From 6999ced63ca3bb05a1cbc4a667bd9fd27eeaeaee Mon Sep 17 00:00:00 2001
From: Salil Mehta <salil.mehta@huawei.com>
Date: Sat, 9 Sep 2023 00:04:04 +0000
Subject: [PATCH] accel/kvm: Extract common KVM vCPU {creation,parking} code

KVM vCPU creation is done once during the initialization of the VM when Qemu
threads are spawned. This is common to all the architectures. If the architecture
supports vCPU hot-{un}plug then this KVM vCPU creation could be deferred to
later point as well. Some architectures might in any case create KVM vCPUs for
the yet-to-be plugged vCPUs (i.e. QoM Object & thread does not exists) during VM
init time and park them.

Hot-unplug of vCPU results in destruction of the vCPU objects in QOM but
the KVM vCPU objects in the Host KVM are not destroyed and their representative
KVM vCPU objects in Qemu are parked.

Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
---
 accel/kvm/kvm-all.c  | 61 ++++++++++++++++++++++++++++++++++----------
 include/sysemu/kvm.h |  2 ++
 2 files changed, 49 insertions(+), 14 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index d900df93a4..6d503aa614 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -136,6 +136,7 @@ static QemuMutex kml_slots_lock;
 #define kvm_slots_unlock()  qemu_mutex_unlock(&kml_slots_lock)
 
 static void kvm_slot_init_dirty_bitmap(KVMSlot *mem);
+static int kvm_get_vcpu(KVMState *s, unsigned long vcpu_id);
 
 static inline void kvm_resample_fd_remove(int gsi)
 {
@@ -324,11 +325,51 @@ err:
     return ret;
 }
 
+void kvm_park_vcpu(CPUState *cpu)
+{
+    unsigned long vcpu_id = cpu->cpu_index;
+    struct KVMParkedVcpu *vcpu;
+
+    vcpu = g_malloc0(sizeof(*vcpu));
+    vcpu->vcpu_id = vcpu_id;
+    vcpu->kvm_fd = cpu->kvm_fd;
+    QLIST_INSERT_HEAD(&kvm_state->kvm_parked_vcpus, vcpu, node);
+}
+
+int kvm_create_vcpu(CPUState *cpu)
+{
+    unsigned long vcpu_id = cpu->cpu_index;
+    KVMState *s = kvm_state;
+    int ret;
+
+    DPRINTF("kvm_create_vcpu\n");
+
+    /* check if the KVM vCPU already exist but is parked */
+    ret = kvm_get_vcpu(s, kvm_arch_vcpu_id(cpu));
+    if (ret > 0) {
+        goto found;
+    }
+
+    /* create a new KVM vcpu */
+    ret = kvm_vm_ioctl(s, KVM_CREATE_VCPU, (void *)vcpu_id);
+    if (ret < 0) {
+        return ret;
+    }
+
+found:
+    cpu->vcpu_dirty = true;
+    cpu->kvm_fd = ret;
+    cpu->kvm_state = s;
+    cpu->dirty_pages = 0;
+    cpu->throttle_us_per_full = 0;
+
+    return 0;
+}
+
 static int do_kvm_destroy_vcpu(CPUState *cpu)
 {
     KVMState *s = kvm_state;
     long mmap_size;
-    struct KVMParkedVcpu *vcpu = NULL;
     int ret = 0;
 
     DPRINTF("kvm_destroy_vcpu\n");
@@ -357,10 +398,7 @@ static int do_kvm_destroy_vcpu(CPUState *cpu)
         }
     }
 
-    vcpu = g_malloc0(sizeof(*vcpu));
-    vcpu->vcpu_id = kvm_arch_vcpu_id(cpu);
-    vcpu->kvm_fd = cpu->kvm_fd;
-    QLIST_INSERT_HEAD(&kvm_state->kvm_parked_vcpus, vcpu, node);
+    kvm_park_vcpu(cpu);
 err:
     return ret;
 }
@@ -388,7 +426,7 @@ static int kvm_get_vcpu(KVMState *s, unsigned long vcpu_id)
         }
     }
 
-    return kvm_vm_ioctl(s, KVM_CREATE_VCPU, (void *)vcpu_id);
+    return -1;
 }
 
 int kvm_init_vcpu(CPUState *cpu, Error **errp)
@@ -399,19 +437,14 @@ int kvm_init_vcpu(CPUState *cpu, Error **errp)
 
     trace_kvm_init_vcpu(cpu->cpu_index, kvm_arch_vcpu_id(cpu));
 
-    ret = kvm_get_vcpu(s, kvm_arch_vcpu_id(cpu));
+    ret = kvm_create_vcpu(cpu);
     if (ret < 0) {
-        error_setg_errno(errp, -ret, "kvm_init_vcpu: kvm_get_vcpu failed (%lu)",
+        error_setg_errno(errp, -ret,
+                         "kvm_init_vcpu: kvm_create_vcpu failed (%lu)",
                          kvm_arch_vcpu_id(cpu));
         goto err;
     }
 
-    cpu->kvm_fd = ret;
-    cpu->kvm_state = s;
-    cpu->vcpu_dirty = true;
-    cpu->dirty_pages = 0;
-    cpu->throttle_us_per_full = 0;
-
     mmap_size = kvm_ioctl(s, KVM_GET_VCPU_MMAP_SIZE, 0);
     if (mmap_size < 0) {
         ret = mmap_size;
diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
index b46d6203b4..e534411ddc 100644
--- a/include/sysemu/kvm.h
+++ b/include/sysemu/kvm.h
@@ -434,6 +434,8 @@ void kvm_set_sigmask_len(KVMState *s, unsigned int sigmask_len);
 
 int kvm_physical_memory_addr_from_host(KVMState *s, void *ram_addr,
                                        hwaddr *phys_addr);
+int kvm_create_vcpu(CPUState *cpu);
+void kvm_park_vcpu(CPUState *cpu);
 
 #endif /* NEED_CPU_H */
 
-- 
2.27.0