linux-kernel - [PATCH v9 4/9] memblock: Unpreserve memory in case of error

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Message-ID: <20251101142325.1326536-5-pasha.tatashin@soleen.com>
Date: Sat,  1 Nov 2025 10:23:20 -0400
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: akpm@...ux-foundation.org,
	brauner@...nel.org,
	corbet@....net,
	graf@...zon.com,
	jgg@...pe.ca,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	linux-mm@...ck.org,
	masahiroy@...nel.org,
	ojeda@...nel.org,
	pasha.tatashin@...een.com,
	pratyush@...nel.org,
	rdunlap@...radead.org,
	rppt@...nel.org,
	tj@...nel.org,
	yanjun.zhu@...ux.dev
Subject: [PATCH v9 4/9] memblock: Unpreserve memory in case of error

If there is an error half way through KHO memory preservation, we should
rollback and unpreserve everything that is partially preserved.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
Suggested-by: Pratyush Yadav <pratyush@...nel.org>
---
 mm/memblock.c | 73 ++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 58 insertions(+), 15 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index e3bef9b35d63..f527ad1ca682 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -2445,29 +2445,60 @@ int reserve_mem_release_by_name(const char *name)
 #define MEMBLOCK_KHO_NODE_COMPATIBLE "memblock-v1"
 #define RESERVE_MEM_KHO_NODE_COMPATIBLE "reserve-mem-v1"
 
+static int __init reserved_mem_preserve(void)
+{
+	unsigned int nr_preserved = 0;
+	int err;
+
+	for (unsigned int i = 0; i < reserved_mem_count; i++, nr_preserved++) {
+		struct reserve_mem_table *map = &reserved_mem_table[i];
+		struct page *page = phys_to_page(map->start);
+		unsigned int nr_pages = map->size >> PAGE_SHIFT;
+
+		err = kho_preserve_pages(page, nr_pages);
+		if (err)
+			goto err_unpreserve;
+	}
+
+	return 0;
+
+err_unpreserve:
+	for (unsigned int i = 0; i < nr_preserved; i++) {
+		struct reserve_mem_table *map = &reserved_mem_table[i];
+		struct page *page = phys_to_page(map->start);
+		unsigned int nr_pages = map->size >> PAGE_SHIFT;
+
+		kho_unpreserve_pages(page, nr_pages);
+	}
+
+	return err;
+}
+
 static int __init prepare_kho_fdt(void)
 {
-	int err = 0, i;
 	struct page *fdt_page;
 	void *fdt;
+	int err;
 
 	fdt_page = alloc_page(GFP_KERNEL);
-	if (!fdt_page)
-		return -ENOMEM;
+	if (!fdt_page) {
+		err = -ENOMEM;
+		goto err_no_fdt_page;
+	}
 
 	fdt = page_to_virt(fdt_page);
+	err = kho_preserve_pages(fdt_page, 1);
+	if (err)
+		goto err_free_fdt;
 
 	err |= fdt_create(fdt, PAGE_SIZE);
 	err |= fdt_finish_reservemap(fdt);
-
 	err |= fdt_begin_node(fdt, "");
 	err |= fdt_property_string(fdt, "compatible", MEMBLOCK_KHO_NODE_COMPATIBLE);
-	for (i = 0; i < reserved_mem_count; i++) {
+
+	for (unsigned int i = 0; !err && i < reserved_mem_count; i++) {
 		struct reserve_mem_table *map = &reserved_mem_table[i];
-		struct page *page = phys_to_page(map->start);
-		unsigned int nr_pages = map->size >> PAGE_SHIFT;
 
-		err |= kho_preserve_pages(page, nr_pages);
 		err |= fdt_begin_node(fdt, map->name);
 		err |= fdt_property_string(fdt, "compatible", RESERVE_MEM_KHO_NODE_COMPATIBLE);
 		err |= fdt_property(fdt, "start", &map->start, sizeof(map->start));
@@ -2477,15 +2508,27 @@ static int __init prepare_kho_fdt(void)
 	err |= fdt_end_node(fdt);
 	err |= fdt_finish(fdt);
 
-	err |= kho_preserve_folio(page_folio(fdt_page));
+	if (err)
+		goto err_unpreserve_fdt;
 
-	if (!err)
-		err = kho_add_subtree(MEMBLOCK_KHO_FDT, fdt);
+	err = kho_add_subtree(MEMBLOCK_KHO_FDT, fdt);
+	if (err)
+		goto err_unpreserve_fdt;
 
-	if (err) {
-		pr_err("failed to prepare memblock FDT for KHO: %d\n", err);
-		put_page(fdt_page);
-	}
+	err = reserved_mem_preserve();
+	if (err)
+		goto err_remove_subtree;
+
+	return 0;
+
+err_remove_subtree:
+	kho_remove_subtree(fdt);
+err_unpreserve_fdt:
+	kho_unpreserve_pages(fdt_page, 1);
+err_free_fdt:
+	put_page(fdt_page);
+err_no_fdt_page:
+	pr_err("failed to prepare memblock FDT for KHO: %d\n", err);
 
 	return err;
 }
-- 
2.51.1.930.gacf6e81ea2-goog