[PATCH 4/6] dax/hmem: Defer Soft Reserved overlap handling until CXL region assembly completes

[Smita Koralahalli <Smita.KoralahalliChannabasappa@xxxxxxx>]

Previously, dax_hmem deferred to CXL only when an immediate resource
intersection with a CXL window was detected. This left a gap: if cxl_acpi
or cxl_pci probing or region assembly had not yet started, hmem could
prematurely claim ranges.

Fix this by introducing a dax_cxl_mode state machine and a deferred
work mechanism.

The new workqueue delays consideration of Soft Reserved overlaps until
the CXL subsystem has had a chance to complete its discovery and region
assembly. This avoids premature iomem claims, eliminates race conditions
with async cxl_pci probe, and provides a cleaner handoff between hmem and
CXL resource management.

Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@xxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 drivers/dax/hmem/hmem.c | 72 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 70 insertions(+), 2 deletions(-)

diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c
index 7ada820cb177..90978518e5f4 100644
--- a/drivers/dax/hmem/hmem.c
+++ b/drivers/dax/hmem/hmem.c
@@ -58,9 +58,45 @@ static void release_hmem(void *pdev)
 	platform_device_unregister(pdev);
 }
 
+static enum dax_cxl_mode {
+	DAX_CXL_MODE_DEFER,
+	DAX_CXL_MODE_REGISTER,
+	DAX_CXL_MODE_DROP,
+} dax_cxl_mode;
+
+static int handle_deferred_cxl(struct device *host, int target_nid,
+				const struct resource *res)
+{
+	if (region_intersects(res->start, resource_size(res), IORESOURCE_MEM,
+			      IORES_DESC_CXL) != REGION_DISJOINT) {
+		if (dax_cxl_mode == DAX_CXL_MODE_DROP)
+			dev_dbg(host, "dropping CXL range: %pr\n", res);
+	}
+	return 0;
+}
+
+struct dax_defer_work {
+	struct platform_device *pdev;
+	struct work_struct work;
+};
+
+static void process_defer_work(struct work_struct *_work)
+{
+	struct dax_defer_work *work = container_of(_work, typeof(*work), work);
+	struct platform_device *pdev = work->pdev;
+
+	/* relies on cxl_acpi and cxl_pci having had a chance to load */
+	wait_for_device_probe();
+
+	dax_cxl_mode = DAX_CXL_MODE_DROP;
+
+	walk_hmem_resources(&pdev->dev, handle_deferred_cxl);
+}
+
 static int hmem_register_device(struct device *host, int target_nid,
 				const struct resource *res)
 {
+	struct dax_defer_work *work = dev_get_drvdata(host);
 	struct platform_device *pdev;
 	struct memregion_info info;
 	long id;
@@ -69,8 +105,18 @@ static int hmem_register_device(struct device *host, int target_nid,
 	if (IS_ENABLED(CONFIG_DEV_DAX_CXL) &&
 	    region_intersects(res->start, resource_size(res), IORESOURCE_MEM,
 			      IORES_DESC_CXL) != REGION_DISJOINT) {
-		dev_dbg(host, "deferring range to CXL: %pr\n", res);
-		return 0;
+		switch (dax_cxl_mode) {
+		case DAX_CXL_MODE_DEFER:
+			dev_dbg(host, "deferring range to CXL: %pr\n", res);
+			schedule_work(&work->work);
+			return 0;
+		case DAX_CXL_MODE_REGISTER:
+			dev_dbg(host, "registering CXL range: %pr\n", res);
+			break;
+		case DAX_CXL_MODE_DROP:
+			dev_dbg(host, "dropping CXL range: %pr\n", res);
+			return 0;
+		}
 	}
 
 #ifdef CONFIG_EFI_SOFT_RESERVE
@@ -130,8 +176,30 @@ static int hmem_register_device(struct device *host, int target_nid,
 	return rc;
 }
 
+static void kill_defer_work(void *_work)
+{
+	struct dax_defer_work *work = container_of(_work, typeof(*work), work);
+
+	cancel_work_sync(&work->work);
+	kfree(work);
+}
+
 static int dax_hmem_platform_probe(struct platform_device *pdev)
 {
+	struct dax_defer_work *work = kzalloc(sizeof(*work), GFP_KERNEL);
+	int rc;
+
+	if (!work)
+		return -ENOMEM;
+
+	work->pdev = pdev;
+	INIT_WORK(&work->work, process_defer_work);
+
+	rc = devm_add_action_or_reset(&pdev->dev, kill_defer_work, work);
+	if (rc)
+		return rc;
+
+	platform_set_drvdata(pdev, work);
 	return walk_hmem_resources(&pdev->dev, hmem_register_device);
 }
 
-- 
2.17.1