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

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Message-ID: <20240925045242.3735-1-gourry@gourry.net>
Date: Wed, 25 Sep 2024 00:52:41 -0400
From: Gregory Price <gourry@...rry.net>
To: linux-acpi@...r.kernel.org,
	x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	dave.hansen@...ux.intel.com,
	luto@...nel.org,
	peterz@...radead.org,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	hpa@...or.com,
	rafael@...nel.org,
	lenb@...nel.org,
	dan.j.williams@...el.com,
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	rrichter@....com,
	ytcoode@...il.com,
	gourry@...rry.net,
	dave.jiang@...el.com,
	haibo1.xu@...el.com
Subject: [RFC PATCH 1/2] x86/mm: if memblock size is adjusted, update the cached value

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 <gourry@...rry.net>
---
 arch/x86/mm/init_64.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

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)
-- 
2.43.0