kvpmu->sdata->ctr_overflow_mask &= ~(1UL << i);
> > kvm_vcpu_write_guest(vcpu, kvpmu->snapshot_addr, kvpmu->sdata,
> > sizeof(struct riscv_pmu_snapshot_data));
> > }
> > }
> > }
> > -
> > out:
> > retdata->err_val = sbiret;
> >
> > @@ -699,6 +757,7 @@ void kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu)
> > pmc = &kvpmu->pmc[i];
> > pmc->idx = i;
> > pmc->event_idx = SBI_PMU_EVENT_IDX_INVALID;
> > + pmc->vcpu = vcpu;
> > if (i < kvpmu->num_hw_ctrs) {
> > pmc->cinfo.type = SBI_PMU_CTR_TYPE_HW;
> > if (i < 3)
> > @@ -731,13 +790,14 @@ void kvm_riscv_vcpu_pmu_deinit(struct kvm_vcpu *vcpu)
> > if (!kvpmu)
> > return;
> >
> > - for_each_set_bit(i, kvpmu->pmc_in_use, RISCV_MAX_COUNTERS) {
> > + for_each_set_bit(i, kvpmu->pmc_in_use, RISCV_KVM_MAX_COUNTERS) {
> > pmc = &kvpmu->pmc[i];
> > pmc->counter_val = 0;
> > kvm_pmu_release_perf_event(pmc);
> > pmc->event_idx = SBI_PMU_EVENT_IDX_INVALID;
> > }
> > - bitmap_zero(kvpmu->pmc_in_use, RISCV_MAX_COUNTERS);
> > + bitmap_zero(kvpmu->pmc_in_use, RISCV_KVM_MAX_COUNTERS);
> > + bitmap_zero(kvpmu->pmc_overflown, RISCV_KVM_MAX_COUNTERS);
> > memset(&kvpmu->fw_event, 0, SBI_PMU_FW_MAX * sizeof(struct kvm_fw_event));
> > kvm_pmu_clear_snapshot_area(vcpu);
> > }
> > --
> > 2.34.1
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
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