linux-kernel - [PATCH v2] dax/kmem: Pass valid argument to memory_group_register

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Message-Id: <20230621103411.113030-1-tsahu@linux.ibm.com>
Date:   Wed, 21 Jun 2023 16:04:11 +0530
From:   Tarun Sahu <tsahu@...ux.ibm.com>
To:     nvdimm@...ts.linux.dev, linux-cxl@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, dave.jiang@...el.com,
        dan.j.williams@...el.com, vishal.l.verma@...el.com,
        aneesh.kumar@...ux.ibm.com, jaypatel@...ux.ibm.com,
        tsahu@...ux.ibm.com
Subject: [PATCH v2] dax/kmem: Pass valid argument to memory_group_register_static

memory_group_register_static takes maximum number of pages as the argument
while dev_dax_kmem_probe passes total_len (in bytes) as the argument.

IIUC, I don't see any crash/panic impact as such. As,
memory_group_register_static just set the max_pages limit which is used in
auto_movable_zone_for_pfn to determine the zone.

which might cause these condition to behave differently,

This will be true always so jump will happen to kernel_zone
	if (!auto_movable_can_online_movable(NUMA_NO_NODE, group, nr_pages))
		goto kernel_zone;
---
kernel_zone:
	return default_kernel_zone_for_pfn(nid, pfn, nr_pages);

---

Here, In below, zone_intersects compare range will be larger as nr_pages
will be higher (derived from total_len passed in dev_dax_kmem_probe).

static struct zone *default_kernel_zone_for_pfn(int nid, unsigned long start_pfn,
		unsigned long nr_pages)
{
	struct pglist_data *pgdat = NODE_DATA(nid);
	int zid;

	for (zid = 0; zid < ZONE_NORMAL; zid++) {
		struct zone *zone = &pgdat->node_zones[zid];

		if (zone_intersects(zone, start_pfn, nr_pages))
			return zone;
	}

	return &pgdat->node_zones[ZONE_NORMAL];
}

Incorrect zone will be returned here, which in later time might cause bigger
problem.

Fixes: eedf634aac3b ("dax/kmem: use a single static memory group for a single probed unit")
Signed-off-by: Tarun Sahu <tsahu@...ux.ibm.com>
Reviewed-by: Vishal Verma <vishal.l.verma@...el.com>
---
 drivers/dax/kmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index 7b36db6f1cbd..898ca9505754 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -99,7 +99,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 	if (!data->res_name)
 		goto err_res_name;
 
-	rc = memory_group_register_static(numa_node, total_len);
+	rc = memory_group_register_static(numa_node, PFN_UP(total_len));
 	if (rc < 0)
 		goto err_reg_mgid;
 	data->mgid = rc;
-- 
2.31.1