From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@scylladb.com>
Subject: Re: Having troubles binding an SR-IOV VF to
 uio_pci_generic on Amazon instance
Date: Thu, 1 Oct 2015 12:53:14 +0300
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On 10/01/2015 12:42 PM, Michael S. Tsirkin wrote:
> On Thu, Oct 01, 2015 at 12:22:46PM +0300, Avi Kivity wrote:
>> even when they are some users
>> prefer to avoid the performance penalty.
> I don't think there's a measureable penalty from passing through the
> IOMMU, as long as mappings are mostly static (i.e. iommu=pt).  I sure
> never saw any numbers that show such.
>

Maybe not.  But again, virtualized setups will not have a guest iommu 
and therefore can't use it; and those happen to be exactly the setups 
you're blocking.

Non-virtualized setups have an iommu available, but they can also use 
pci_uio_generic without patching if they like.

The virtualized setups have no other option; you're leaving them out in 
the cold.