[PATCH v2] 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.  Advertise the ones that already work and have a
real consumer:

  - KVM_CAP_STEAL_TIME: steal time works end-to-end (host-side record
    plus guest paravirt side), and the probe returns kvm_pvtime_supported().

  - 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>
---
Changes in v2:
  - Drop KVM_CAP_IRQFD_RESAMPLE: the only consumer is VFIO INTx, which
    needs IOMMU/VFIO not yet available on LoongArch.
  - Drop KVM_CAP_VM_GPA_BITS: the cap implies a GPA-width setter that
    LoongArch does not implement.

 arch/loongarch/kvm/vm.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
index 1317c718f896..0a51931d6f6e 100644
--- a/arch/loongarch/kvm/vm.c
+++ b/arch/loongarch/kvm/vm.c
@@ -122,6 +122,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_IOEVENTFD:
 	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 +137,9 @@ 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;
 	default:
 		r = 0;
 		break;