linux-kernel - Re: [PATCH] VFIO driver: Non-privileged user level PCI drivers

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Date:	Wed, 02 Jun 2010 12:49:28 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Joerg Roedel <joro@...tes.org>
CC:	"Michael S. Tsirkin" <mst@...hat.com>, Tom Lyon <pugs@...co.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	chrisw@...s-sol.org, hjk@...utronix.de, gregkh@...e.de,
	aafabbri@...co.com, scofeldm@...co.com
Subject: Re: [PATCH] VFIO driver: Non-privileged user level PCI drivers

On 06/02/2010 12:45 PM, Joerg Roedel wrote:
> On Tue, Jun 01, 2010 at 03:41:55PM +0300, Avi Kivity wrote:
>    
>> On 06/01/2010 01:46 PM, Michael S. Tsirkin wrote:
>>      
>    
>>> Main difference is that vhost works fine with unlocked
>>> memory, paging it in on demand. iommu needs to unmap
>>> memory when it is swapped out or relocated.
>>>
>>>        
>> So you'd just take the memory map and not pin anything.  This way you
>> can reuse the memory map.
>>
>> But no, it doesn't handle the dirty bitmap, so no go.
>>      
> IOMMU mapped memory can not be swapped out because we can't do demand
> paging on io-page-faults with current devices. We have to pin _all_
> userspace memory that is mapped into an IOMMU domain.
>    

vhost doesn't pin memory.

What I proposed is to describe the memory map using an object (fd), and 
pass it around to clients that use it: kvm, vhost, vfio.  That way you 
maintain the memory map in a central location and broadcast changes to 
clients.  Only a vfio client would result in memory being pinned.

It can still work, but the interface needs to be extended to include 
dirty bitmap logging.

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

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