mm/hugetlb: deal with multiple calls to hugetlb_bootmem_alloc

Architectures that want pre-HVO of hugetlb vmemmap pages will need to call
hugetlb_bootmem_alloc from an earlier spot in boot (before sparse_init).
To facilitate some architectures doing this, protect hugetlb_bootmem_alloc
against multiple calls.

Also provide a helper function to check if it's been called, so that the
early HVO code, to be added later, can see if there is anything to do.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Frank van der Linden <[e-mail]>
Cc: Alexander Gordeev <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Dan Carpenter <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Joao Martins <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Madhavan Srinivasan <[e-mail]>
Cc: Michael Ellerman <[e-mail]>
Cc: Muchun Song <[e-mail]>
Cc: Oscar Salvador <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Roman Gushchin (Cruise) <[e-mail]>
Cc: Usama Arif <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Cc: Yu Zhao <[e-mail]>
Cc: Zi Yan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/hugetlb.h

···
 extern struct list_head huge_boot_pages[MAX_NUMNODES];
 
 void hugetlb_bootmem_alloc(void);
+bool hugetlb_bootmem_allocated(void);
 
 /* arch callbacks */
 
···
 
 static inline void hugetlb_bootmem_alloc(void)
 {
+}
+
+static inline bool hugetlb_bootmem_allocated(void)
+{
+	return false;
 }
 #endif	/* CONFIG_HUGETLB_PAGE */
 

mm/hugetlb.c

···
 }
 hugetlb_early_param("default_hugepagesz", default_hugepagesz_setup);
 
+static bool __hugetlb_bootmem_allocated __initdata;
+
+bool __init hugetlb_bootmem_allocated(void)
+{
+	return __hugetlb_bootmem_allocated;
+}
+
 void __init hugetlb_bootmem_alloc(void)
 {
 	struct hstate *h;
+
+	if (__hugetlb_bootmem_allocated)
+		return;
 
 	hugetlb_parse_params();
 
···
 		if (hstate_is_gigantic(h))
 			hugetlb_hstate_alloc_pages(h);
 	}
+
+	__hugetlb_bootmem_allocated = true;
 }
 
 static unsigned int allowed_mems_nr(struct hstate *h)