Re: [PATCH RFC 01/17] mm: shmem: Implement guest_memfd provider operations for tmpfs

[Jason Gunthorpe]

On Thu, Oct 01, 2026 at 04:47:54PM +0100, David Woodhouse wrote:
> On Thu, 2026-10-01 at 11:17 -0300, Jason Gunthorpe wrote:

> > It would be nice if it could handle MMIO and "cachable MMIO" as well.
> 
> As opposed to just MMIO vs. RAM as implemented in the prototype in
> https://git.infradead.org/?p=users/dwmw2/linux.git;a=commitdiff;h=a7ca2d8859036 ?

Sort of, RAM is a little more permanent than "cachable mmio", I prefer
the latter because it conveys it is located on a device, is subject to
things like reset. Eg "CXL ram" would be cachable mmio.

I haven't heard of anything needing a unique PTE for this yet, but who
knows down the road.

> I think Fred has a cleaner version of that about ready to post as the
> next version of my series.

Yeah, cleaned up is needed, I want us to resolve this in the dmabuf
code cleanly not add more of the hack mess I made for vfio/iommufd..

Jason