linux-kernel - Re: [KVM PATCH v6 2/2] KVM: add iosignalfd support

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Date:	Mon, 15 Jun 2009 00:25:37 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, avi@...hat.com,
	davidel@...ilserver.org, paulmck@...ux.vnet.ibm.com,
	markmc@...hat.com, "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [KVM PATCH v6 2/2] KVM: add iosignalfd support

Hi Marcelo,

Marcelo Tosatti wrote:
> On Fri, Jun 05, 2009 at 12:02:02PM -0400, Gregory Haskins wrote:
>   
>> Hi Marcelo!
>>
>> Comments about the shutdown path ambiguity are in-line
>>
>> Gregory Haskins wrote:
>>     
>>> iosignalfd is a mechanism to register PIO/MMIO regions to trigger an eventfd
>>> signal when written to by a guest.  Host userspace can register any arbitrary
>>> IO address with a corresponding eventfd and then pass the eventfd to a
>>> +		list_del(&item->list);
>>> +		iosignalfd_item_free(item);
>>> +	}
>>> +
>>> +	list_del(&group->list);
>>> +	kfree(group);
>>> +}
>>>   
>>>       
>> So this function is called by the path that executes as we do the last
>> kvm_put_kvm().  I do not do any careful RCU wrangling here because I
>> assume that there cannot possibly be any active MMIO/PIO operations at
>> this time, or the reference would never have dropped.  Let me know if
>> anyone sees any holes in that.
>>
>> An alternative approach is to do this similar to how irqfd_release()
>> works.   That is: invoke it from the vmfd release() path instead of the
>> the kvm object destructor.  I currently do not think this is necessary,
>> but I will throw that out there in case someone likes it better.
>>     
>
> Gregory,
>
> Can't see any problems with it.

Thanks for the review!


>  You might want an upper limit
> in the number of items per group.
>   


Yeah, I agree that is a good idea.  Will fix in v7.

BTW: Did your series get merged while I was away?

-Greg


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