[PATCH v10 020/108] KVM: Support KVM_CAP_MAX_VCPUS for KVM_ENABLE_CAP

[isaku . yamahata]

From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

TDX attestation includes the maximum number of vcpu that the guest can
accommodate.  For that, the maximum number of vcpu needs to be specified
instead of constant, KVM_MAX_VCPUS.  Make KVM_ENABLE_CAP support
KVM_CAP_MAX_VCPUS.

Suggested-by: Sagi Shahar <sagis@xxxxxxxxxx>
Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
---
 virt/kvm/kvm_main.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b9c270f97c88..3b05a3396f89 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4967,6 +4967,27 @@ static int kvm_vm_ioctl_enable_cap_generic(struct kvm *kvm,
 	case KVM_CAP_DIRTY_LOG_RING:
 	case KVM_CAP_DIRTY_LOG_RING_ACQ_REL:
 		return kvm_vm_ioctl_enable_dirty_log_ring(kvm, cap->args[0]);
+	case KVM_CAP_MAX_VCPUS: {
+		int r;
+
+		if (cap->flags || cap->args[0] == 0)
+			return -EINVAL;
+		if (cap->args[0] >  kvm_vm_ioctl_check_extension(kvm, KVM_CAP_MAX_VCPUS))
+			return -E2BIG;
+
+		mutex_lock(&kvm->lock);
+		/* Only decreasing is allowed. */
+		if (cap->args[0] > kvm->max_vcpus)
+			r = -E2BIG;
+		else if (kvm->created_vcpus)
+			r = -EBUSY;
+		else {
+			kvm->max_vcpus = cap->args[0];
+			r = 0;
+		}
+		mutex_unlock(&kvm->lock);
+		return r;
+	}
 	default:
 		return kvm_vm_ioctl_enable_cap(kvm, cap);
 	}
-- 
2.25.1