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.