[PATCH] LoongArch: KVM: Advertise already-supported capabilities

[Tao Cui <cui.tao@linux.dev>]

Several LoongArch KVM features are fully implemented but were never
reported through their standard KVM_CHECK_EXTENSION probes, so userspace
cannot discover them and either ignores them or takes a slower path.
Advertise the ones that already work:

  - KVM_CAP_STEAL_TIME: steal time is fully implemented (host-side
    record plus guest paravirt), gated on kvm_pvtime_supported().

  - KVM_CAP_IRQFD_RESAMPLE: the resampler is generic code backed by the
    in-kernel irqchip; advertise it so userspace can use irqfd with
    resample for level-triggered interrupts.

  - KVM_CAP_VM_GPA_BITS: the guest physical address width is already
    computed as BIT(cpu_vabits), so return cpu_vabits directly.

  - KVM_CAP_VCPU_ATTRIBUTES: per-vCPU device-attribute ioctls are
    implemented (CPUCFG, PVTIME control); advertise the discovery cap.

This adds no new functionality; it only makes existing features
discoverable via the standard probe.

Signed-off-by: Tao Cui <cui.tao@linux.dev>
---
 arch/loongarch/kvm/vm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
index 1317c718f896..d7dd08d9be5b 100644
--- a/arch/loongarch/kvm/vm.c
+++ b/arch/loongarch/kvm/vm.c
@@ -120,8 +120,10 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_READONLY_MEM:
 	case KVM_CAP_IMMEDIATE_EXIT:
 	case KVM_CAP_IOEVENTFD:
+	case KVM_CAP_IRQFD_RESAMPLE:
 	case KVM_CAP_MP_STATE:
 	case KVM_CAP_SET_GUEST_DEBUG:
+	case KVM_CAP_VCPU_ATTRIBUTES:
 		r = 1;
 		break;
 	case KVM_CAP_NR_VCPUS:
@@ -136,6 +138,12 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_NR_MEMSLOTS:
 		r = KVM_USER_MEM_SLOTS;
 		break;
+	case KVM_CAP_STEAL_TIME:
+		r = kvm_pvtime_supported();
+		break;
+	case KVM_CAP_VM_GPA_BITS:
+		r = cpu_vabits;
+		break;
 	default:
 		r = 0;
 		break;