[RFC,1/2] x86/mm: if memblock size is adjusted, update the cached value

Commit Message

Gregory Price Sept. 25, 2024, 4:52 a.m. UTC

When parsing CFMWS, we need to know the current block size expected
to avoid accidentally adjusting the size upward. This causes a value
to be cached in a static global.  Update the static global if the
value is subsequently updated.

Print a warning that this has occurred for debugging purposes if
blocksize is changed at an unexpected time.

Signed-off-by: Gregory Price <[e-mail]>
---
 arch/x86/mm/init_64.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

Patch

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index ff253648706f..0db7ce11e5c5 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1424,6 +1424,7 @@  void mark_rodata_ro(void)
 
 /* Adjustable memory block size */
 static unsigned long set_memory_block_size;
+static unsigned long memory_block_size_probed;
 int __init set_memory_block_size_order(unsigned int order)
 {
 	unsigned long size = 1UL << order;
@@ -1432,6 +1433,19 @@  int __init set_memory_block_size_order(unsigned int order)
 		return -EINVAL;
 
 	set_memory_block_size = size;
+
+	/*
+	 * If the block size has already been probed, we need to change it.
+	 * This can happen during ACPI/CFMWS parsing, since it needs to
+	 * probe the system for the existing block size to avoid increasing
+	 * the block size if lower memory happens to be misaligned
+	 */
+	if (memory_block_size_probed) {
+		memory_block_size_probed = size;
+		pr_warn("x86/mm: Memory block size changed: %ldMB\n",
+			size >> 20);
+	}
+
 	return 0;
 }
 
@@ -1471,7 +1485,6 @@  static unsigned long probe_memory_block_size(void)
 	return bz;
 }
 
-static unsigned long memory_block_size_probed;
 unsigned long memory_block_size_bytes(void)
 {
 	if (!memory_block_size_probed)