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

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Message-ID: <20090623104812.GB17635@redhat.com>
Date:	Tue, 23 Jun 2009 13:48:12 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Avi Kivity <avi@...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 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.

-- 
MST
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