On Thu, 2018-03-01 at 13:53 -0700, Jason Gunthorpe wrote:

On Fri, Mar 02, 2018 at 07:40:15AM +1100, Benjamin Herrenschmidt wrote:

quoted

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..

Could be that x86 has the smarts to do the right thing, still trying to
untangle the code :-)

Cheers,
Ben.