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>

9 files changed, 55 insertions, 33 deletions

diff --git a/arch/ia64/include/asm/kvm_host.h b/arch/ia64/include/asm/kvm_host.h
index 5f43697aed30..9cf1c4b1f92f 100644
--- a/arch/ia64/include/asm/kvm_host.h
+++ b/arch/ia64/include/asm/kvm_host.h
@@ -465,7 +465,6 @@ struct kvm_arch {
         unsigned long   metaphysical_rr4;
         unsigned long   vmm_init_rr;
 
-        int             online_vcpus;
         int             is_sn2;
 
         struct kvm_ioapic *vioapic;
diff --git a/arch/ia64/kvm/Kconfig b/arch/ia64/kvm/Kconfig
index f922bbba3797..cbadd8a65233 100644
--- a/arch/ia64/kvm/Kconfig
+++ b/arch/ia64/kvm/Kconfig
@@ -25,6 +25,7 @@ config KVM
         select PREEMPT_NOTIFIERS
         select ANON_INODES
         select HAVE_KVM_IRQCHIP
+        select KVM_APIC_ARCHITECTURE
         ---help---
           Support hosting fully virtualized guest machines using hardware
           virtualization extensions.  You will need a fairly recent
diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index 4082665ace0a..d1f7bcda2c7f 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -338,7 +338,7 @@ static struct kvm_vcpu *lid_to_vcpu(struct kvm *kvm, unsigned long id,
         union ia64_lid lid;
         int i;
 
-        for (i = 0; i < kvm->arch.online_vcpus; i++) {
+        for (i = 0; i < atomic_read(&kvm->online_vcpus); i++) {
                 if (kvm->vcpus[i]) {
                         lid.val = VCPU_LID(kvm->vcpus[i]);
                         if (lid.id == id && lid.eid == eid)
@@ -412,7 +412,7 @@ static int handle_global_purge(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 
         call_data.ptc_g_data = p->u.ptc_g_data;
 
-        for (i = 0; i < kvm->arch.online_vcpus; i++) {
+        for (i = 0; i < atomic_read(&kvm->online_vcpus); i++) {
                 if (!kvm->vcpus[i] || kvm->vcpus[i]->arch.mp_state ==
                                                 KVM_MP_STATE_UNINITIALIZED ||
                                         vcpu == kvm->vcpus[i])
@@ -852,8 +852,6 @@ struct  kvm *kvm_arch_create_vm(void)
 
         kvm_init_vm(kvm);
 
-        kvm->arch.online_vcpus = 0;
-
         return kvm;
 
 }
@@ -1356,8 +1354,6 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
                 goto fail;
         }
 
-        kvm->arch.online_vcpus++;
-
         return vcpu;
 fail:
         return ERR_PTR(r);
diff --git a/arch/ia64/kvm/vcpu.c b/arch/ia64/kvm/vcpu.c
index 61a3320b62c1..dce75b70cdd5 100644
--- a/arch/ia64/kvm/vcpu.c
+++ b/arch/ia64/kvm/vcpu.c
@@ -831,7 +831,7 @@ static void vcpu_set_itc(struct kvm_vcpu *vcpu, u64 val)
         kvm = (struct kvm *)KVM_VM_BASE;
 
         if (kvm_vcpu_is_bsp(vcpu)) {
-                for (i = 0; i < kvm->arch.online_vcpus; i++) {
+                for (i = 0; i < atomic_read(&kvm->online_vcpus); i++) {
                         v = (struct kvm_vcpu *)((char *)vcpu +
                                         sizeof(struct kvm_vcpu_data) * i);
                         VMX(v, itc_offset) = itc_offset;
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 8cd2a4efe238..7fbedfd34d6c 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -27,6 +27,7 @@ config KVM
         select ANON_INODES
         select HAVE_KVM_IRQCHIP
         select HAVE_KVM_EVENTFD
+        select KVM_APIC_ARCHITECTURE
         ---help---
           Support hosting fully virtualized guest machines using hardware
           virtualization extensions.  You will need a fairly recent
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index f1dada0519eb..5037e170a70d 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -430,6 +430,7 @@ struct kvm_trace_rec {
 #ifdef __KVM_HAVE_PIT
 #define KVM_CAP_PIT2 33
 #endif
+#define KVM_CAP_SET_BOOT_CPU_ID 34
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -537,6 +538,7 @@ struct kvm_irqfd {
 #define KVM_DEASSIGN_DEV_IRQ       _IOW(KVMIO, 0x75, struct kvm_assigned_irq)
 #define KVM_IRQFD                  _IOW(KVMIO, 0x76, struct kvm_irqfd)
 #define KVM_CREATE_PIT2            _IOW(KVMIO, 0x77, struct kvm_pit_config)
+#define KVM_SET_BOOT_CPU_ID        _IO(KVMIO, 0x78)
 
 /*
  * ioctls for vcpu fds
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a5bd429e9bd3..d3fdf1a738c9 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -131,8 +131,12 @@ struct kvm {
         int nmemslots;
         struct kvm_memory_slot memslots[KVM_MEMORY_SLOTS +
                                         KVM_PRIVATE_MEM_SLOTS];
+#ifdef CONFIG_KVM_APIC_ARCHITECTURE
+        u32 bsp_vcpu_id;
         struct kvm_vcpu *bsp_vcpu;
+#endif
         struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
+        atomic_t online_vcpus;
         struct list_head vm_list;
         struct mutex lock;
         struct kvm_io_bus mmio_bus;
@@ -550,8 +554,10 @@ static inline void kvm_irqfd_release(struct kvm *kvm) {}
 
 #endif /* CONFIG_HAVE_KVM_EVENTFD */
 
+#ifdef CONFIG_KVM_APIC_ARCHITECTURE
 static inline bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu)
 {
         return vcpu->kvm->bsp_vcpu == vcpu;
 }
 #endif
+#endif
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: