linux-kernel - Re: [KVM PATCH v7 2/2] KVM: add iosignalfd support

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Message-ID: <4A3E3BC7.8040707@redhat.com>
Date:	Sun, 21 Jun 2009 16:55:19 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Gregory Haskins <ghaskins@...ell.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	davidel@...ilserver.org, mtosatti@...hat.com,
	paulmck@...ux.vnet.ibm.com, markmc@...hat.com
Subject: Re: [KVM PATCH v7 2/2] KVM: add iosignalfd support

On 06/18/2009 05:09 PM, Gregory Haskins wrote:
> Avi Kivity wrote:
>    
>> On 06/18/2009 03:09 PM, Gregory Haskins wrote:
>>      
>>>>> +config KVM_MAX_IOSIGNALFD_ITEMS
>>>>> +    int "Maximum IOSIGNALFD items per address"
>>>>> +    depends on KVM
>>>>> +    default "32"
>>>>> +    ---help---
>>>>> +      This option influences the maximum number of fd's per PIO/MMIO
>>>>> +      address that are allowed to register
>>>>> +
>>>>>
>>>>>
>>>>>            
>>>> Is there a per-vm limit on iosignalfds?  if not, userspace can exhaust
>>>> kernel memory in that way.
>>>>
>>>>          
>>> Yeah, its already naturally limited by the maximum number of MMIO/PIO
>>> devices we can register (today this is 6 per VM).  I should have
>>> documented that fact somewhere, tho.
>>>
>>>        
>> We need to raise this limit drastically and to expose it.
>>      
>
> Any suggestions on a target #?  512?
>    

Let's say 20 devices with 16 queues each.  That gives 320 fds.  So 512 
seems like a good choice for now.

But don't make it Kconfigurable, there's no way the user will know what 
to put there.
>> No, a u16 will naturally expand to a u64, and the emulator will
>> generate the correct value.
>>      
>
> Right, I understand that part.  What I mean specifically is at run-time
> when the IO comes in.  I was thinking I would need to do a memcmp
> against the u64 and the data-register and it was hurting my head trying
> to figure out what pointer to pass to memcmp.
>
> <lightbulb turns on>
>
> Duh, I can just load the data-register into a u64 and check equality.
> Nevermind, I am a dumbass ;)
>    

I see on your v8 what the load means.  It's not so pretty.  But we can 
have generic code do the load and pass a u64 instead of a pointer.

But please, only after this goes in.

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

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