[PATCH v4 8/9] cxl/region, dax/hmem: Tear down CXL regions when HMEM reclaims Soft Reserved

Smita Koralahalli
2025-11-20T03:20:00Z

If CXL regions do not fully cover a Soft Reserved span, HMEM takes
ownership. Tear down overlapping CXL regions before allowing HMEM to
register and online the memory.

Add cxl_region_teardown() to walk CXL regions overlapping a span and
unregister them via devm_release_action() and unregister_region().

Force the region state back to CXL_CONFIG_ACTIVE before unregistering to
prevent the teardown path from resetting decoders HMEM still relies on
to create its dax and online memory.

Co-developed-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
---
drivers/cxl/core/region.c | 38 ++++++++++++++++++++++++++++++++++++++
drivers/cxl/cxl.h | 5 +++++
drivers/dax/hmem/hmem.c | 4 +++-
3 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 38e7ec6a087b..266b24028df0 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -3784,6 +3784,44 @@ struct cxl_range_ctx {
bool found;
};

+static int cxl_region_teardown_cb(struct device *dev, void *data)
+{
+ struct cxl_range_ctx *ctx = data;
+ struct cxl_root_decoder *cxlrd;
+ struct cxl_region_params *p;
+ struct cxl_region *cxlr;
+ struct cxl_port *port;
+
+ cxlr = cxlr_overlapping_range(dev, ctx->start, ctx->end);
+ if (!cxlr)
+ return 0;
+
+ cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
+ port = cxlrd_to_port(cxlrd);
+ p = &cxlr->params;
+
+ /* Force the region state back to CXL_CONFIG_ACTIVE so that
+ * unregister_region() does not run the full decoder reset path
+ * which would invalidate the decoder programming that HMEM
+ * relies on to create its DAX device and online the underlying
+ * memory.
+ */
+ scoped_guard(rwsem_write, &cxl_rwsem.region)
+ p->state = min(p->state, CXL_CONFIG_ACTIVE);
+
+ devm_release_action(port->uport_dev, unregister_region, cxlr);
+
+ return 0;
+}
+
+void cxl_region_teardown(resource_size_t start, resource_size_t end)
+{
+ struct cxl_range_ctx ctx = { .start = start, .end = end };
+
+ bus_for_each_dev(&cxl_bus_type, NULL, &ctx, cxl_region_teardown_cb);
+}
+EXPORT_SYMBOL_GPL(cxl_region_teardown);
+
static void cxl_region_enable_dax(struct cxl_region *cxlr)
{
struct cxl_region_params *p = &cxlr->params;
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 414ddf6c35d7..a215a88ef59c 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -880,6 +880,7 @@ 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);
void cxl_register_dax(resource_size_t start, resource_size_t end);
+void cxl_region_teardown(resource_size_t start, resource_size_t end);
#else
static inline bool is_cxl_pmem_region(struct device *dev)
{
@@ -911,6 +912,10 @@ static inline void cxl_register_dax(resource_size_t start,
resource_size_t end)
{
}
+static inline void cxl_region_teardown(resource_size_t start,
+ resource_size_t end)
+{
+}
#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 b9312e0f2e62..7d874ee169ac 100644
--- a/drivers/dax/hmem/hmem.c
+++ b/drivers/dax/hmem/hmem.c
@@ -158,8 +158,10 @@ static int handle_deferred_cxl(struct device *host, int target_nid,
if (cxl_regions_fully_map(res->start, res->end)) {
dax_cxl_mode = DAX_CXL_MODE_DROP;
cxl_register_dax(res->start, res->end);
- } else
+ } else {
dax_cxl_mode = DAX_CXL_MODE_REGISTER;
+ cxl_region_teardown(res->start, res->end);
+ }

hmem_register_device(host, target_nid, res);
}
--
2.17.1