Re: Is there any plan to support CXL GPF in Linux

[Dan Williams <dan.j.williams@intel.com>]

Yee Li wrote:
> Dear All,
> 
> Based on CXL Memory Device SW Guide and CXL Spec, the OS driver plays
> a part in the CXL GPF sequence for persistent memory (like Samsung
> CMM-H).
> 
> So, is there any plan to support CXL GPF in Linux?

See the "Maturity Map" [1] document for what the driver supports.

[1]: http://lore.kernel.org/172005486862.2048248.6668794717827294862.stgit@dwillia2-xfh.jf.intel.com

In terms of "plans", it is in the "patches welcome" state. While CXL
PMEM was an early focus of the kernel enabling, no PMEM devices
materialized in the market so focus moved elsewhere.

> Including init GPF DVSEC, flush data to GPF domain, etc.

One thing that guide does not cover is what should OS software do with a
dirty shutdown failure. To my knowledge there is no specific plumbing
for handling NVME device write-cache failures beyond: "hope filesystem
logging and metadata checksums can recover a consistent filesystem".

I do agree that the driver has a responsibility to set switch timeout
values, but that is more an unfortunate complexity imposed by the spec.
Just set the max and rely on devices to minimize GPF response times to
avoid the worst case wait times that those timeouts imply. In any event,
enabling that is "up for grabs."