From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: Having troubles binding an SR-IOV VF to
 uio_pci_generic on Amazon instance
Date: Wed, 30 Sep 2015 21:55:31 +0300
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On Wed, Sep 30, 2015 at 09:15:56PM +0300, Vlad Zolotarov wrote:
> 
> 
> On 09/30/15 18:26, Michael S. Tsirkin wrote:
> >On Wed, Sep 30, 2015 at 03:50:09PM +0300, Vlad Zolotarov wrote:
> >>How not virtualizing iommu forces "all or nothing" approach?
> >Looks like you can't limit an assigned device to only access part of
> >guest memory that belongs to a given process.  Either let it access all
> >of guest memory ("all") or don't assign the device ("nothing").
> 
> Ok. A question then: can u limit the assigned device to only access part of
> the guest memory even if iommu was virtualized?

That's exactly what an iommu does - limit the device io access to memory.

> How would iommu
> virtualization change anything?

Kernel can use an iommu to limit device access to memory of
the controlling application.

> And why do we care about an assigned device
> to be able to access all Guest memory?

Because we want to be reasonably sure a kernel memory corruption
is not a result of a bug in a userspace application.

-- 
MST