diff mbox series

[v3] DAX: warn when kmem regions are truncated for memory block alignment.

Message ID 20250410142831.217887-1-gourry@gourry.net
State New
Headers show
Series [v3] DAX: warn when kmem regions are truncated for memory block alignment. | expand

Commit Message

Gregory Price April 10, 2025, 2:28 p.m. UTC 
Device capacity intended for use as system ram should be aligned to the
architecture-defined memory block size or that capacity will be silently
truncated and capacity stranded.

As hotplug dax memory becomes more prevelant, the memory block size
alignment becomes more important for platform and device vendors to
pay attention to - so this truncation should not be silent.

This issue is particularly relevant for CXL Dynamic Capacity devices,
whose capacity may arrive in spec-aligned but block-misaligned chunks.

Suggested-by: David Hildenbrand <david@redhat.com>
Suggested-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Gregory Price <gourry@gourry.net>
---
 drivers/dax/kmem.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index e97d47f42ee2..584c70a34b52 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -13,6 +13,7 @@ 
 #include <linux/mman.h>
 #include <linux/memory-tiers.h>
 #include <linux/memory_hotplug.h>
+#include <linux/string_helpers.h>
 #include "dax-private.h"
 #include "bus.h"
 
@@ -68,7 +69,7 @@  static void kmem_put_memory_types(void)
 static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 {
 	struct device *dev = &dev_dax->dev;
-	unsigned long total_len = 0;
+	unsigned long total_len = 0, orig_len = 0;
 	struct dax_kmem_data *data;
 	struct memory_dev_type *mtype;
 	int i, rc, mapped = 0;
@@ -97,6 +98,7 @@  static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 	for (i = 0; i < dev_dax->nr_range; i++) {
 		struct range range;
 
+		orig_len += range_len(&dev_dax->ranges[i].range);
 		rc = dax_kmem_range(dev_dax, i, &range);
 		if (rc) {
 			dev_info(dev, "mapping%d: %#llx-%#llx too small after alignment\n",
@@ -109,6 +111,12 @@  static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 	if (!total_len) {
 		dev_warn(dev, "rejecting DAX region without any memory after alignment\n");
 		return -EINVAL;
+	} else if (total_len != orig_len) {
+		char buf[16];
+
+		string_get_size(orig_len - total_len, 1, STRING_UNITS_2,
+				buf, sizeof(buf));
+		dev_warn(dev, "DAX region truncated by %s due to alignment\n", buf);
 	}
 
 	init_node_memory_type(numa_node, mtype);