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arm64/x86: KVM: Introduce steal-time cap

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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: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://lore.kernel.org/r/20200804170604.42662-7-drjones@redhat.com
This commit is contained in:
Andrew Jones 2020-08-04 19:06:04 +02:00 committed by Marc Zyngier
parent 739c7af7da
commit 004a01241c
6 changed files with 22 additions and 1 deletions
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13
Documentation/virt/kvm/api.rst
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@ -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".

1
arch/arm64/include/asm/kvm_host.h
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@ -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,

3
arch/arm64/kvm/arm.c
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@ -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;

2
arch/arm64/kvm/pvtime.c
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@ -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();
}

3
arch/x86/kvm/x86.c
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@ -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;
}

1
include/uapi/linux/kvm.h
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@ -1035,6 +1035,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_LAST_CPU 184
#define KVM_CAP_SMALLER_MAXPHYADDR 185
#define KVM_CAP_S390_DIAG318 186
#define KVM_CAP_STEAL_TIME 187
#ifdef KVM_CAP_IRQ_ROUTING