[RFC PATCH 0/4] cxl/extent: Enable and validate multi-extent DCDs

[John Groves]

From: John Groves <john@xxxxxxxxxx>

This series fixes correctness issues in the DCD (Dynamic Capacity
Device) add-capacity pipeline so that multi-tag allocations, sharable
CDAT regions, and cross-partition checks work end-to-end.

Base
----

The series applies on top of Anisa Su's DCD stack — specifically the
tip of famfs-v9-dcd on the 'anisa' remote
(git@xxxxxxxxxx:anisa-su993/anisa-linux-kernel.git).  That stack is
the one posted to linux-cxl here:

  https://lore.kernel.org/linux-cxl/adnWg-60uKmduTsh@gourry-fedora-PF4VCD3F/T/#t

I started out commenting on prior series, then started modifying it,
before settling on this initial approach of generalizing the
functionality through additional patches. I'm hoping the stake holders
will find this easy to follow - at least as easy to follow as something
this tedious and nuanced can be.

Also, as one of the authors of the DCD spec: Now I get why this was hard
to follow and implement. The implementation is pretty complicated.

Note that this RFC builds happily, but I have not tested it yet. This
exercise has been about fleshing out the full logic.

The patches
-----------

 1) cxl/extent: Promote cxlr_dax->region_extent to an xarray

    Infrastructure only.  Replaces the single-slot region_extent
    pointer on struct cxl_dax_region with an xarray keyed by an
    allocator-assigned u32.  No behavior change; prepares storage for
    multiple tagged allocations per DAX-region shim.

 2) cxl/extent: Fix DCD add-capacity: per-tag assembly, ordering, and
    integrity

    Rewrites the add-capacity pipeline around the tag as the unit of
    allocation (not the More-chain).  Drops the DPA-contiguity reject,
    assembles each tag group separately, stable-sorts by
    shared_extn_seq, and adds cross-More-chain uniqueness,
    sequence-integrity, and alignment gates.  Lifts the single-slot
    "already onlined" gate now that (1) is in place.

 3) cxl/extent: Support extents in sharable CDAT regions

    Drops the per-extent rejection of shared_extn_seq != 0 and
    replaces it with a partition-aware check driven by the DSMAS
    SHAREABLE bit already exposed through cxl_dpa_partition.

 4) cxl/extent: Reject tagged extents that span DC partitions

    Adds a group-level check rejecting tagged allocations whose
    extents resolve to different DC partitions.  A single host-visible
    allocation cannot meaningfully straddle partitions whose CDAT
    attributes disagree.

Signed-off-by: John Groves <John@xxxxxxxxxx>

John Groves (4):
  cxl/extent: Promote cxlr_dax->region_extent to an xarray
  cxl/extent: Fix DCD add-capacity: per-tag assembly, ordering, and
    integrity
  cxl/extent: Support extents in sharable CDAT regions
  cxl/extent: Reject tagged extents that span DC partitions

 drivers/cxl/core/extent.c |  93 +++---
 drivers/cxl/core/mbox.c   | 628 +++++++++++++++++++++++++++++++-------
 drivers/cxl/core/region.c |   2 +
 drivers/cxl/cxl.h         |   9 +-
 include/cxl/event.h       |   1 -
 5 files changed, 584 insertions(+), 149 deletions(-)

-- 
2.53.0