Hi Marc,
On 9/8/20 9:58 AM, Marc Zyngier wrote:
> The PMU code suffers from a small defect where we assume that the event
> number provided by the guest is always 16 bit wide, even if the CPU only
> implements the ARMv8.0 architecture. This isn't really problematic in
> the sense that the event number ends up in a system register, cropping
> it to the right width, but still this needs fixing.
>
> In order to make it work, let's probe the version of the PMU that the
> guest is going to use. This is done by temporarily creating a kernel
> event and looking at the PMUVer field that has been saved at probe time
> in the associated arm_pmu structure. This in turn gets saved in the kvm
> structure, and subsequently used to compute the event mask that gets
> used throughout the PMU code.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> arch/arm64/include/asm/kvm_host.h | 2 +
> arch/arm64/kvm/pmu-emul.c | 81 +++++++++++++++++++++++++++++--
> 2 files changed, 78 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 65568b23868a..6cd60be69c28 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -110,6 +110,8 @@ struct kvm_arch {
> * supported.
> */
> bool return_nisv_io_abort_to_user;
> +
> + unsigned int pmuver;
> };
>
> struct kvm_vcpu_fault_info {
> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> index 93d797df42c6..8a5f65763814 100644
> --- a/arch/arm64/kvm/pmu-emul.c
> +++ b/arch/arm64/kvm/pmu-emul.c
> @@ -20,6 +20,20 @@ static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc);
>
> #define PERF_ATTR_CFG1_KVM_PMU_CHAINED 0x1
>
> +static u32 kvm_pmu_event_mask(struct kvm *kvm)
> +{
> + switch (kvm->arch.pmuver) {
> + case 1: /* ARMv8.0 */
> + return GENMASK(9, 0);
> + case 4: /* ARMv8.1 */
> + case 5: /* ARMv8.4 */
> + case 6: /* ARMv8.5 */
> + return GENMASK(15, 0);
> + default: /* Shouldn't be there, just for sanity */
> + return 0;
> + }
> +}
> +
> /**
> * kvm_pmu_idx_is_64bit - determine if select_idx is a 64bit counter
> * @vcpu: The vcpu pointer
> @@ -100,7 +114,7 @@ static bool kvm_pmu_idx_has_chain_evtype(struct kvm_vcpu *vcpu, u64 select_idx)
> return false;
>
> reg = PMEVTYPER0_EL0 + select_idx;
> - eventsel = __vcpu_sys_reg(vcpu, reg) & ARMV8_PMU_EVTYPE_EVENT;
> + eventsel = __vcpu_sys_reg(vcpu, reg) & kvm_pmu_event_mask(vcpu->kvm);
>
> return eventsel == ARMV8_PMUV3_PERFCTR_CHAIN;
> }
> @@ -495,7 +509,7 @@ void kvm_pmu_software_increment(struct kvm_vcpu *vcpu, u64 val)
>
> /* PMSWINC only applies to ... SW_INC! */
> type = __vcpu_sys_reg(vcpu, PMEVTYPER0_EL0 + i);
> - type &= ARMV8_PMU_EVTYPE_EVENT;
> + type &= kvm_pmu_event_mask(vcpu->kvm);
> if (type != ARMV8_PMUV3_PERFCTR_SW_INCR)
> continue;
>
> @@ -578,7 +592,7 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx)
> data = __vcpu_sys_reg(vcpu, reg);
>
> kvm_pmu_stop_counter(vcpu, pmc);
> - eventsel = data & ARMV8_PMU_EVTYPE_EVENT;
> + eventsel = data & kvm_pmu_event_mask(vcpu->kvm);;
>
> /* Software increment event does't need to be backed by a perf event */
> if (eventsel == ARMV8_PMUV3_PERFCTR_SW_INCR &&
> @@ -679,17 +693,68 @@ static void kvm_pmu_update_pmc_chained(struct kvm_vcpu *vcpu, u64 select_idx)
> void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data,
> u64 select_idx)
> {
> - u64 reg, event_type = data & ARMV8_PMU_EVTYPE_MASK;
> + u64 reg, mask;
> +
> + mask = ARMV8_PMU_EVTYPE_MASK;
> + mask &= ~ARMV8_PMU_EVTYPE_EVENT;
> + mask |= kvm_pmu_event_mask(vcpu->kvm);
>
> reg = (select_idx == ARMV8_PMU_CYCLE_IDX)
> ? PMCCFILTR_EL0 : PMEVTYPER0_EL0 + select_idx;
>
> - __vcpu_sys_reg(vcpu, reg) = event_type;
> + __vcpu_sys_reg(vcpu, reg) = data & mask;
>
> kvm_pmu_update_pmc_chained(vcpu, select_idx);
> kvm_pmu_create_perf_event(vcpu, select_idx);
> }
>
> +static int kvm_pmu_probe_pmuver(void)
> +{
> + struct perf_event_attr attr = { };
> + struct perf_event *event;
> + struct arm_pmu *pmu;
> + int pmuver = 0xf;
> +
> + /*
> + * Create a dummy event that only counts user cycles. As we'll never
> + * leave thing function with the event being live, it will never
> + * count anything. But it allows us to probe some of the PMU
> + * details. Yes, this is terrible.
I fail to understand why we can't directly read ID_DFR0_EL1.PerfMon?
Thanks
Eric
> + */
> + attr.type = PERF_TYPE_RAW;
> + attr.size = sizeof(attr);
> + attr.pinned = 1;
> + attr.disabled = 0;
> + attr.exclude_user = 0;
> + attr.exclude_kernel = 1;
> + attr.exclude_hv = 1;
> + attr.exclude_host = 1;
> + attr.config = ARMV8_PMUV3_PERFCTR_CPU_CYCLES;
> + attr.sample_period = GENMASK(63, 0);
> +
> + event = perf_event_create_kernel_counter(&attr, -1, current,
> + kvm_pmu_perf_overflow, &attr);
> +
> + if (IS_ERR(event)) {
> + pr_err_once("kvm: pmu event creation failed %ld\n",
> + PTR_ERR(event));
> + return 0xf;
> + }
> +
> + if (event->pmu) {
> + pmu = to_arm_pmu(event->pmu);
> + if (pmu->pmuver)
> + pmuver = pmu->pmuver;
> + pr_debug("PMU on CPUs %*pbl version %x\n",
> + cpumask_pr_args(&pmu->supported_cpus), pmuver);
> + }
> +
> + perf_event_disable(event);
> + perf_event_release_kernel(event);
> +
> + return pmuver;
> +}
> +
> bool kvm_arm_support_pmu_v3(void)
> {
> /*
> @@ -796,6 +861,12 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
> if (vcpu->arch.pmu.created)
> return -EBUSY;
>
> + if (!vcpu->kvm->arch.pmuver)
> + vcpu->kvm->arch.pmuver = kvm_pmu_probe_pmuver();
> +
> + if (vcpu->kvm->arch.pmuver == 0xf)
> + return -ENODEV;
> +
> switch (attr->attr) {
> case KVM_ARM_VCPU_PMU_V3_IRQ: {
> int __user *uaddr = (int __user *)(long)attr->addr;
>
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