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From: "Michael S. Tsirkin" <mst@redhat.com>
To: Avi Kivity <avi@scylladb.com>
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Subject: Re: [dpdk-dev] Having troubles binding an SR-IOV VF to
 uio_pci_generic on Amazon instance
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On Thu, Oct 01, 2015 at 12:43:53PM +0300, Avi Kivity wrote:
> >There were some tentative to get it for other (older) drivers, named
> >'bifurcated drivers', but it is stalled.
> 
> IIRC they still exposed the ring to userspace.

How much would a ring write syscall cost? 1-2 microseconds, isn't it?
Measureable, but it's not the end of the world.
ring read might be safe to allow.
Should buy us enough time until hypervisors support IOMMU.

-- 
MST