[RFC 8/9] RISC-V: KVM: Add perf sampling support for guests
Atish Kumar Patra
atishp at rivosinc.com
Sat Dec 16 17:48:59 PST 2023
On Thu, Dec 14, 2023 at 8:02 AM Anup Patel <anup at brainfault.org> wrote:
>
> On Tue, Dec 5, 2023 at 8:13 AM Atish Patra <atishp at rivosinc.com> 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
>
> s/dpeendancy/dependency/
>
Fixed.
> > is required.
> >
> > Signed-off-by: Atish Patra <atishp at rivosinc.com>
> > ---
> > arch/riscv/include/asm/csr.h | 3 +-
> > 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 | 1 +
> > arch/riscv/kvm/vcpu_pmu.c | 69 ++++++++++++++++++++++++++++---
> > 6 files changed, 73 insertions(+), 10 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/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> > index 60d3b21dead7..741c16f4518e 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);
> >
> > kvm_riscv_aia_enable();
> >
> > diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> > index e087c809073c..2d9f252356c3 100644
> > --- a/arch/riscv/kvm/vcpu.c
> > +++ b/arch/riscv/kvm/vcpu.c
> > @@ -380,7 +380,8 @@ 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);
> > @@ -395,14 +396,15 @@ 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 f8c9fa0c03c5..19a0e4eaf0df 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),
>
> Sscofpmf can't be disabled for guest so we should add it to
> kvm_riscv_vcpu_isa_disable_allowed(), no ?
>
Just to clarify it can't be disabled from the kvm user space via one
reg interface if kvm already exposes
it to the guest. However, Kvm will not expose Sscofpmf to the guest if
Ssaia is not available.
I have added these fixes in the next version.
> > KVM_ISA_EXT_ARR(SSTC),
> > KVM_ISA_EXT_ARR(SVINVAL),
> > KVM_ISA_EXT_ARR(SVNAPOT),
> > diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> > index 622c4ee89e7b..86c8e92f92d3 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;
>
> Ahh, the "vcpu" field is used here. Move that change from
> patch7 to this patch.
>
done.
> > + 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 interrupts and inject it to the guest
> > + * even without guest configuring the next event. Depending on the hardware
> > + * the host may 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 int kvm_pmu_create_perf_event(struct kvm_pmc *pmc, struct perf_event_attr *attr,
> > unsigned long flags, unsigned long eidx, unsigned long evtdata)
> > {
> > @@ -247,7 +288,7 @@ static int kvm_pmu_create_perf_event(struct kvm_pmc *pmc, struct perf_event_attr
> > */
> > 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);
> > @@ -466,6 +507,12 @@ 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;
> >
> > @@ -537,7 +584,12 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
> > }
> >
> > if (bSnapshot && !sbiret) {
> > - //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.
> > + */
>
> Use a double winged comment block here.
>
> > + 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));
> > @@ -546,15 +598,19 @@ 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 (bSnapshot) {
> > /* 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.
> > + */
>
> Use a double winged comment block here.
>
Fixed all the comment styling.
> > + 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;
> >
> > @@ -729,15 +785,16 @@ 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));
> > - kvpmu->snapshot_addr = INVALID_GPA;
> > + kvm_pmu_clear_snapshot_area(vcpu);
> > }
> >
> > void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu)
> > --
> > 2.34.1
> >
>
> Regards,
> Anup
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