Subject: [PATCH 07/18] KVM: ARM64: PMU: Add perf event map and introduce perf event creating function

From: [email-masked] (Christoffer Dall)
Date: Mon, 3 Aug 2015 21:55:47 +0200

On Tue, Jul 21, 2015 at 09:35:03AM +0800, Shannon Zhao wrote:
> 
> 
> On 2015/7/17 22:30, Christoffer Dall wrote:
> > On Mon, Jul 06, 2015 at 10:17:37AM +0800, shannon.zhao at linaro.org wrote:
> >> From: Shannon Zhao <[email-masked]>
> >>
> >> When we use tools like perf on host, perf passes the event type and the
> >> id in this type category to kernel, then kernel will map them to event
> >> number and write this number to PMU PMEVTYPER<n>_EL0 register. While
> >> we're trapping and emulating guest accesses to PMU registers, we get the
> >> event number and map it to the event type and the id reversely.
> > 
> > There's something with the nomenclature that makes this really hard to
> > read.
> > 
> > you mention here: "event type", "the id", and "event number".  The
> > former two I think are perf identifiers, and the latter is the hardware
> > event number, is this right?
> > 
> 
> Yeah, right.
> 

ok, if we can clarify our nomenclature throughout here I think that
would make the patches easier to understand/read.

> >>
> >> Check whether the event type is same with the one to be set.
> > 
> > when?
> > 
> In function kvm_pmu_set_counter_event_type before create a new perf event.

do you mean when the guest configures some counter and we we create a
perf event accordingly?

If so, I think this could be clarified in the commit text.

> 
> >> +	if ((data & ARMV8_EVTYPE_EVENT) == pmc->eventsel)
> >> +		return;
> 
> 
> >> If not,
> >> stop counter to monitor current event and find the event type map id.
> >> According to the bits of data to configure this perf_event attr and
> >> set exclude_host to 1 for guest. Then call perf_event API to create the
> >> corresponding event and save the event pointer.
> >>
> >> Signed-off-by: Shannon Zhao <[email-masked]>
> >> ---
> >>  include/kvm/arm_pmu.h |   4 ++
> >>  virt/kvm/arm/pmu.c    | 173 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >>  2 files changed, 177 insertions(+)
> >>
> >> diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> >> index 27d14ca..1050b24 100644
> >> --- a/include/kvm/arm_pmu.h
> >> +++ b/include/kvm/arm_pmu.h
> >> @@ -45,9 +45,13 @@ struct kvm_pmu {
> >>  
> >>  #ifdef CONFIG_KVM_ARM_PMU
> >>  void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu);
> >> +void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, unsigned long data,
> >> +				    unsigned long select_idx);
> >>  void kvm_pmu_init(struct kvm_vcpu *vcpu);
> >>  #else
> >>  static inline void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu) {}
> >> +void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, unsigned long data,
> >> +				    unsigned long select_idx) {}
> >>  static inline void kvm_pmu_init(struct kvm_vcpu *vcpu) {}
> >>  #endif
> >>  
> >> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> >> index dc252d0..50a3c82 100644
> >> --- a/virt/kvm/arm/pmu.c
> >> +++ b/virt/kvm/arm/pmu.c
> >> @@ -18,8 +18,68 @@
> >>  #include <linux/cpu.h>
> >>  #include <linux/kvm.h>
> >>  #include <linux/kvm_host.h>
> >> +#include <linux/perf_event.h>
> >>  #include <kvm/arm_pmu.h>
> >>  
> >> +/* PMU HW events mapping. */
> >> +static struct kvm_pmu_hw_event_map {
> >> +	unsigned eventsel;
> >> +	unsigned event_type;
> >> +} kvm_pmu_hw_events[] = {
> >> +	[0] = { 0x11, PERF_COUNT_HW_CPU_CYCLES },
> >> +	[1] = { 0x08, PERF_COUNT_HW_INSTRUCTIONS },
> >> +	[2] = { 0x04, PERF_COUNT_HW_CACHE_REFERENCES },
> >> +	[3] = { 0x03, PERF_COUNT_HW_CACHE_MISSES },
> >> +	[4] = { 0x10, PERF_COUNT_HW_BRANCH_MISSES },
> >> +};
> >> +
> >> +/* PMU HW cache events mapping. */
> >> +static struct kvm_pmu_hw_cache_event_map {
> >> +	unsigned eventsel;
> >> +	unsigned cache_type;
> >> +	unsigned cache_op;
> >> +	unsigned cache_result;
> >> +} kvm_pmu_hw_cache_events[] = {
> >> +	[0] = { 0x04, PERF_COUNT_HW_CACHE_L1D, PERF_COUNT_HW_CACHE_OP_READ,
> >> +		      PERF_COUNT_HW_CACHE_RESULT_ACCESS },
> >> +	[1] = { 0x03, PERF_COUNT_HW_CACHE_L1D, PERF_COUNT_HW_CACHE_OP_READ,
> >> +		      PERF_COUNT_HW_CACHE_RESULT_MISS },
> >> +	[2] = { 0x04, PERF_COUNT_HW_CACHE_L1D, PERF_COUNT_HW_CACHE_OP_WRITE,
> >> +		      PERF_COUNT_HW_CACHE_RESULT_ACCESS },
> >> +	[3] = { 0x03, PERF_COUNT_HW_CACHE_L1D, PERF_COUNT_HW_CACHE_OP_WRITE,
> >> +		      PERF_COUNT_HW_CACHE_RESULT_MISS },
> > 
> > seems to me that the four entries above will never be used, because
> > you'll always match them in kvm_pmu_hw_events above?
> > 
> 
> Yes, I found this before, but for the completeness I list them.
> 

hmm, having unused entries for completeness is a bit weird, IMHO.
Either way, a comment explaining why they're missing or that some are
never used would be helpful.

> > Is this because perf map multiple generic perf events to the same
> > hardware event? 
> I think so.
> 
> > Does it matter if we register this with perf as one or
> > the other then?
> > 
> I think it's ok because the hardware event numbers are same.
> 

ok

> 
> >> +	[4] = { 0x12, PERF_COUNT_HW_CACHE_BPU, PERF_COUNT_HW_CACHE_OP_READ,
> >> +		      PERF_COUNT_HW_CACHE_RESULT_ACCESS },
> >> +	[5] = { 0x10, PERF_COUNT_HW_CACHE_BPU, PERF_COUNT_HW_CACHE_OP_READ,
> >> +		      PERF_COUNT_HW_CACHE_RESULT_MISS },
> >> +	[6] = { 0x12, PERF_COUNT_HW_CACHE_BPU, PERF_COUNT_HW_CACHE_OP_WRITE,
> >> +		      PERF_COUNT_HW_CACHE_RESULT_ACCESS },
> >> +	[7] = { 0x10, PERF_COUNT_HW_CACHE_BPU, PERF_COUNT_HW_CACHE_OP_WRITE,
> >> +		      PERF_COUNT_HW_CACHE_RESULT_MISS },
> >> +};
> >> +
> >> +/**
> >> + * kvm_pmu_stop_counter - stop PMU counter for the selected counter
> >> + * @vcpu: The vcpu pointer
> >> + * @select_idx: The counter index
> >> + *
> >> + * If this counter has been configured to monitor some event, disable and
> >> + * release it.
> >> + */
> >> +static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu,
> >> +				 unsigned long select_idx)
> >> +{
> >> +	struct kvm_pmu *pmu = &vcpu->arch.pmu;
> >> +	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
> >> +
> >> +	if (pmc->perf_event) {
> >> +		perf_event_disable(pmc->perf_event);
> >> +		perf_event_release_kernel(pmc->perf_event);
> >> +	}
> >> +	pmc->perf_event = NULL;
> >> +	pmc->eventsel = 0xff;
> > 
> > why is 0xff 'unused' or reserved?  If we're choosing this arbitrarily,
> > why is it not 0x3ff?  Should we create a define for this?
> > 
> 
> Yeah, 0x3ff may be better.
> 
> >> +}
> >> +
> >>  /**
> >>   * kvm_pmu_vcpu_reset - reset pmu state for cpu
> >>   * @vcpu: The vcpu pointer
> >> @@ -27,12 +87,125 @@
> >>   */
> >>  void kvm_pmu_vcpu_reset(struct kvm_vcpu *vcpu)
> >>  {
> >> +	int i;
> >>  	struct kvm_pmu *pmu = &vcpu->arch.pmu;
> >>  
> >> +	for (i = 0; i < ARMV8_MAX_COUNTERS; i++)
> >> +		kvm_pmu_stop_counter(vcpu, i);
> >> +	pmu->overflow_status = 0;
> >>  	pmu->irq_pending = false;
> >>  }
> >>  
> >>  /**
> >> + * kvm_pmu_find_hw_event - find hardware event
> >> + * @pmu: The pmu pointer
> >> + * @event_select: The number of selected event type
> >> + *
> >> + * Based on the number of selected event type, find out whether it belongs to
> >> + * PERF_TYPE_HARDWARE. If so, return the corresponding event id.
> >> + */
> >> +static unsigned kvm_pmu_find_hw_event(struct kvm_pmu *pmu,
> >> +				      unsigned long event_select)
> >> +{
> >> +	int i;
> >> +
> >> +	for (i = 0; i < ARRAY_SIZE(kvm_pmu_hw_events); i++)
> >> +		if (kvm_pmu_hw_events[i].eventsel == event_select)
> >> +			break;
> >> +
> >> +	if (i == ARRAY_SIZE(kvm_pmu_hw_events))
> >> +		return PERF_COUNT_HW_MAX;
> >> +
> >> +	return kvm_pmu_hw_events[i].event_type;
> > 
> > you can just return this directly in the loop if you have a match and
> > unconditionally return PERF_COUNT_HW_MAX outside the loop without having
> > to check the loop condition.
> > 
> ok
> >> +}
> >> +
> >> +/**
> >> + * kvm_pmu_find_hw_cache_event - find hardware cache event
> >> + * @pmu: The pmu pointer
> >> + * @event_select: The number of selected event type
> >> + *
> >> + * Based on the number of selected event type, find out whether it belongs to
> >> + * PERF_TYPE_HW_CACHE. If so, return the corresponding event id.
> >> + */
> >> +static unsigned kvm_pmu_find_hw_cache_event(struct kvm_pmu *pmu,
> >> +					    unsigned long event_select)
> >> +{
> >> +	int i;
> >> +	unsigned config;
> >> +
> >> +	for (i = 0; i < ARRAY_SIZE(kvm_pmu_hw_cache_events); i++)
> >> +		if (kvm_pmu_hw_cache_events[i].eventsel == event_select)
> >> +			break;
> >> +
> >> +	if (i == ARRAY_SIZE(kvm_pmu_hw_cache_events))
> >> +		return PERF_COUNT_HW_CACHE_MAX;
> > 
> > I feel like I just read this code, can we reuse it with a pointer to the
> > array?
> > 
> >> +
> >> +	config = (kvm_pmu_hw_cache_events[i].cache_type & 0xff)
> >> +		 | ((kvm_pmu_hw_cache_events[i].cache_op & 0xff) << 8)
> >> +		 | ((kvm_pmu_hw_cache_events[i].cache_result & 0xff) << 16);
> >> +
> >> +	return config;
> >> +}
> >> +
> >> +/**
> >> + * kvm_pmu_set_counter_event_type - set selected counter to monitor some event
> >> + * @vcpu: The vcpu pointer
> >> + * @data: The data guest writes to PMXEVTYPER_EL0
> >> + * @select_idx: The number of selected counter
> >> + *
> >> + * Firstly check whether the event type is same with the one to be set.
> >> + * If not, stop counter to monitor current event and find the event type map id.
> >> + * According to the bits of data to configure this perf_event attr and set
> >> + * exclude_host to 1 for guest. Then call perf_event API to create the
> >> + * corresponding event and save the event pointer.
> > 
> > This text seems to be describing more how the function does something,
> > as opposed to what it does and why.  I found it a little hard to read.
> > 
> >> + */
> >> +void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, unsigned long data,
> >> +				    unsigned long select_idx)
> >> +{
> >> +	struct kvm_pmu *pmu = &vcpu->arch.pmu;
> >> +	struct kvm_pmc *pmc = &pmu->pmc[select_idx];
> >> +	struct perf_event *event;
> >> +	struct perf_event_attr attr;
> >> +	unsigned config, type = PERF_TYPE_RAW;
> >> +
> >> +	if ((data & ARMV8_EVTYPE_EVENT) == pmc->eventsel)
> >> +		return;
> >> +
> >> +	kvm_pmu_stop_counter(vcpu, select_idx);
> >> +	pmc->eventsel = data & ARMV8_EVTYPE_EVENT;
> >> +
> >> +	config = kvm_pmu_find_hw_event(pmu, pmc->eventsel);
> >> +	if (config != PERF_COUNT_HW_MAX) {
> >> +		type = PERF_TYPE_HARDWARE;
> >> +	} else {
> >> +		config = kvm_pmu_find_hw_cache_event(pmu, pmc->eventsel);
> >> +		if (config != PERF_COUNT_HW_CACHE_MAX)
> >> +			type = PERF_TYPE_HW_CACHE;
> >> +	}
> >> +
> >> +	if (type == PERF_TYPE_RAW)
> >> +		config = pmc->eventsel;
> > 
> > don't you need to memset attr to 0 first?
> > 
> ok
> > otherwise, how do you ensure that for example exclude_guest is always
> > clear?
> > 
> >> +
> >> +	attr.type = type;
> >> +	attr.size = sizeof(attr);
> >> +	attr.pinned = true;
> >> +	attr.exclude_user = data & ARMV8_EXCLUDE_EL0 ? 1 : 0;
> >> +	attr.exclude_kernel = data & ARMV8_EXCLUDE_EL1 ? 1 : 0;
> >> +	attr.exclude_hv = data & ARMV8_INCLUDE_EL2 ? 0 : 1;
> > 
> > should the guest be able to see something counted in the hypervisor ever
> > or should that only be the host being able to see that?
> > 
> > my gut feeling is that the hypervisor should be hidden from the guest
> > and that exclude_hv = 0, is the right choice.  But this is a question
> > about the semantics of perf, I suppose.
> > 
> 
> This is what I'm not sure. I just thought about if guest has complete
> ELs(EL3-EL0) and how to deal with nested virtualization.
> 

nested virtualization is really not very likely to happen on arm64.  I
think the right way to look at this is that we're emulating a platform
without EL2 and therefore the guest should not see any events from EL2.

> >> +	attr.exclude_host = 1;
> >> +	attr.config = config;
> >> +	attr.sample_period = (-pmc->counter) & (((u64)1 << 32) - 1);
> > 
> > whoa, what is this scary calculation?
> > 
> > definitely needs an explanation?
> > 
> >> +
> >> +	event = perf_event_create_kernel_counter(&attr, -1, current, NULL, pmc);
> >> +	if (IS_ERR(event)) {
> >> +		kvm_err("kvm: pmu event creation failed %ld\n",
> >> +			  PTR_ERR(event));
> > 
> > doesn't this mean we'll spam the kernel log if the guest supplies
> > bogus/unsupported event numbers?
> > 
> 
> X86 uses printk_once, is that ok to us here?

yeah, that should be fine.

> 
> > In that case it shoudl be kvm_debug and the guest should be able to see
> > this somehow (e.g. events don't count).
> > 
> 
> Yes, will think about this.
> 

printk_once of kvm_debug would be fine.

Thanks,
-Christoffer