Re: [Xen-devel] [PATCH 3/3] VMX: Remove the vcpu from the per-cpu blocking list after domain termination

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.05.16 at 07:48, <feng.wu@xxxxxxxxx> wrote:
>> From: Tian, Kevin
>> Sent: Monday, May 23, 2016 1:19 PM
>> > From: Wu, Feng
>> > Sent: Friday, May 20, 2016 4:54 PM
>> > --- a/xen/arch/x86/hvm/vmx/vmx.c
>> > +++ b/xen/arch/x86/hvm/vmx/vmx.c
>> > @@ -248,6 +248,36 @@ void vmx_pi_hooks_deassign(struct domain *d)
>> >      d->arch.hvm_domain.vmx.pi_switch_to = NULL;
>> >  }
>> >
>> > +static void vmx_pi_blocking_list_cleanup(struct domain *d)
>> 
>> Is it more natural to move such cleanup under vcpu destroy?
> 
> Yes, indeed it is more natural to add this function when vcpu is destroyed,
> however, the reason I add it here is I still have some concerns about the 
> timing.
> When the VM is destroyed, here is the calling path:
> 
> - vmx_pi_hooks_deassign() -->
> ......
> - vmx_vcpu_destroy() --> 
> ......
> - vmx_domain_destroy()
> ......
> 
> As I replied in the previous mail, when we remove the vcpus from the 
> blocking
> list, there might be some _in-flight_ call to the hooks, so I put the cleanup
> code in the vmx_domain_destroy(), which is a bit more far from 
> vmx_pi_hooks_deassign,
> and hence safer. If you have any other good ideas, I am all ears!:)

Well, either there is a possible race (then moving the addition
later just reduces the chances, but doesn't eliminate it), or there
isn't (in which case Kevin's suggestion should probably be followed).

Jan


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