Re: [RFC v2 PATCH 3/7] KVM: arm/arm64: Register perf trace event notifier

[Punit Agrawal]

Christoffer Dall <christoffer.dall@xxxxxxxxxx> writes:

> On Mon, Sep 05, 2016 at 05:31:33PM +0100, Punit Agrawal wrote:
>> Register a notifier to track state changes of perf trace events.
>> 
>> The notifier will enable taking appropriate action for trace events
>> targeting VM.
>> 
>> Signed-off-by: Punit Agrawal <punit.agrawal@xxxxxxx>
>> Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
>> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
>
> Overall this looks reasonable, but I'm wondering if most if this logic
> should really go in virt/kvm/perf_trace.c and call into arch-specific
> hooks, similar to the way it works for preempt notifiers.
>
> On the other hand, if arm/arm64 are the only two architectures that are
> going to use this, creating stubs for the other architectures could be a
> bit tedious.

If the series looks to be headed in the right direction, I'll be adding
support for 32bit ARM host as well.

Most of the code here can be shared between arm and arm64. At that
point, it might be worth moving the logic here to a commong location
with the architecture code responsible for registering it's
kvm_trace_hooks as part of the initialisation (or something along those
lines).

I'll wait a bit for maintainer feedback on Patch 1 before re-spinning the
series. Patch 1 ultimately decides what the user facing interface for
this functionality looks like.

Thanks for your feedback on the series.

Punit

>
> Thanks,
> -Christoffer
>
>> ---
>>  arch/arm/include/asm/kvm_host.h   |   3 +
>>  arch/arm/kvm/arm.c                |   2 +
>>  arch/arm64/include/asm/kvm_host.h |   8 +++
>>  arch/arm64/kvm/Kconfig            |   4 ++
>>  arch/arm64/kvm/Makefile           |   1 +
>>  arch/arm64/kvm/perf_trace.c       | 122 ++++++++++++++++++++++++++++++++++++++
>>  6 files changed, 140 insertions(+)
>>  create mode 100644 arch/arm64/kvm/perf_trace.c
>> 
>> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
>> index de338d9..609998e 100644
>> --- a/arch/arm/include/asm/kvm_host.h
>> +++ b/arch/arm/include/asm/kvm_host.h
>> @@ -280,6 +280,9 @@ static inline int kvm_arch_dev_ioctl_check_extension(struct kvm *kvm, long ext)
>>  int kvm_perf_init(void);
>>  int kvm_perf_teardown(void);
>>  
>> +static inline int kvm_perf_trace_init(void) { return 0; }
>> +static inline int kvm_perf_trace_teardown(void) { return 0; }
>> +
>>  void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
>>  
>>  struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>> index 75f130e..e1b99c4 100644
>> --- a/arch/arm/kvm/arm.c
>> +++ b/arch/arm/kvm/arm.c
>> @@ -1220,6 +1220,7 @@ static int init_subsystems(void)
>>  		goto out;
>>  
>>  	kvm_perf_init();
>> +	kvm_perf_trace_init();
>>  	kvm_coproc_table_init();
>>  
>>  out:
>> @@ -1411,6 +1412,7 @@ out_err:
>>  void kvm_arch_exit(void)
>>  {
>>  	kvm_perf_teardown();
>> +	kvm_perf_trace_teardown();
>>  }
>>  
>>  static int arm_init(void)
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index 3eda975..f6ff8e5 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -345,6 +345,14 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
>>  int kvm_perf_init(void);
>>  int kvm_perf_teardown(void);
>>  
>> +#if !defined(CONFIG_KVM_PERF_TRACE)
>> +static inline int kvm_perf_trace_init(void) { return 0; }
>> +static inline int kvm_perf_trace_teardown(void) { return 0; }
>> +#else
>> +int kvm_perf_trace_init(void);
>> +int kvm_perf_trace_teardown(void);
>> +#endif
>> +
>>  struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
>>  
>>  static inline void __cpu_init_hyp_mode(phys_addr_t pgd_ptr,
>> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
>> index 9c9edc9..56e9537 100644
>> --- a/arch/arm64/kvm/Kconfig
>> +++ b/arch/arm64/kvm/Kconfig
>> @@ -19,6 +19,9 @@ if VIRTUALIZATION
>>  config KVM_ARM_VGIC_V3
>>  	bool
>>  
>> +config KVM_PERF_TRACE
>> +        bool
>> +
>>  config KVM
>>  	bool "Kernel-based Virtual Machine (KVM) support"
>>  	depends on OF
>> @@ -39,6 +42,7 @@ config KVM
>>  	select HAVE_KVM_MSI
>>  	select HAVE_KVM_IRQCHIP
>>  	select HAVE_KVM_IRQ_ROUTING
>> +	select KVM_PERF_TRACE if EVENT_TRACING && PERF_EVENTS
>>  	---help---
>>  	  Support hosting virtualized guest machines.
>>  	  We don't support KVM with 16K page tables yet, due to the multiple
>> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
>> index 695eb3c..7d175e4 100644
>> --- a/arch/arm64/kvm/Makefile
>> +++ b/arch/arm64/kvm/Makefile
>> @@ -19,6 +19,7 @@ kvm-$(CONFIG_KVM_ARM_HOST) += $(ARM)/psci.o $(ARM)/perf.o
>>  kvm-$(CONFIG_KVM_ARM_HOST) += emulate.o inject_fault.o regmap.o
>>  kvm-$(CONFIG_KVM_ARM_HOST) += hyp.o hyp-init.o handle_exit.o
>>  kvm-$(CONFIG_KVM_ARM_HOST) += guest.o debug.o reset.o sys_regs.o sys_regs_generic_v8.o
>> +kvm-$(CONFIG_KVM_PERF_TRACE) += perf_trace.o
>>  
>>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/vgic/vgic.o
>>  kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/vgic/vgic-init.o
>> diff --git a/arch/arm64/kvm/perf_trace.c b/arch/arm64/kvm/perf_trace.c
>> new file mode 100644
>> index 0000000..8bacd18
>> --- /dev/null
>> +++ b/arch/arm64/kvm/perf_trace.c
>> @@ -0,0 +1,122 @@
>> +/*
>> + * Copyright (C) 2016 ARM Ltd.
>> + * Author: Punit Agrawal <punit.agrawal@xxxxxxx>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> + * GNU General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU General Public License
>> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
>> + */
>> +#include <linux/kvm_host.h>
>> +#include <linux/trace_events.h>
>> +
>> +typedef int (*perf_trace_callback_fn)(struct kvm *kvm, bool enable);
>> +
>> +struct kvm_trace_hook {
>> +	char *key;
>> +	perf_trace_callback_fn setup_fn;
>> +};
>> +
>> +static struct kvm_trace_hook trace_hook[] = {
>> +	{ },
>> +};
>> +
>> +static perf_trace_callback_fn find_trace_callback(const char *trace_key)
>> +{
>> +	int i;
>> +
>> +	for (i = 0; trace_hook[i].key; i++)
>> +		if (!strcmp(trace_key, trace_hook[i].key))
>> +			return trace_hook[i].setup_fn;
>> +
>> +	return NULL;
>> +}
>> +
>> +static int kvm_perf_trace_notifier(struct notifier_block *nb,
>> +				   unsigned long event, void *data)
>> +{
>> +	struct perf_event *p_event = data;
>> +	struct trace_event_call *tp_event = p_event->tp_event;
>> +	perf_trace_callback_fn setup_trace_fn;
>> +	struct kvm *kvm = NULL;
>> +	struct pid *pid;
>> +	bool found = false;
>> +
>> +	/*
>> +	 * Is this a trace point?
>> +	 */
>> +	if (!(tp_event->flags & TRACE_EVENT_FL_TRACEPOINT))
>> +		goto out;
>> +
>> +	/*
>> +	 * We'll get here for events we care to monitor for KVM. As we
>> +	 * only care about events attached to a VM, check that there
>> +	 * is a task associated with the perf event.
>> +	 */
>> +	if (p_event->attach_state != PERF_ATTACH_TASK)
>> +		goto out;
>> +
>> +	/*
>> +	 * This notifier gets called when perf trace event instance is
>> +	 * added or removed. Until we can restrict this to events of
>> +	 * interest in core, minimise the overhead below.
>> +	 *
>> +	 * Do we care about it? i.e., is there a callback for this
>> +	 * trace point?
>> +	 */
>> +	setup_trace_fn = find_trace_callback(tp_event->tp->name);
>> +	if (!setup_trace_fn)
>> +		goto out;
>> +
>> +	pid = get_task_pid(p_event->hw.target, PIDTYPE_PID);
>> +
>> +	/*
>> +	 * Does it match any of the VMs?
>> +	 */
>> +	spin_lock(&kvm_lock);
>> +	list_for_each_entry(kvm, &vm_list, vm_list) {
>> +		if (kvm->pid == pid) {
>> +			found = true;
>> +			break;
>> +		}
>> +	}
>> +	spin_unlock(&kvm_lock);
>> +
>> +	put_pid(pid);
>> +	if (!found)
>> +		goto out;
>> +
>> +	switch (event) {
>> +	case TRACE_REG_PERF_OPEN:
>> +		setup_trace_fn(kvm, true);
>> +		break;
>> +
>> +	case TRACE_REG_PERF_CLOSE:
>> +		setup_trace_fn(kvm, false);
>> +		break;
>> +	}
>> +
>> +out:
>> +	return 0;
>> +}
>> +
>> +static struct notifier_block kvm_perf_trace_notifier_block = {
>> +	.notifier_call = kvm_perf_trace_notifier,
>> +};
>> +
>> +int kvm_perf_trace_init(void)
>> +{
>> +	return perf_trace_notifier_register(&kvm_perf_trace_notifier_block);
>> +}
>> +
>> +int kvm_perf_trace_teardown(void)
>> +{
>> +	return perf_trace_notifier_unregister(&kvm_perf_trace_notifier_block);
>> +}
>> -- 
>> 2.8.1
>> 
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