Commit 004a0124 authored by Andrew Jones's avatar Andrew Jones Committed by Marc Zyngier
Browse files

arm64/x86: KVM: Introduce steal-time cap 



arm64 requires a vcpu fd (KVM_HAS_DEVICE_ATTR vcpu ioctl) to probe
support for steal-time. However this is unnecessary, as only a KVM
fd is required, and it complicates userspace (userspace may prefer
delaying vcpu creation until after feature probing). Introduce a cap
that can be checked instead. While x86 can already probe steal-time
support with a kvm fd (KVM_GET_SUPPORTED_CPUID), we add the cap there
too for consistency.

Signed-off-by: default avatarAndrew Jones <drjones@redhat.com>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Reviewed-by: default avatarSteven Price <steven.price@arm.com>
Link: https://lore.kernel.org/r/20200804170604.42662-7-drjones@redhat.com
parent 739c7af7

Documentation/virt/kvm/api.rst

+13 −0
Original line number Diff line number Diff line
@@ -6160,3 +6160,16 @@ KVM can therefore start protected VMs. 
This capability governs the KVM_S390_PV_COMMAND ioctl and the

KVM_MP_STATE_LOAD MP_STATE. KVM_SET_MP_STATE can fail for protected

guests when the state change is invalid.



8.24 KVM_CAP_STEAL_TIME

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



:Architectures: arm64, x86



This capability indicates that KVM supports steal time accounting.

When steal time accounting is supported it may be enabled with

architecture-specific interfaces.  This capability and the architecture-

specific interfaces must be consistent, i.e. if one says the feature

is supported, than the other should as well and vice versa.  For arm64

see Documentation/virt/kvm/devices/vcpu.rst "KVM_ARM_VCPU_PVTIME_CTRL".

For x86 see Documentation/virt/kvm/msr.rst "MSR_KVM_STEAL_TIME".

arch/arm64/include/asm/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -543,6 +543,7 @@ long kvm_hypercall_pv_features(struct kvm_vcpu *vcpu); 
gpa_t kvm_init_stolen_time(struct kvm_vcpu *vcpu);

void kvm_update_stolen_time(struct kvm_vcpu *vcpu);



bool kvm_arm_pvtime_supported(void);

int kvm_arm_pvtime_set_attr(struct kvm_vcpu *vcpu,

			    struct kvm_device_attr *attr);

int kvm_arm_pvtime_get_attr(struct kvm_vcpu *vcpu,

arch/arm64/kvm/arm.c

+3 −0
Original line number Diff line number Diff line
@@ -206,6 +206,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) 
		 */

		r = 1;

		break;

	case KVM_CAP_STEAL_TIME:

		r = kvm_arm_pvtime_supported();

		break;

	default:

		r = kvm_arch_vm_ioctl_check_extension(kvm, ext);

		break;

arch/arm64/kvm/pvtime.c

+1 −1
Original line number Diff line number Diff line
@@ -71,7 +71,7 @@ gpa_t kvm_init_stolen_time(struct kvm_vcpu *vcpu) 
	return base;

}



static bool kvm_arm_pvtime_supported(void)

bool kvm_arm_pvtime_supported(void)

{

	return !!sched_info_on();

}

arch/x86/kvm/x86.c

+3 −0
Original line number Diff line number Diff line
@@ -3581,6 +3581,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) 
	case KVM_CAP_SMALLER_MAXPHYADDR:

		r = (int) allow_smaller_maxphyaddr;

		break;

	case KVM_CAP_STEAL_TIME:

		r = sched_info_on();

		break;

	default:

		break;

	}

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