[PATCH v2 00/10] Copy Offload in NVMe Fabrics with P2P PCI Memory

[Jason Gunthorpe]

On Fri, Mar 02, 2018 at 07:40:15AM +1100, Benjamin Herrenschmidt wrote:
> Also we need to be able to hard block MEMREMAP_WB mappings of non-RAM
> on ppc64 (maybe via an arch hook as it might depend on the processor
> family). Server powerpc cannot do cachable accesses on IO memory
> (unless it's special OpenCAPI or nVlink, but not on PCIe).

I think you are right on this - even on x86 we must not create
cachable mappings of PCI BARs - there is no way that works the way
anyone would expect.

I think this series doesn't have a problem here only because it never
touches the BAR pages with the CPU.

BAR memory should be mapped into the CPU as WC at best on all arches..

Jason