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

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Message-ID: <20100602094527.GD964@8bytes.org>
Date:	Wed, 2 Jun 2010 11:45:27 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Avi Kivity <avi@...hat.com>
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 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.

	Joerg

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