mm: hugetlb_vmemmap: disable hugetlb_optimize_vmemmap when struct page crosses page boundaries

Patch series "add hugetlb_optimize_vmemmap sysctl", v11.

This series aims to add hugetlb_optimize_vmemmap sysctl to enable or
disable the feature of optimizing vmemmap pages associated with HugeTLB
pages.


This patch (of 4):

If the size of "struct page" is not the power of two but with the feature
of minimizing overhead of struct page associated with each HugeTLB is
enabled, then the vmemmap pages of HugeTLB will be corrupted after
remapping (panic is about to happen in theory).  But this only exists when
!CONFIG_MEMCG && !CONFIG_SLUB on x86_64.  However, it is not a
conventional configuration nowadays.  So it is not a real word issue, just
the result of a code review.

But we cannot prevent anyone from configuring that combined configure. 
This hugetlb_optimize_vmemmap should be disable in this case to fix this
issue.

Link: https://lkml.kernel.org/r/20220512041142.39501-1-songmuchun@bytedance.com
Link: https://lkml.kernel.org/r/20220512041142.39501-2-songmuchun@bytedance.comSigned-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kees Cook <keescook@chromium.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/hugetlb_vmemmap.c

@@ -28,12 +28,6 @@ EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);
 
 static int __init hugetlb_vmemmap_early_param(char *buf)
 {
-	/* We cannot optimize if a "struct page" crosses page boundaries. */
-	if (!is_power_of_2(sizeof(struct page))) {
-		pr_warn("cannot free vmemmap pages because \"struct page\" crosses page boundaries\n");
-		return 0;
-	}
-
 	if (!buf)
 		return -EINVAL;
 
@@ -119,6 +113,12 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
 	if (!hugetlb_optimize_vmemmap_enabled())
 		return;
 
+	if (!is_power_of_2(sizeof(struct page))) {
+		pr_warn_once("cannot optimize vmemmap pages because \"struct page\" crosses page boundaries\n");
+		static_branch_disable(&hugetlb_optimize_vmemmap_key);
+		return;
+	}
+
 	vmemmap_pages = (nr_pages * sizeof(struct page)) >> PAGE_SHIFT;
 	/*
 	 * The head page is not to be freed to buddy allocator, the other tail