Re: [Ksummit-discuss] [CORE TOPIC] Device error handling / reporting / isolation

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Fri, 2014-05-09 at 13:19 -0700, James Bottomley wrote:
> > Defending against buggy hardware is interesting from a RAS perspective.
> > You don't want a card with a stuck address line scribbling on memory
> > that you didn't want it to touch.
> 
> But for a laptop or desktop kernel, how far do we want to go?  In
> theory, once the iommu is turned on, it corrals the device, since access
> to non programmed addresses (those without IOTLB entries) produces a
> fault.  Is there anything extra we need to do beyond turning on the
> IOMMU?

These tend to be the ones with the cheapest/buggiest hardware and less
prone to be affected by a 100ns overhead on PCIe transactions.

So they are the prime candidate for defaulting to a stricter protection
model.

They are also the ones likely to have an evil express card or whatever
that new PCIe-on-the-wire pushed by Apple & Intel or similar plugged into
them that tries to steal their data.

On the contrary, servers in controlled data centers using high end adapters
might wish to disable the IOMMU for performance reasons.

Cheers,
Ben.