linux-kernel - [PATCH v2 5/7] mm,memory_hotplug: Enforce pageblock alignment when memmap_on

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Date:   Tue,  9 Feb 2021 14:38:52 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...nel.org>, VlastimilBabkavbabka@...e.cz,
        pasha.tatashin@...een.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Anshuman Khandual <anshuman.khandual@....com>,
        Oscar Salvador <osalvador@...e.de>
Subject: [PATCH v2 5/7] mm,memory_hotplug: Enforce pageblock alignment when memmap_on_memory

Many places expects us to pass a pageblock aligned range.
E.g: memmap_init_zone() needs a pageblock aligned range in order
to set the proper migrate type for it.
online_pages() needs to operate on a pageblock aligned range for
isolation purposes.

Make sure we disable the feature in case we cannot guarantee the
right alignment.

Signed-off-by: Oscar Salvador <osalvador@...e.de>
---
 mm/memory_hotplug.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index d3fb036d33fd..1a4d5dd1a2c8 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -56,12 +56,16 @@ static int memmap_on_memory_show(char *buffer, const struct kernel_param *kp)
 static __meminit int memmap_on_memory_store(const char *val,
 					    const struct kernel_param *kp)
 {
+	unsigned long pageblock_size = PFN_PHYS(pageblock_nr_pages);
+
 	/*
 	 * Fail silently in case we cannot enable it due to system constraints.
 	 * User can always check whether it is enabled or not via /sys/module.
 	 */
 	if (!IS_ENABLED(CONFIG_ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE) ||
-	    (PMD_SIZE % sizeof(struct page)))
+	    (PMD_SIZE % sizeof(struct page)) ||
+	    !(MIN_MEMORY_BLOCK_SIZE - PMD_SIZE) ||
+	    !(MIN_MEMORY_BLOCK_SIZE - PMD_SIZE) % pageblock_size)
 		return 0;
 
 	return param_set_bool(val, kp);
-- 
2.16.3