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

[Andrew Jones]

On Tue, Dec 15, 2015 at 03:59:31PM +0000, Marc Zyngier wrote:
> 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<address@hidden>
> >>>>
> >>>> 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<address@hidden>
> >>>> ---
> >>>>  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?

Added qemu-devel (Peter). I think for the most part QEMU just stringifies
errnos and outputs them. So, in the absence of a kernel message, having
more unique errnos does help zero-in on a problem. However EINVAL plus a
kernel message is probably even better, and it doesn't start with people
trying to understand why a particular errno (which makes about as much
sense as EINVAL, but seems to be attempting to provide something more...)
was used.

Thanks,
drew