svm: Introduces AVIC per-VM ID

Introduces per-VM AVIC ID and helper functions to manage the IDs.
Currently, the ID will be used to implement 32-bit AVIC IOMMU GA tag.

The ID is 24-bit one-based indexing value, and is managed via helper
functions to get the next ID, or to free an ID once a VM is destroyed.
There should be no ID conflict for any active VMs.

Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -781,6 +781,7 @@ struct kvm_arch {
 	bool disabled_lapic_found;
 
 	/* Struct members for AVIC */
+	u32 avic_vm_id;
 	u32 ldr_mode;
 	struct page *avic_logical_id_table_page;
 	struct page *avic_physical_id_table_page;

arch/x86/kvm/svm.c

@@ -96,6 +96,19 @@ MODULE_DEVICE_TABLE(x86cpu, svm_cpu_id);
 #define AVIC_UNACCEL_ACCESS_OFFSET_MASK		0xFF0
 #define AVIC_UNACCEL_ACCESS_VECTOR_MASK		0xFFFFFFFF
 
+/* AVIC GATAG is encoded using VM and VCPU IDs */
+#define AVIC_VCPU_ID_BITS		8
+#define AVIC_VCPU_ID_MASK		((1 << AVIC_VCPU_ID_BITS) - 1)
+
+#define AVIC_VM_ID_BITS			24
+#define AVIC_VM_ID_NR			(1 << AVIC_VM_ID_BITS)
+#define AVIC_VM_ID_MASK			((1 << AVIC_VM_ID_BITS) - 1)
+
+#define AVIC_GATAG(x, y)		(((x & AVIC_VM_ID_MASK) << AVIC_VCPU_ID_BITS) | \
+						(y & AVIC_VCPU_ID_MASK))
+#define AVIC_GATAG_TO_VMID(x)		((x >> AVIC_VCPU_ID_BITS) & AVIC_VM_ID_MASK)
+#define AVIC_GATAG_TO_VCPUID(x)		(x & AVIC_VCPU_ID_MASK)
+
 static bool erratum_383_found __read_mostly;
 
 static const u32 host_save_user_msrs[] = {
@@ -242,6 +255,10 @@ static int avic;
 module_param(avic, int, S_IRUGO);
 #endif
 
+/* AVIC VM ID bit masks and lock */
+static DECLARE_BITMAP(avic_vm_id_bitmap, AVIC_VM_ID_NR);
+static DEFINE_SPINLOCK(avic_vm_id_lock);
+
 static void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
 static void svm_flush_tlb(struct kvm_vcpu *vcpu);
 static void svm_complete_interrupts(struct vcpu_svm *svm);
@@ -1280,10 +1297,40 @@ static int avic_init_backing_page(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
+static inline int avic_get_next_vm_id(void)
+{
+	int id;
+
+	spin_lock(&avic_vm_id_lock);
+
+	/* AVIC VM ID is one-based. */
+	id = find_next_zero_bit(avic_vm_id_bitmap, AVIC_VM_ID_NR, 1);
+	if (id <= AVIC_VM_ID_MASK)
+		__set_bit(id, avic_vm_id_bitmap);
+	else
+		id = -EAGAIN;
+
+	spin_unlock(&avic_vm_id_lock);
+	return id;
+}
+
+static inline int avic_free_vm_id(int id)
+{
+	if (id <= 0 || id > AVIC_VM_ID_MASK)
+		return -EINVAL;
+
+	spin_lock(&avic_vm_id_lock);
+	__clear_bit(id, avic_vm_id_bitmap);
+	spin_unlock(&avic_vm_id_lock);
+	return 0;
+}
+
 static void avic_vm_destroy(struct kvm *kvm)
 {
 	struct kvm_arch *vm_data = &kvm->arch;
 
+	avic_free_vm_id(vm_data->avic_vm_id);
+
 	if (vm_data->avic_logical_id_table_page)
 		__free_page(vm_data->avic_logical_id_table_page);
 	if (vm_data->avic_physical_id_table_page)
@@ -1300,6 +1347,10 @@ static int avic_vm_init(struct kvm *kvm)
 	if (!avic)
 		return 0;
 
+	vm_data->avic_vm_id = avic_get_next_vm_id();
+	if (vm_data->avic_vm_id < 0)
+		return vm_data->avic_vm_id;
+
 	/* Allocating physical APIC ID table (4KB) */
 	p_page = alloc_page(GFP_KERNEL);
 	if (!p_page)