Commit b7628c79 authored by Marc Zyngier's avatar Marc Zyngier
Browse files

KVM: arm64: Allow userspace to limit the number of PMU counters for EL2 VMs 



As long as we had purely EL1 VMs, we could easily update the number
of guest-visible counters by letting userspace write to PMCR_EL0.N.

With VMs started at EL2, PMCR_EL1.N only reflects MDCR_EL2.HPMN,
and we don't have a good way to limit it.

For this purpose, introduce a new PMUv3 attribute that allows
limiting the maximum number of counters. This requires the explicit
selection of a PMU.

Suggested-by: default avatarOliver Upton <oliver.upton@linux.dev>
Reviewed-by: default avatarOliver Upton <oliver.upton@linux.dev>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
parent 02243533

Documentation/virt/kvm/devices/vcpu.rst

+24 −0
Original line number Diff line number Diff line
@@ -137,6 +137,30 @@ exit_reason = KVM_EXIT_FAIL_ENTRY and populate the fail_entry struct by setting 
hardare_entry_failure_reason field to KVM_EXIT_FAIL_ENTRY_CPU_UNSUPPORTED and

the cpu field to the processor id.



1.5 ATTRIBUTE: KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS

--------------------------------------------------



:Parameters: in kvm_device_attr.addr the address to an unsigned int

	     representing the maximum value taken by PMCR_EL0.N



:Returns:



	 =======  ====================================================

	 -EBUSY   PMUv3 already initialized, a VCPU has already run or

                  an event filter has already been set

	 -EFAULT  Error accessing the value pointed to by addr

	 -ENODEV  PMUv3 not supported or GIC not initialized

	 -EINVAL  No PMUv3 explicitly selected, or value of N out of

	 	  range

	 =======  ====================================================



Set the number of implemented event counters in the virtual PMU. This

mandates that a PMU has explicitly been selected via

KVM_ARM_VCPU_PMU_V3_SET_PMU, and will fail when no PMU has been

explicitly selected, or the number of counters is out of range for the

selected PMU. Selecting a new PMU cancels the effect of setting this

attribute.



2. GROUP: KVM_ARM_VCPU_TIMER_CTRL

=================================

arch/arm64/include/uapi/asm/kvm.h

+5 −4
Original line number Diff line number Diff line
@@ -435,6 +435,7 @@ enum { 
#define   KVM_ARM_VCPU_PMU_V3_INIT		1

#define   KVM_ARM_VCPU_PMU_V3_FILTER		2

#define   KVM_ARM_VCPU_PMU_V3_SET_PMU		3

#define   KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS	4

#define KVM_ARM_VCPU_TIMER_CTRL		1

#define   KVM_ARM_VCPU_TIMER_IRQ_VTIMER		0

#define   KVM_ARM_VCPU_TIMER_IRQ_PTIMER		1

arch/arm64/kvm/pmu-emul.c

+24 −0
Original line number Diff line number Diff line
@@ -1104,6 +1104,20 @@ static int kvm_arm_pmu_v3_set_pmu(struct kvm_vcpu *vcpu, int pmu_id) 
	return ret;

}



static int kvm_arm_pmu_v3_set_nr_counters(struct kvm_vcpu *vcpu, unsigned int n)

{

	struct kvm *kvm = vcpu->kvm;



	if (!kvm->arch.arm_pmu)

		return -EINVAL;



	if (n > kvm_arm_pmu_get_max_counters(kvm))

		return -EINVAL;



	kvm_arm_set_nr_counters(kvm, n);

	return 0;

}



int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)

{

	struct kvm *kvm = vcpu->kvm;
@@ -1200,6 +1214,15 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr) 


		return kvm_arm_pmu_v3_set_pmu(vcpu, pmu_id);

	}

	case KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS: {

		unsigned int __user *uaddr = (unsigned int __user *)(long)attr->addr;

		unsigned int n;



		if (get_user(n, uaddr))

			return -EFAULT;



		return kvm_arm_pmu_v3_set_nr_counters(vcpu, n);

	}

	case KVM_ARM_VCPU_PMU_V3_INIT:

		return kvm_arm_pmu_v3_init(vcpu);

	}
@@ -1238,6 +1261,7 @@ int kvm_arm_pmu_v3_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr) 
	case KVM_ARM_VCPU_PMU_V3_INIT:

	case KVM_ARM_VCPU_PMU_V3_FILTER:

	case KVM_ARM_VCPU_PMU_V3_SET_PMU:

	case KVM_ARM_VCPU_PMU_V3_SET_NR_COUNTERS:

		if (kvm_vcpu_has_pmu(vcpu))

			return 0;

	}