KVM: Break dependency between vcpu index in vcpus array and vcpu_id.

Archs are free to use vcpu_id as they see fit. For x86 it is used as
vcpu's apic id. New ioctl is added to configure boot vcpu id that was
assumed to be 0 till now.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

2 files changed, 42 insertions, 25 deletions

diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index 56c6848d2df8..daece36c0a57 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -9,3 +9,6 @@ config HAVE_KVM_IRQCHIP
 config HAVE_KVM_EVENTFD
        bool
        select EVENTFD
+
+config KVM_APIC_ARCHITECTURE
+       bool
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 0d54edecbc70..25e1f9c97b1a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -689,11 +689,6 @@ out:
 }
 #endif
 
-static inline int valid_vcpu(int n)
-{
-        return likely(n >= 0 && n < KVM_MAX_VCPUS);
-}
-
 inline int kvm_is_mmio_pfn(pfn_t pfn)
 {
         if (pfn_valid(pfn)) {
@@ -1714,24 +1709,18 @@ static struct file_operations kvm_vcpu_fops = {
  */
 static int create_vcpu_fd(struct kvm_vcpu *vcpu)
 {
-        int fd = anon_inode_getfd("kvm-vcpu", &kvm_vcpu_fops, vcpu, 0);
-        if (fd < 0)
-                kvm_put_kvm(vcpu->kvm);
-        return fd;
+        return anon_inode_getfd("kvm-vcpu", &kvm_vcpu_fops, vcpu, 0);
 }
 
 /*
  * Creates some virtual cpus.  Good luck creating more than one.
  */
-static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)
+static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
 {
         int r;
         struct kvm_vcpu *vcpu;
 
-        if (!valid_vcpu(n))
-                return -EINVAL;
-
-        vcpu = kvm_arch_vcpu_create(kvm, n);
+        vcpu = kvm_arch_vcpu_create(kvm, id);
         if (IS_ERR(vcpu))
                 return PTR_ERR(vcpu);
 
@@ -1742,25 +1731,38 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)
                 return r;
 
         mutex_lock(&kvm->lock);
-        if (kvm->vcpus[n]) {
-                r = -EEXIST;
+        if (atomic_read(&kvm->online_vcpus) == KVM_MAX_VCPUS) {
+                r = -EINVAL;
                 goto vcpu_destroy;
         }
-        kvm->vcpus[n] = vcpu;
-        if (n == 0)
-                kvm->bsp_vcpu = vcpu;
-        mutex_unlock(&kvm->lock);
+
+        for (r = 0; r < atomic_read(&kvm->online_vcpus); r++)
+                if (kvm->vcpus[r]->vcpu_id == id) {
+                        r = -EEXIST;
+                        goto vcpu_destroy;
+                }
+
+        BUG_ON(kvm->vcpus[atomic_read(&kvm->online_vcpus)]);
 
         /* Now it's all set up, let userspace reach it */
         kvm_get_kvm(kvm);
         r = create_vcpu_fd(vcpu);
-        if (r < 0)
-                goto unlink;
+        if (r < 0) {
+                kvm_put_kvm(kvm);
+                goto vcpu_destroy;
+        }
+
+        kvm->vcpus[atomic_read(&kvm->online_vcpus)] = vcpu;
+        smp_wmb();
+        atomic_inc(&kvm->online_vcpus);
+
+#ifdef CONFIG_KVM_APIC_ARCHITECTURE
+        if (kvm->bsp_vcpu_id == id)
+                kvm->bsp_vcpu = vcpu;
+#endif
+        mutex_unlock(&kvm->lock);
         return r;
 
-unlink:
-        mutex_lock(&kvm->lock);
-        kvm->vcpus[n] = NULL;
 vcpu_destroy:
         mutex_unlock(&kvm->lock);
         kvm_arch_vcpu_destroy(vcpu);
@@ -2233,6 +2235,15 @@ static long kvm_vm_ioctl(struct file *filp,
                 r = kvm_irqfd(kvm, data.fd, data.gsi, data.flags);
                 break;
         }
+#ifdef CONFIG_KVM_APIC_ARCHITECTURE
+        case KVM_SET_BOOT_CPU_ID:
+                r = 0;
+                if (atomic_read(&kvm->online_vcpus) != 0)
+                        r = -EBUSY;
+                else
+                        kvm->bsp_vcpu_id = arg;
+                break;
+#endif
         default:
                 r = kvm_arch_vm_ioctl(filp, ioctl, arg);
         }
@@ -2299,6 +2310,9 @@ static long kvm_dev_ioctl_check_extension_generic(long arg)
         case KVM_CAP_USER_MEMORY:
         case KVM_CAP_DESTROY_MEMORY_REGION_WORKS:
         case KVM_CAP_JOIN_MEMORY_REGIONS_WORKS:
+#ifdef CONFIG_KVM_APIC_ARCHITECTURE
+        case KVM_CAP_SET_BOOT_CPU_ID:
+#endif
                 return 1;
 #ifdef CONFIG_HAVE_KVM_IRQCHIP
         case KVM_CAP_IRQ_ROUTING: