[PATCH v4 5/9] cxl/region, dax/hmem: Arbitrate Soft Reserved ownership with cxl_regions_fully_map()

Smita Koralahalli
2025-11-20T03:19:56Z

Introduce cxl_regions_fully_map() to check whether CXL regions form a
single contiguous, non-overlapping cover of a given Soft Reserved range.

Use this helper to decide whether Soft Reserved memory overlapping CXL
regions should be owned by CXL or registered by HMEM.

If the span is fully covered by CXL regions, treat the Soft Reserved
range as owned by CXL and have HMEM skip registration. Else, let HMEM
claim the range and register the corresponding devdax for it.

Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
---
drivers/cxl/core/region.c | 80 +++++++++++++++++++++++++++++++++++++++
drivers/cxl/cxl.h | 6 +++
drivers/dax/hmem/hmem.c | 14 ++++++-
3 files changed, 99 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index b06fee1978ba..94dbbd6b5513 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -3749,6 +3749,86 @@ static int cxl_region_debugfs_poison_clear(void *data, u64 offset)
DEFINE_DEBUGFS_ATTRIBUTE(cxl_poison_clear_fops, NULL,
cxl_region_debugfs_poison_clear, "%llx\n");

+static struct cxl_region *
+cxlr_overlapping_range(struct device *dev, resource_size_t s, resource_size_t e)
+{
+ struct cxl_region *cxlr;
+ struct resource *r;
+
+ if (!is_cxl_region(dev))
+ return NULL;
+
+ cxlr = to_cxl_region(dev);
+ r = cxlr->params.res;
+ if (!r)
+ return NULL;
+
+ if (r->start > e || r->end < s)
+ return NULL;
+
+ return cxlr;
+}
+
+struct cxl_range_ctx {
+ resource_size_t start;
+ resource_size_t end;
+ resource_size_t pos;
+ resource_size_t map_end;
+ bool found;
+};
+
+static int cxl_region_map_cb(struct device *dev, void *data)
+{
+ struct cxl_range_ctx *ctx = data;
+ struct cxl_region *cxlr;
+ struct resource *r;
+
+ cxlr = cxlr_overlapping_range(dev, ctx->pos, ctx->end);
+ if (!cxlr)
+ return 0;
+
+ r = cxlr->params.res;
+ if (r->start != ctx->pos)
+ return 0;
+
+ if (!ctx->found) {
+ ctx->found = true;
+ ctx->map_end = r->end;
+ return 0;
+ }
+
+ return 1;
+}
+
+bool cxl_regions_fully_map(resource_size_t start, resource_size_t end)
+{
+ resource_size_t pos = start;
+ int rc;
+
+ while (pos <= end) {
+ struct cxl_range_ctx ctx = {
+ .start = start,
+ .end = end,
+ .pos = pos,
+ .found = false,
+ };
+
+ rc = bus_for_each_dev(&cxl_bus_type, NULL, &ctx,
+ cxl_region_map_cb);
+
+ if (rc || !ctx.found || ctx.map_end > end)
+ return false;
+
+ if (ctx.map_end == end)
+ break;
+
+ pos = ctx.map_end + 1;
+ }
+
+ return true;
+}
+EXPORT_SYMBOL_GPL(cxl_regions_fully_map);
+
static int cxl_region_can_probe(struct cxl_region *cxlr)
{
struct cxl_region_params *p = &cxlr->params;
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 231ddccf8977..af78c9fd37f2 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -877,6 +877,7 @@ struct cxl_pmem_region *to_cxl_pmem_region(struct device *dev);
int cxl_add_to_region(struct cxl_endpoint_decoder *cxled);
struct cxl_dax_region *to_cxl_dax_region(struct device *dev);
u64 cxl_port_get_spa_cache_alias(struct cxl_port *endpoint, u64 spa);
+bool cxl_regions_fully_map(resource_size_t start, resource_size_t end);
#else
static inline bool is_cxl_pmem_region(struct device *dev)
{
@@ -899,6 +900,11 @@ static inline u64 cxl_port_get_spa_cache_alias(struct cxl_port *endpoint,
{
return 0;
}
+static inline bool cxl_regions_fully_map(resource_size_t start,
+ resource_size_t end)
+{
+ return false;
+}
#endif

void cxl_endpoint_parse_cdat(struct cxl_port *port);
diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c
index f70a0688bd11..db4c46337ac3 100644
--- a/drivers/dax/hmem/hmem.c
+++ b/drivers/dax/hmem/hmem.c
@@ -3,6 +3,8 @@
#include <linux/memregion.h>
#include <linux/module.h>
#include <linux/dax.h>
+
+#include "../../cxl/cxl.h"
#include "../bus.h"

static bool region_idle;
@@ -150,7 +152,17 @@ static int hmem_register_device(struct device *host, int target_nid,
static int handle_deferred_cxl(struct device *host, int target_nid,
const struct resource *res)
{
- /* TODO: Handle region assembly failures */
+ if (region_intersects(res->start, resource_size(res), IORESOURCE_MEM,
+ IORES_DESC_CXL) != REGION_DISJOINT) {
+
+ if (cxl_regions_fully_map(res->start, res->end))
+ dax_cxl_mode = DAX_CXL_MODE_DROP;
+ else
+ dax_cxl_mode = DAX_CXL_MODE_REGISTER;
+
+ hmem_register_device(host, target_nid, res);
+ }
+
return 0;
}

--
2.17.1