KVM: x86/xen: Add KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID

In order to intercept hypercalls such as VCPUOP_set_singleshot_timer, we
need to be aware of the Xen CPU numbering.

This looks a lot like the Hyper-V handling of vpidx, for obvious reasons.
Signed-off-by: NDavid Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-12-dwmw2@infradead.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -613,6 +613,7 @@ struct kvm_vcpu_xen {
 	u64 runstate_entry_time;
 	u64 runstate_times[4];
 	unsigned long evtchn_pending_sel;
+	u32 vcpu_id; /* The Xen / ACPI vCPU ID */
 };
 
 struct kvm_vcpu_arch {

arch/x86/kvm/x86.c

@@ -11262,6 +11262,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 
 	vcpu->arch.arch_capabilities = kvm_get_arch_capabilities();
 	vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
+	kvm_xen_init_vcpu(vcpu);
 	kvm_vcpu_mtrr_init(vcpu);
 	vcpu_load(vcpu);
 	kvm_set_tsc_khz(vcpu, max_tsc_khz);

arch/x86/kvm/xen.c

@@ -603,6 +603,15 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
 		r = 0;
 		break;
 
+	case KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID:
+		if (data->u.vcpu_id >= KVM_MAX_VCPUS)
+			r = -EINVAL;
+		else {
+			vcpu->arch.xen.vcpu_id = data->u.vcpu_id;
+			r = 0;
+		}
+		break;
+
 	default:
 		break;
 	}
@@ -678,6 +687,11 @@ int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
 		r = -EINVAL;
 		break;
 
+	case KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID:
+		data->u.vcpu_id = vcpu->arch.xen.vcpu_id;
+		r = 0;
+		break;
+
 	default:
 		break;
 	}
@@ -1377,6 +1391,11 @@ static bool kvm_xen_hcall_evtchn_send(struct kvm_vcpu *vcpu, u64 param, u64 *r)
 	return true;
 }
 
+void kvm_xen_init_vcpu(struct kvm_vcpu *vcpu)
+{
+	vcpu->arch.xen.vcpu_id = vcpu->vcpu_idx;
+}
+
 void kvm_xen_destroy_vcpu(struct kvm_vcpu *vcpu)
 {
 	kvm_gfn_to_pfn_cache_destroy(vcpu->kvm,

arch/x86/kvm/xen.h

@@ -25,6 +25,7 @@ int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data);
 int kvm_xen_hvm_config(struct kvm *kvm, struct kvm_xen_hvm_config *xhc);
 void kvm_xen_init_vm(struct kvm *kvm);
 void kvm_xen_destroy_vm(struct kvm *kvm);
+void kvm_xen_init_vcpu(struct kvm_vcpu *vcpu);
 void kvm_xen_destroy_vcpu(struct kvm_vcpu *vcpu);
 int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe,
 			    struct kvm *kvm);
@@ -75,6 +76,10 @@ static inline void kvm_xen_destroy_vm(struct kvm *kvm)
 {
 }
 
+static inline void kvm_xen_init_vcpu(struct kvm_vcpu *vcpu)
+{
+}
+
 static inline void kvm_xen_destroy_vcpu(struct kvm_vcpu *vcpu)
 {
 }

include/uapi/linux/kvm.h

@@ -1747,6 +1747,7 @@ struct kvm_xen_vcpu_attr {
 			__u64 time_blocked;
 			__u64 time_offline;
 		} runstate;
+		__u32 vcpu_id;
 	} u;
 };
 
@@ -1757,6 +1758,8 @@ struct kvm_xen_vcpu_attr {
 #define KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_CURRENT	0x3
 #define KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_DATA	0x4
 #define KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADJUST	0x5
+/* Available with KVM_CAP_XEN_HVM / KVM_XEN_HVM_CONFIG_EVTCHN_SEND */
+#define KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID		0x6
 
 /* Secure Encrypted Virtualization command */
 enum sev_cmd_id {