Re: [PATCH v7 19/19] KVM: ARM64: Add a new kvm ARM PMU device

[Marc Zyngier <marc.zyngier@arm.com>]

On 15/12/15 15:50, Shannon Zhao wrote:
> 
> 
> On 2015/12/15 23:33, Marc Zyngier wrote:
>> On 15/12/15 08:49, Shannon Zhao wrote:
>>>> From: Shannon Zhao<shannon.zhao@linaro.org>
>>>>
>>>> Add a new kvm device type KVM_DEV_TYPE_ARM_PMU_V3 for ARM PMU. Implement
>>>> the kvm_device_ops for it.
>>>>
>>>> Signed-off-by: Shannon Zhao<shannon.zhao@linaro.org>
>>>> ---
>>>>  Documentation/virtual/kvm/devices/arm-pmu.txt |  16 ++++
>>>>  arch/arm64/include/uapi/asm/kvm.h             |   3 +
>>>>  include/linux/kvm_host.h                      |   1 +
>>>>  include/uapi/linux/kvm.h                      |   2 +
>>>>  virt/kvm/arm/pmu.c                            | 115 ++++++++++++++++++++++++++
>>>>  virt/kvm/kvm_main.c                           |   4 +
>>>>  6 files changed, 141 insertions(+)
>>>>  create mode 100644 Documentation/virtual/kvm/devices/arm-pmu.txt
>>>>
>>>> diff --git a/Documentation/virtual/kvm/devices/arm-pmu.txt b/Documentation/virtual/kvm/devices/arm-pmu.txt
>>>> new file mode 100644
>>>> index 0000000..5121f1f
>>>> --- /dev/null
>>>> +++ b/Documentation/virtual/kvm/devices/arm-pmu.txt
>>>> @@ -0,0 +1,16 @@
>>>> +ARM Virtual Performance Monitor Unit (vPMU)
>>>> +===========================================
>>>> +
>>>> +Device types supported:
>>>> +  KVM_DEV_TYPE_ARM_PMU_V3         ARM Performance Monitor Unit v3
>>>> +
>>>> +Instantiate one PMU instance for per VCPU through this API.
>>>> +
>>>> +Groups:
>>>> +  KVM_DEV_ARM_PMU_GRP_IRQ
>>>> +  Attributes:
>>>> +    A value describing the interrupt number of PMU overflow interrupt. This
>>>> +    interrupt should be a PPI.
>>>> +
>>>> +  Errors:
>>>> +    -EINVAL: Value set is out of the expected range (from 16 to 31)
>>>> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
>>>> index 2d4ca4b..568afa2 100644
>>>> --- a/arch/arm64/include/uapi/asm/kvm.h
>>>> +++ b/arch/arm64/include/uapi/asm/kvm.h
>>>> @@ -204,6 +204,9 @@ struct kvm_arch_memory_slot {
>>>>  #define KVM_DEV_ARM_VGIC_GRP_CTRL	4
>>>>  #define   KVM_DEV_ARM_VGIC_CTRL_INIT	0
>>>>
>>>> +/* Device Control API: ARM PMU */
>>>> +#define KVM_DEV_ARM_PMU_GRP_IRQ		0
>>>> +
>>>>  /* KVM_IRQ_LINE irq field index values */
>>>>  #define KVM_ARM_IRQ_TYPE_SHIFT		24
>>>>  #define KVM_ARM_IRQ_TYPE_MASK		0xff
>>>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>>>> index c923350..608dea6 100644
>>>> --- a/include/linux/kvm_host.h
>>>> +++ b/include/linux/kvm_host.h
>>>> @@ -1161,6 +1161,7 @@ extern struct kvm_device_ops kvm_mpic_ops;
>>>>  extern struct kvm_device_ops kvm_xics_ops;
>>>>  extern struct kvm_device_ops kvm_arm_vgic_v2_ops;
>>>>  extern struct kvm_device_ops kvm_arm_vgic_v3_ops;
>>>> +extern struct kvm_device_ops kvm_arm_pmu_ops;
>>>>
>>>>  #ifdef CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT
>>>>
>>>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>>>> index 03f3618..4ba6fdd 100644
>>>> --- a/include/uapi/linux/kvm.h
>>>> +++ b/include/uapi/linux/kvm.h
>>>> @@ -1032,6 +1032,8 @@ enum kvm_device_type {
>>>>  #define KVM_DEV_TYPE_FLIC		KVM_DEV_TYPE_FLIC
>>>>  	KVM_DEV_TYPE_ARM_VGIC_V3,
>>>>  #define KVM_DEV_TYPE_ARM_VGIC_V3	KVM_DEV_TYPE_ARM_VGIC_V3
>>>> +	KVM_DEV_TYPE_ARM_PMU_V3,
>>>> +#define	KVM_DEV_TYPE_ARM_PMU_V3		KVM_DEV_TYPE_ARM_PMU_V3
>>>>  	KVM_DEV_TYPE_MAX,
>>>>  };
>>>>
>>>> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
>>>> index d113ee4..1965d0d 100644
>>>> --- a/virt/kvm/arm/pmu.c
>>>> +++ b/virt/kvm/arm/pmu.c
>>>> @@ -19,6 +19,7 @@
>>>>  #include <linux/kvm.h>
>>>>  #include <linux/kvm_host.h>
>>>>  #include <linux/perf_event.h>
>>>> +#include <linux/uaccess.h>
>>>>  #include <asm/kvm_emulate.h>
>>>>  #include <kvm/arm_pmu.h>
>>>>  #include <kvm/arm_vgic.h>
>>>> @@ -357,3 +358,117 @@ void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data,
>>>>
>>>>  	pmc->perf_event = event;
>>>>  }
>>>> +
>>>> +static inline bool kvm_arm_pmu_initialized(struct kvm_vcpu *vcpu)
>>>> +{
>>>> +	return vcpu->arch.pmu.irq_num != -1;
>>>> +}
>>>> +
>>>> +static int kvm_arm_pmu_irq_access(struct kvm *kvm, int *irq, bool is_set)
>>>> +{
>>>> +	int j;
>>>> +	struct kvm_vcpu *vcpu;
>>>> +
>>>> +	kvm_for_each_vcpu(j, vcpu, kvm) {
>>>> +		struct kvm_pmu *pmu = &vcpu->arch.pmu;
>>>> +
>>>> +		if (!is_set) {
>>>> +			if (!kvm_arm_pmu_initialized(vcpu))
>>>> +				return -EBUSY;
>> Returning -EBUSY is a bit odd. Maybe -EINVAL? But this seems weird
>> anyway. Actually, why would you return an error in this case?
>>
> While this is a unexpected operation from user space and it's already 
> initialized and working, so I think it should return an error to user 
> and tell user that it's already initialized and working (this should 
> mean "busy" ?).

But in this case, you're returning an error if it is *not* initialized.
I understand that in that case you cannot return an interrupt number (-1
would be weird), but returning -EBUSY feels even more weird.

I'd settle for -ENOXIO, or something similar. Anyone having a better idea?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...