Re: [PATCH v2 1/2] KVM: arm64: Add PMU event filtering infrastructure
From: Auger Eric <eric.auger@redhat.com>
Date: 2020-03-10 17:40:51
Also in:
kvm, kvmarm
Hi Marc, On 3/10/20 12:03 PM, Marc Zyngier wrote:
Hi Eric, On 2020-03-09 18:05, Auger Eric wrote:quoted
Hi Marc, On 3/9/20 1:48 PM, Marc Zyngier wrote:quoted
It can be desirable to expose a PMU to a guest, and yet not want the guest to be able to count some of the implemented events (because this would give information on shared resources, for example. For this, let's extend the PMUv3 device API, and offer a way to setup a bitmap of the allowed events (the default being no bitmap, and thus no filtering). Userspace can thus allow/deny ranges of event. The default policy depends on the "polarity" of the first filter setup (default deny if the filter allows events, and default allow if the filter denies events). This allows to setup exactly what is allowed for a given guest. Note that although the ioctl is per-vcpu, the map of allowed events is global to the VM (it can be setup from any vcpu until the vcpu PMU is initialized). Signed-off-by: Marc Zyngier <maz@kernel.org> --- arch/arm64/include/asm/kvm_host.h | 6 +++ arch/arm64/include/uapi/asm/kvm.h | 16 ++++++ virt/kvm/arm/arm.c | 2 + virt/kvm/arm/pmu.c | 84 +++++++++++++++++++++++++------ 4 files changed, 92 insertions(+), 16 deletions(-)diff --git a/arch/arm64/include/asm/kvm_host.hb/arch/arm64/include/asm/kvm_host.h index 57fd46acd058..8e63c618688d 100644--- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h@@ -91,6 +91,12 @@ struct kvm_arch {* supported. */ bool return_nisv_io_abort_to_user; + + /* + * VM-wide PMU filter, implemented as a bitmap and big enough + * for up to 65536 events + */ + unsigned long *pmu_filter; }; #define KVM_NR_MEM_OBJS 40diff --git a/arch/arm64/include/uapi/asm/kvm.hb/arch/arm64/include/uapi/asm/kvm.h index ba85bb23f060..7b1511d6ce44 100644--- a/arch/arm64/include/uapi/asm/kvm.h +++ b/arch/arm64/include/uapi/asm/kvm.h@@ -159,6 +159,21 @@ struct kvm_sync_regs {struct kvm_arch_memory_slot { }; +/* + * PMU filter structure. Describe a range of events with a particular + * action. To be used with KVM_ARM_VCPU_PMU_V3_FILTER. + */ +struct kvm_pmu_event_filter { + __u16 base_event; + __u16 nevents; + +#define KVM_PMU_EVENT_ALLOW 0 +#define KVM_PMU_EVENT_DENY 1 + + __u8 action; + __u8 pad[3]; +}; + /* for KVM_GET/SET_VCPU_EVENTS */ struct kvm_vcpu_events { struct {@@ -329,6 +344,7 @@ struct kvm_vcpu_events {#define KVM_ARM_VCPU_PMU_V3_CTRL 0 #define KVM_ARM_VCPU_PMU_V3_IRQ 0 #define KVM_ARM_VCPU_PMU_V3_INIT 1 +#define KVM_ARM_VCPU_PMU_V3_FILTER 2 #define KVM_ARM_VCPU_TIMER_CTRL 1 #define KVM_ARM_VCPU_TIMER_IRQ_VTIMER 0 #define KVM_ARM_VCPU_TIMER_IRQ_PTIMER 1diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c index eda7b624eab8..8d849ac88a44 100644 --- a/virt/kvm/arm/arm.c +++ b/virt/kvm/arm/arm.c@@ -164,6 +164,8 @@ void kvm_arch_destroy_vm(struct kvm *kvm)free_percpu(kvm->arch.last_vcpu_ran); kvm->arch.last_vcpu_ran = NULL; + bitmap_free(kvm->arch.pmu_filter); + for (i = 0; i < KVM_MAX_VCPUS; ++i) { if (kvm->vcpus[i]) { kvm_vcpu_destroy(kvm->vcpus[i]);diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c index f0d0312c0a55..9f0fd0224d5b 100644 --- a/virt/kvm/arm/pmu.c +++ b/virt/kvm/arm/pmu.c@@ -579,10 +579,19 @@ static void kvm_pmu_create_perf_event(structkvm_vcpu *vcpu, u64 select_idx) kvm_pmu_stop_counter(vcpu, pmc); eventsel = data & ARMV8_PMU_EVTYPE_EVENT; + if (pmc->idx == ARMV8_PMU_CYCLE_IDX) + eventsel = ARMV8_PMUV3_PERFCTR_CPU_CYCLES;nit: if (pmc->idx == ARMV8_PMU_CYCLE_IDX) eventsel = ARMV8_PMUV3_PERFCTR_CPU_CYCLES; else eventsel = data & ARMV8_PMU_EVTYPE_EVENT;You don't like it? ;-)
? eventset set only once instead of 2 times
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/* Software increment event does't need to be backed by a perf event */nit: while wer are at it fix the does't typoquoted
- if (eventsel == ARMV8_PMUV3_PERFCTR_SW_INCR && - pmc->idx != ARMV8_PMU_CYCLE_IDX) + if (eventsel == ARMV8_PMUV3_PERFCTR_SW_INCR) + return; + + /* + * If we have a filter in place and that the event isn't allowed, do + * not install a perf event either. + */ + if (vcpu->kvm->arch.pmu_filter && + !test_bit(eventsel, vcpu->kvm->arch.pmu_filter)) return; memset(&attr, 0, sizeof(struct perf_event_attr));@@ -594,8 +603,7 @@ static void kvm_pmu_create_perf_event(structkvm_vcpu *vcpu, u64 select_idx) attr.exclude_kernel = data & ARMV8_PMU_EXCLUDE_EL1 ? 1 : 0; attr.exclude_hv = 1; /* Don't count EL2 events */ attr.exclude_host = 1; /* Don't count host events */ - attr.config = (pmc->idx == ARMV8_PMU_CYCLE_IDX) ? - ARMV8_PMUV3_PERFCTR_CPU_CYCLES : eventsel; + attr.config = eventsel;So in that case the guest counter will not increment but the guest does not know the counter is not implemented. Can't this lead to bad user experience. Shouldn't this disablement be reflected in PMCEID0/1 regs?The whole point is that we want to keep things hidden from the guest. Also, PMCEID{0,1} only describe a small set of events (the architected common events), and not the whole range of microarchitectural events that the CPU implements.
I am still not totally convinced. Things are not totally hidden to the guest as the counter does not increment, right? So a guest may try to use as it is advertised in PMCEID0/1 but not get the expected results leading to potential support request. I agree not all the events are described there but your API also allows to filter out some of the ones that are advertised.
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counter = kvm_pmu_get_pair_counter_value(vcpu, pmc);@@ -735,15 +743,6 @@ int kvm_arm_pmu_v3_enable(struct kvm_vcpu *vcpu)static int kvm_arm_pmu_v3_init(struct kvm_vcpu *vcpu) { - if (!kvm_arm_support_pmu_v3()) - return -ENODEV; - - if (!test_bit(KVM_ARM_VCPU_PMU_V3, vcpu->arch.features)) - return -ENXIO; - - if (vcpu->arch.pmu.created) - return -EBUSY; - if (irqchip_in_kernel(vcpu->kvm)) { int ret;@@ -794,8 +793,19 @@ static bool pmu_irq_is_valid(struct kvm *kvm,int irq) return true; } +#define NR_EVENTS (ARMV8_PMU_EVTYPE_EVENT + 1) + int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr) { + if (!kvm_arm_support_pmu_v3()) + return -ENODEV; + + if (!test_bit(KVM_ARM_VCPU_PMU_V3, vcpu->arch.features)) + return -ENODEV;I see you changed -ENXIO into -ENODEV. wanted?Probably not... but see below.quoted
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+ + if (vcpu->arch.pmu.created) + return -EBUSY; + switch (attr->attr) { case KVM_ARM_VCPU_PMU_V3_IRQ: { int __user *uaddr = (int __user *)(long)attr->addr;@@ -804,9 +814,6 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu*vcpu, struct kvm_device_attr *attr) if (!irqchip_in_kernel(vcpu->kvm)) return -EINVAL; - if (!test_bit(KVM_ARM_VCPU_PMU_V3, vcpu->arch.features)) - return -ENODEV; -Here's why. I wonder if we already have a problem with the consistency of the error codes returned to userspace.
OK. Then you may document it in the commit message?
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if (get_user(irq, uaddr)) return -EFAULT;@@ -824,6 +831,50 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu*vcpu, struct kvm_device_attr *attr) vcpu->arch.pmu.irq_num = irq; return 0; } + case KVM_ARM_VCPU_PMU_V3_FILTER: { + struct kvm_pmu_event_filter __user *uaddr; + struct kvm_pmu_event_filter filter; + + uaddr = (struct kvm_pmu_event_filter __user *)(long)attr->addr; + + if (copy_from_user(&filter, uaddr, sizeof(filter))) + return -EFAULT; + + if (((u32)filter.base_event + filter.nevents) > NR_EVENTS ||isnt't it >= ?No, I think this is correct. I want to be able to filter event 0xFFFF, for example, so I have base_event=0xFFFF and nevents=1.
hum my mistake. Sorry
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+ (filter.action != KVM_PMU_EVENT_ALLOW && + filter.action != KVM_PMU_EVENT_DENY)) + return -EINVAL;-EINVAL is not documented in the API doc.Good point.quoted
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+ + mutex_lock(&vcpu->kvm->lock); + + if (!vcpu->kvm->arch.pmu_filter) { + vcpu->kvm->arch.pmu_filter = bitmap_alloc(NR_EVENTS, GFP_KERNEL); + if (!vcpu->kvm->arch.pmu_filter) { + mutex_unlock(&vcpu->kvm->lock); + return -ENOMEM; + } + + /* + * The default depends on the first applied filter. + * If it allows events, the default is to deny. + * Conversely, if the first filter denies a set of + * events, the default is to allow. + */ + if (filter.action == KVM_PMU_EVENT_ALLOW) + bitmap_zero(vcpu->kvm->arch.pmu_filter, NR_EVENTS); + else + bitmap_fill(vcpu->kvm->arch.pmu_filter, NR_EVENTS); + } + + if (filter.action == KVM_PMU_EVENT_ALLOW) + bitmap_set(vcpu->kvm->arch.pmu_filter, filter.base_event, filter.nevents); + else + bitmap_clear(vcpu->kvm->arch.pmu_filter, filter.base_event, filter.nevents); + + mutex_unlock(&vcpu->kvm->lock); + + return 0; + } case KVM_ARM_VCPU_PMU_V3_INIT: return kvm_arm_pmu_v3_init(vcpu); }@@ -860,6 +911,7 @@ int kvm_arm_pmu_v3_has_attr(struct kvm_vcpu*vcpu, struct kvm_device_attr *attr) switch (attr->attr) { case KVM_ARM_VCPU_PMU_V3_IRQ:not related to this patch but shouldn't we advertise this only with in-kernel irqchip?We do support the PMU without the in-kernel chip, unfortunately... Yes, supporting this feature was a big mistake.
But I see in kvm_arm_pmu_v3_set_attr:
case KVM_ARM_VCPU_PMU_V3_IRQ:
../..
if (!irqchip_in_kernel(vcpu->kvm))
return -EINVAL;
Thanks
Eric
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case KVM_ARM_VCPU_PMU_V3_INIT: + case KVM_ARM_VCPU_PMU_V3_FILTER: if (kvm_arm_support_pmu_v3() && test_bit(KVM_ARM_VCPU_PMU_V3, vcpu->arch.features)) return 0;Thanks for the review, M.
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