[PATCH v3 3/3] acpi,srat: give memory block size advice based on CFMWS alignment

[Gregory Price <gourry@gourry.net>]

Capacity is stranded when CFMWS regions are not aligned to block size.
On x86, block size increases with capacity (2G blocks @ 64G capacity).

Use CFMWS base/size to report memory block size alignment advice.

After the alignment, the acpi code begins populating numa nodes with
memblocks, so probe the value just prior to lock it in.  All future
callers should be providing advice prior to this point.

Suggested-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Gregory Price <gourry@gourry.net>
---
 drivers/acpi/numa/srat.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/drivers/acpi/numa/srat.c b/drivers/acpi/numa/srat.c
index 44f91f2c6c5d..35e6f7c17f60 100644
--- a/drivers/acpi/numa/srat.c
+++ b/drivers/acpi/numa/srat.c
@@ -14,6 +14,7 @@
 #include <linux/errno.h>
 #include <linux/acpi.h>
 #include <linux/memblock.h>
+#include <linux/memory.h>
 #include <linux/numa.h>
 #include <linux/nodemask.h>
 #include <linux/topology.h>
@@ -333,6 +334,29 @@ acpi_parse_memory_affinity(union acpi_subtable_headers *header,
 	return 0;
 }
 
+/* Advise memblock on maximum block size to avoid stranded capacity. */
+static int __init acpi_align_cfmws(union acpi_subtable_headers *header,
+				   void *arg, const unsigned long table_end)
+{
+	struct acpi_cedt_cfmws *cfmws = (struct acpi_cedt_cfmws *)header;
+	u64 start = cfmws->base_hpa;
+	u64 size = cfmws->window_size;
+	unsigned long bz;
+
+	for (bz = SZ_64T; bz >= SZ_256M; bz >>= 1) {
+		if (IS_ALIGNED(start, bz) && IS_ALIGNED(size, bz))
+			break;
+	}
+
+	if (bz >= SZ_256M) {
+		if (memory_block_advise_max_size(bz) < 0)
+			pr_warn("CFMWS: memblock size advise failed\n");
+	} else
+		pr_err("CFMWS: [BIOS BUG] base/size alignment violates spec\n");
+
+	return 0;
+}
+
 static int __init acpi_parse_cfmws(union acpi_subtable_headers *header,
 				   void *arg, const unsigned long table_end)
 {
@@ -545,6 +569,15 @@ int __init acpi_numa_init(void)
 	 * Initialize a fake_pxm as the first available PXM to emulate.
 	 */
 
+	/* Align memblock size to CFMW regions if possible */
+	acpi_table_parse_cedt(ACPI_CEDT_TYPE_CFMWS, acpi_align_cfmws, NULL);
+
+	/*
+	 * Nodes start populating with blocks after this, so probe the max
+	 * block size to prevent it from changing in the future.
+	 */
+	memory_block_probe_max_size();
+
 	/* fake_pxm is the next unused PXM value after SRAT parsing */
 	for (i = 0, fake_pxm = -1; i < MAX_NUMNODES; i++) {
 		if (node_to_pxm_map[i] > fake_pxm)
-- 
2.43.0