Re: [PATCH] xenpaging:close domU's event channel and free port

[Hongkaixing <hongkaixing@huawei.com>]

> -----Original Message-----
> From: Olaf Hering [mailto:olaf@aepfle.de]
> Sent: Saturday, February 11, 2012 12:40 AM
> To: hongkaixing@huawei.com
> Cc: xen-devel@lists.xensource.com; yanqiangjun@huawei.com; bicky.shi@huawei.com; xiaowei.yang@huawei.com;
> hanweidong@huawei.com
> Subject: Re: [PATCH] xenpaging:close domU's event channel and free port
> 
> On Thu, Feb 09, hongkaixing@huawei.com wrote:
> 
> > xenpaging:close domU's event channel and free port
> >
> > Every domain (X86 64 bit)has 4096 event channels.In source code,
> > domU's event channel is allocated in mem_event_enable(),but just
> > unbind dom0's event channel in xenpaging_teardown().This bug will
> > result in that we can not use xenpaging after reopening it for 4096
> > times.We should free domU's event channel in mem_event_disable().so
> > that we can reuse the port.
> 
> Does that fix a real bug?
> 
> xenpaging_teardown() does both xc_mem_paging_disable() and
> xc_evtchn_unbind(). The former fails often because the domain is gone
> and so it doesnt even reach the function in mem_event.c.
> The latter is called unconditionally.

   I have tested whether the kernel driver does a cleanup of all used ports once xenpaging exits.
Every domain has 1024 event channels.In xc_evtchn_unbind(),it just frees dom0's event channel's port,
and changes its state to be ECS_FREE;but the remote domain(domU)'s port is still ECS_UNBOUND.
so when each domU triggers 1024 times of xenpaging,it will fail of "Error initialising shared page
(28 = No space left on device): Internal error".Because there is no available free port for this domU.
Only the port's state is ECS_FREE,then it can be allocated by get_free_port();


> 
> Also I would expect that once xenpaging exits the kernel driver does a
> cleanup of all used ports. I havent checked wether thats true.
> 
> Olaf