Re: [PATCH v10 16/31] cxl/extent: Validate DC extent partition

[Dave Jiang <dave.jiang@intel.com>]

On 5/23/26 2:43 AM, Anisa Su wrote:
> Extend cxl_validate_extent() — the per-extent check of the add pipeline
> to check partition membership.
> 
> Resolves an extent's DPA to its containing DC partition. Then based on
> if the partition is shareable:
> 
>   - Shareable: tag must be non-null and shared_extn_seq must be non-zero
>     — multiple hosts reading the same allocation rely on the device-
>     stamped 1..n sequence to assemble extents in agreed order.
>   - Non-sharable: shared_extn_seq must be zero — sequencing is
>     meaningless when only one host consumes the allocation; tag is
>     optional (null UUID permitted).
> 
> Any cross-mix is a device firmware bug; reject the extent.
> 
> Based on patches by John Groves.
> 
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: John Groves <John@Groves.net>
> Signed-off-by: Anisa Su <anisa.su@samsung.com>
> 
> ---
> Changes:
> [anisa: split out as a separate validation step]
> ---
>  drivers/cxl/core/core.h   |  4 ++
>  drivers/cxl/core/extent.c | 78 +++++++++++++++++++++++++++++++++++++--
>  2 files changed, 79 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/cxl/core/core.h b/drivers/cxl/core/core.h
> index 1bae80dbf991..30b6b05b155b 100644
> --- a/drivers/cxl/core/core.h
> +++ b/drivers/cxl/core/core.h
> @@ -179,6 +179,10 @@ int cxl_pci_get_bandwidth(struct pci_dev *pdev, struct access_coordinate *c);
>  int cxl_port_get_switch_dport_bandwidth(struct cxl_port *port,
>  					struct access_coordinate *c);
>  void memdev_release_extent(struct cxl_memdev_state *mds, struct range *range);
> +const struct cxl_dpa_partition *
> +cxl_extent_dc_partition(struct cxl_memdev_state *mds,
> +			struct cxl_extent *extent,
> +			struct range *ext_range);
>  
>  static inline struct device *port_to_host(struct cxl_port *port)
>  {
> diff --git a/drivers/cxl/core/extent.c b/drivers/cxl/core/extent.c
> index 94128d06f4ed..b01507022cff 100644
> --- a/drivers/cxl/core/extent.c
> +++ b/drivers/cxl/core/extent.c
> @@ -63,11 +63,55 @@ alloc_tag_group(struct cxl_dax_region *cxlr_dax, uuid_t *uuid)
>  	return no_free_ptr(group);
>  }
>  
> +/*
> + * Find the DC (Dynamic Capacity) partition that fully contains @ext_range,
> + * or NULL if the extent falls outside every DC partition on this memdev.
> + * The returned pointer is owned by mds->cxlds.part[] and lives for the
> + * lifetime of the memdev.
> + */
> +const struct cxl_dpa_partition *
> +cxl_extent_dc_partition(struct cxl_memdev_state *mds,
> +			struct cxl_extent *extent,
> +			struct range *ext_range)

This can be static, given it's only called in extent.c

> +{
> +	struct cxl_dev_state *cxlds = &mds->cxlds;
> +	struct device *dev = mds->cxlds.dev;
> +
> +	for (int i = 0; i < cxlds->nr_partitions; i++) {
> +		struct cxl_dpa_partition *part = &cxlds->part[i];
> +		struct range partition_range = {
> +			.start = part->res.start,
> +			.end = part->res.end,
> +		};
> +
> +		if (part->mode != CXL_PARTMODE_DYNAMIC_RAM_A)
> +			continue;
> +
> +		if (range_contains(&partition_range, ext_range)) {
> +			dev_dbg(dev, "DC extent DPA %pra (DCR:%pra)(%pU)\n",
> +				ext_range, &partition_range, extent->uuid);
> +			return part;
> +		}
> +	}
> +
> +	dev_err_ratelimited(dev,
> +			    "DC extent DPA %pra (%pU) is not in a valid DC partition\n",
> +			    ext_range, extent->uuid);
> +	return NULL;
> +}
> +
>  /*
>   * Stage 1 of the add pipeline: pure, no allocation.  Resolve the extent
> - * to its region/endpoint decoder and ext_range, and verify the range
> - * fits in the resolved endpoint decoder's DPA resource.  Further
> - * per-extent invariants layer into this function in subsequent commits.
> + * to its region/endpoint decoder and ext_range, and enforce every
> + * per-extent invariant the device must satisfy:
> + *
> + *   - DPA falls inside a Dynamic Capacity partition (cxl_extent_dc_partition).
> + *   - CDAT-sharability rules:
> + *       sharable:     tag must be non-null AND shared_extn_seq != 0
> + *       non-sharable: shared_extn_seq must be 0  (tag is optional)
> + *     Any cross-mixing is a device firmware bug.
> + *   - DPA resolves to an endpoint decoder attached to a region.
> + *   - The extent's range is fully contained in that ED's DPA resource.
>   *
>   * Caller must hold cxl_rwsem.region for read (cxl_dpa_to_region()).
>   * On success, @out_cxled / @out_cxlr_dax / @out_ext_range carry the
> @@ -81,6 +125,10 @@ static int cxl_validate_extent(struct cxl_memdev_state *mds,
>  {
>  	u64 start_dpa = le64_to_cpu(extent->start_dpa);
>  	struct cxl_memdev *cxlmd = mds->cxlds.cxlmd;
> +	struct device *dev = mds->cxlds.dev;
> +	uuid_t *uuid = (uuid_t *)extent->uuid;

Consider using import_uuid() instead of direct cast.

> +	u16 seq = le16_to_cpu(extent->shared_extn_seq);
> +	const struct cxl_dpa_partition *part;
>  	struct cxl_endpoint_decoder *cxled;
>  	struct cxl_region *cxlr;
>  	struct range ext_range = (struct range) {
> @@ -89,6 +137,30 @@ static int cxl_validate_extent(struct cxl_memdev_state *mds,
>  	};
>  	struct range ed_range;
>  
> +	part = cxl_extent_dc_partition(mds, extent, &ext_range);
> +	if (!part)
> +		return -ENXIO;
> +
> +	if (part->perf.shareable) {
> +		if (uuid_is_null(uuid)) {
> +			dev_err_ratelimited(dev,
> +				"DC extent DPA %pra: sharable-partition extent has null tag (firmware bug)\n",
> +				&ext_range);
> +			return -ENXIO;
> +		}
> +		if (seq == 0) {

I don't think this complies with the spec language. In r4.0 Table 8-230: "For extents describing shareable regions this field shall be within the range of 0 to n-1 where n is the number of extents, with each value appearing only once." So seq == 0 is an acceptable value.

Also, looking at cxl_add_pending() @ line ~1396, does shared seq number '0' holds special meanings? Maybe that needs to change? Also suggest adding comments to point out what's happening there if '0' is special. 

DJ


> +			dev_err_ratelimited(dev,
> +				"DC extent DPA %pra (%pU): sharable-partition extent missing shared_extn_seq (firmware bug)\n",
> +				&ext_range, uuid);
> +			return -ENXIO;
> +		}
> +	} else if (seq != 0) {
> +		dev_err_ratelimited(dev,
> +			"DC extent DPA %pra (%pU): non-sharable partition but shared_extn_seq=%u (firmware bug)\n",
> +			&ext_range, uuid, seq);
> +		return -ENXIO;
> +	}
> +
>  	cxlr = cxl_dpa_to_region(cxlmd, start_dpa, &cxled);
>  	if (!cxlr)
>  		return -ENXIO;