KVM: x86: do not allow re-enabling quirks

JIRA: https://issues.redhat.com/browse/RHEL-47242

commit 9966b78
Author: Paolo Bonzini <pbonzini@redhat.com>
Date:   Mon Mar 3 09:09:37 2025 -0500

    KVM: x86: do not allow re-enabling quirks

    Allowing arbitrary re-enabling of quirks puts a limit on what the
    quirks themselves can do, since you cannot assume that the quirk
    prevents a particular state.  More important, it also prevents
    KVM from disabling a quirk at VM creation time, because userspace
    can always go back and re-enable that.

    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>

Author: Maxim Levitsky

arch/x86/kvm/x86.c

@@ -6550,7 +6550,7 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 			break;
 		fallthrough;
 	case KVM_CAP_DISABLE_QUIRKS:
-		kvm->arch.disabled_quirks = cap->args[0];
+		kvm->arch.disabled_quirks |= cap->args[0];
 		r = 0;
 		break;
 	case KVM_CAP_SPLIT_IRQCHIP: {