Re: [PATCH] KVM: x86: should release vcpu when closing vcpu fd

[Gleb Natapov <gleb@redhat.com>]

On Thu, Aug 29, 2013 at 11:06:47AM +0800, chenfan wrote:
> On Wed, 2013-08-28 at 11:21 +0300, Gleb Natapov wrote:
> > On Wed, Aug 28, 2013 at 04:08:10PM +0800, Chen Fan wrote:
> > > If we want to remove a vcpu from vm, we should not be only to
> > > put kvm, we need to decrease online vcpus and free struct kvm_vcpu
> > > when closing a vcpu file descriptor.
> > > 
> > It much more complicated that what you do here. kvm->vcpus[] is accessed
> > without locking and kvm->online_vcpus is assumed to be greater than max
> > occupied index in kvm->vcpus[]. Attempt where made to make it possible
> > to destroy individual vcpus separately from destroying VM before, but
> > they were unsuccessful thus far.
> > 
> Oh, the motivation of this patch is for QEMU for implementing cpu
> hot-remove, I want to remove the vcpu from KVM after QEMU closing the
> kvm_fd. there I need some advice for this feature. if this patch is not
> comprehensive enough，I want to know the reasons for a more detailed.
> Could you tell me?
> 
I told you above.

> Thanks,
> Chen
> 
> > > Signed-off-by: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> > > ---
> > >  arch/x86/kvm/x86.c       | 14 ++++++++++++++
> > >  include/linux/kvm_host.h |  1 +
> > >  virt/kvm/kvm_main.c      |  4 +++-
> > >  3 files changed, 18 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > index d21bce5..3370de1 100644
> > > --- a/arch/x86/kvm/x86.c
> > > +++ b/arch/x86/kvm/x86.c
> > > @@ -6904,6 +6904,20 @@ static void kvm_free_vcpus(struct kvm *kvm)
> > >  	mutex_unlock(&kvm->lock);
> > >  }
> > >  
> > > +void kvm_arch_vcpu_release(struct kvm_vcpu *vcpu)
> > > +{
> > > +	struct kvm *kvm = vcpu->kvm;
> > > +
> > > +	mutex_lock(&kvm->lock);
> > > +	atomic_dec(&kvm->online_vcpus);
> > > +	kvm->vcpus[atomic_read(&kvm->online_vcpus)] = NULL;
> > > +	mutex_unlock(&kvm->lock);
> > > +
> > > +	kvm_clear_async_pf_completion_queue(vcpu);
> > > +	kvm_unload_vcpu_mmu(vcpu);
> > > +	kvm_arch_vcpu_free(vcpu);
> > > +}
> > > +
> > >  void kvm_arch_sync_events(struct kvm *kvm)
> > >  {
> > >  	kvm_free_all_assigned_devices(kvm);
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index a63d83e..e0811f97 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -631,6 +631,7 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id);
> > >  int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu);
> > >  int kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu);
> > >  void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu);
> > > +void kvm_arch_vcpu_release(struct kvm_vcpu *vcpu);
> > >  
> > >  int kvm_arch_hardware_enable(void *garbage);
> > >  void kvm_arch_hardware_disable(void *garbage);
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index 1580dd4..442014b 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -1873,8 +1873,10 @@ 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);
> > > +	kvm_arch_vcpu_release(vcpu);
> > > +	kvm_put_kvm(kvm);
> > >  	return 0;
> > >  }
> > >  
> > > -- 
> > > 1.8.1.4
> > > 
> > > --
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> > 
> > --
> > 			Gleb.
> > --
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> 

--
			Gleb.