linux-kernel - Re: [KVM PATCH v8 3/3] KVM: add iosignalfd support

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Message-ID: <4A40BB73.600@redhat.com>
Date:	Tue, 23 Jun 2009 14:24:35 +0300
From:	Avi Kivity <avi@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Gregory Haskins <ghaskins@...ell.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, mtosatti@...hat.com,
	paulmck@...ux.vnet.ibm.com, markmc@...hat.com
Subject: Re: [KVM PATCH v8 3/3] KVM: add iosignalfd support

On 06/23/2009 01:48 PM, Michael S. Tsirkin wrote:
> On Tue, Jun 23, 2009 at 12:57:53PM +0300, Avi Kivity wrote:
>    
>> On 06/23/2009 11:56 AM, Michael S. Tsirkin wrote:
>>      
>>> On Thu, Jun 18, 2009 at 08:30:46PM -0400, Gregory Haskins wrote:
>>>
>>>        
>>>> +static int
>>>> +iosignalfd_group_in_range(struct kvm_io_device *this, gpa_t addr, int len,
>>>> +			  int is_write)
>>>> +{
>>>> +	struct _iosignalfd_group *p = to_group(this);
>>>> +
>>>> +	return ((addr>= p->addr&&   (addr<   p->addr + p->length)));
>>>> +}
>>>>
>>>>          
>>> I think I see a problem here. For virtio, we do not necessarily want all
>>> virtqueues for a device to live in kernel: there might be control
>>> virtqueues that we want to leave in userspace. Since this claims all
>>> writes to a specific address, the signal never makes it to userspace.
>>>
>>>        
>> Userspace could create an eventfd for this control queue and wait for it
>> to fire.
>>      
>
> What if guest writes an unexpected value there?
> The value it simply lost ... that's not very elegant.
>    

True, it's better to have a lossless interface.

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

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