Re: [Qemu-devel] [PATCH 1/2] kvm: make vcpu life cycle separated from kvm instance

[Avi Kivity]

On 11/25/2011 04:35 AM, Liu Ping Fan wrote:
> From: Liu Ping Fan <address@hidden>
>
> Currently, vcpu can be destructed only when kvm instance destroyed.
> Change this to vcpu as a refer to kvm, and then vcpu MUST and CAN be
> destroyed before kvm's destroy. Qemu will take advantage of this to
> exit the vcpu thread if the thread is no longer in use by guest.
>
> Signed-off-by: Liu Ping Fan <address@hidden>
> ---
>  arch/x86/kvm/x86.c       |   28 ++++++++--------------------
>  include/linux/kvm_host.h |    2 ++
>  virt/kvm/kvm_main.c      |   31 +++++++++++++++++++++++++++++--
>  3 files changed, 39 insertions(+), 22 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c38efd7..ea2315a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6560,27 +6560,16 @@ static void kvm_unload_vcpu_mmu(struct kvm_vcpu *vcpu)
>       vcpu_put(vcpu);
>  }
>  
> -static void kvm_free_vcpus(struct kvm *kvm)
> +void kvm_arch_vcpu_zap(struct kref *ref)
>  {
> -     unsigned int i;
> -     struct kvm_vcpu *vcpu;
> -
> -     /*
> -      * Unpin any mmu pages first.
> -      */
> -     kvm_for_each_vcpu(i, vcpu, kvm) {
> -             kvm_clear_async_pf_completion_queue(vcpu);
> -             kvm_unload_vcpu_mmu(vcpu);
> -     }
> -     kvm_for_each_vcpu(i, vcpu, kvm)
> -             kvm_arch_vcpu_free(vcpu);
> -
> -     mutex_lock(&kvm->lock);
> -     for (i = 0; i < atomic_read(&kvm->online_vcpus); i++)
> -             kvm->vcpus[i] = NULL;
> +     struct kvm_vcpu *vcpu = container_of(ref, struct kvm_vcpu, refcount);
> +     struct kvm *kvm = vcpu->kvm;
>  
> -     atomic_set(&kvm->online_vcpus, 0);
> -     mutex_unlock(&kvm->lock);
> +     printk(KERN_INFO "%s, zap vcpu:0x%x\n", __func__, vcpu->vcpu_id);
> +     kvm_clear_async_pf_completion_queue(vcpu);
> +     kvm_unload_vcpu_mmu(vcpu);
> +     kvm_arch_vcpu_free(vcpu);
> +     kvm_put_kvm(kvm);
>  }
>  
>  void kvm_arch_sync_events(struct kvm *kvm)
> @@ -6594,7 +6583,6 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
>       kvm_iommu_unmap_guest(kvm);
>       kfree(kvm->arch.vpic);
>       kfree(kvm->arch.vioapic);
> -     kvm_free_vcpus(kvm);
>       if (kvm->arch.apic_access_page)
>               put_page(kvm->arch.apic_access_page);
>       if (kvm->arch.ept_identity_pagetable)
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index d526231..fe35078 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -113,6 +113,7 @@ enum {
>  
>  struct kvm_vcpu {
>       struct kvm *kvm;
> +     struct kref refcount;
>  #ifdef CONFIG_PREEMPT_NOTIFIERS
>       struct preempt_notifier preempt_notifier;
>  #endif
> @@ -460,6 +461,7 @@ void kvm_arch_exit(void);
>  int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu);
>  void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu);
>  
> +void kvm_arch_vcpu_zap(struct kref *ref);
>  void kvm_arch_vcpu_free(struct kvm_vcpu *vcpu);
>  void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
>  void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index d9cfb78..f166bc8 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -580,6 +580,7 @@ static void kvm_destroy_vm(struct kvm *kvm)
>       kvm_arch_free_vm(kvm);
>       hardware_disable_all();
>       mmdrop(mm);
> +     printk(KERN_INFO "%s finished\n", __func__);
>  }
>  
>  void kvm_get_kvm(struct kvm *kvm)
> @@ -1503,6 +1504,16 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
>       mark_page_dirty_in_slot(kvm, memslot, gfn);
>  }
>  
> +void kvm_vcpu_get(struct kvm_vcpu *vcpu)
> +{
> +     kref_get(&vcpu->refcount);
> +}
> +
> +void kvm_vcpu_put(struct kvm_vcpu *vcpu)
> +{
> +     kref_put(&vcpu->refcount, kvm_arch_vcpu_zap);
> +}
> +
>  /*
>   * The vCPU has executed a HLT instruction with in-kernel mode enabled.
>   */
> @@ -1623,8 +1634,13 @@ static int kvm_vcpu_mmap(struct file *file, struct 
> vm_area_struct *vma)
>  static int kvm_vcpu_release(struct inode *inode, struct file *filp)
>  {
>       struct kvm_vcpu *vcpu = filp->private_data;
> +     struct kvm *kvm = vcpu->kvm;
>  
> -     kvm_put_kvm(vcpu->kvm);
> +     filp->private_data = NULL;
> +     mutex_lock(&kvm->lock);
> +     atomic_sub(1, &kvm->online_vcpus);
> +     mutex_unlock(&kvm->lock);
> +     kvm_vcpu_put(vcpu);
>       return 0;
>  }
>  
> @@ -1646,6 +1662,17 @@ static int create_vcpu_fd(struct kvm_vcpu *vcpu)
>       return anon_inode_getfd("kvm-vcpu", &kvm_vcpu_fops, vcpu, O_RDWR);
>  }
>  
> +static struct kvm_vcpu *kvm_vcpu_create(struct kvm *kvm, u32 id)
> +{
> +     struct kvm_vcpu *vcpu;
> +     vcpu = kvm_arch_vcpu_create(kvm, id);
> +     if (IS_ERR(vcpu))
> +             return vcpu;
> +
> +     kref_init(&vcpu->refcount);
> +     return vcpu;
> +}
> +
>  /*
>   * Creates some virtual cpus.  Good luck creating more than one.
>   */
> @@ -1654,7 +1681,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, 
> u32 id)
>       int r;
>       struct kvm_vcpu *vcpu, *v;
>  
> -     vcpu = kvm_arch_vcpu_create(kvm, id);
> +     vcpu = kvm_vcpu_create(kvm, id);
>       if (IS_ERR(vcpu))
>               return PTR_ERR(vcpu);
>  

I don't think this is sufficient to actually remove a vcpu from the vcpu
table.  It may be referred to from other vcpus in the local APIC code. 
Practically the only thing that can accomplish this without a
substantial effort is rcu.

-- 
error compiling committee.c: too many arguments to function