mm/mmap: teach generic_get_unmapped_area{_topdown} to handle hugetlb mappings

Patch series "Unify hugetlb into arch_get_unmapped_area functions", v4.

This is an attempt to get rid of a fair amount of duplicated code wrt. 
hugetlb and *get_unmapped_area* functions.

HugeTLB registers a .get_unmapped_area function which gets called from
__get_unmapped_area().
hugetlb_get_unmapped_area() is defined by a bunch of architectures and
it also has a generic definition for those that do not define it.
Short-long story is that there is a ton of duplicated code between
specific hugetlb *_get_unmapped_area_* functions and mm-core functions,
so we can do better by teaching arch_get_unmapped_area* functions how
to deal with hugetlb mappings.

Note that not a lot of things need to be taught though. 
hugetlb_get_unmapped_area, that gets called for hugetlb mappings, runs
some sanity checks prior to calling mm_get_unmapped_area_vmflags(), so we
do not need to that down the road in the respective
{generic,arch}_get_unmapped_area* functions.

More information can be found in the respective patches.

LTP mmapstress hugetlb selftests were ran succesfully on:


This patch (of 9):

We want to stop special casing hugetlb mappings and make them go through
generic channels, so teach generic_get_unmapped_area{_topdown} to handle
those.  The main difference is that we set info.align_mask for huge
mappings.

Link: https://lkml.kernel.org/r/20241007075037.267650-1-osalvador@suse.de
Link: https://lkml.kernel.org/r/20241007075037.267650-2-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Donet Tom <donettom@linux.ibm.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: osalvadorvilardaga

Diff for: include/linux/hugetlb.h

@@ -1035,9 +1035,19 @@ void hugetlb_unregister_node(struct node *node);
  */
 bool is_raw_hwpoison_page_in_hugepage(struct page *page);
 
+static inline unsigned long huge_page_mask_align(struct file *file)
+{
+	return PAGE_MASK & ~huge_page_mask(hstate_file(file));
+}
+
 #else	/* CONFIG_HUGETLB_PAGE */
 struct hstate {};
 
+static inline unsigned long huge_page_mask_align(struct file *file)
+{
+	return 0;
+}
+
 static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio)
 {
 	return NULL;

Diff for: mm/mmap.c

@@ -776,6 +776,8 @@ generic_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.low_limit = mm->mmap_base;
 	info.high_limit = mmap_end;
 	info.start_gap = stack_guard_placement(vm_flags);
+	if (filp && is_file_hugepages(filp))
+		info.align_mask = huge_page_mask_align(filp);
 	return vm_unmapped_area(&info);
 }
 
@@ -826,6 +828,8 @@ generic_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
 	info.low_limit = PAGE_SIZE;
 	info.high_limit = arch_get_mmap_base(addr, mm->mmap_base);
 	info.start_gap = stack_guard_placement(vm_flags);
+	if (filp && is_file_hugepages(filp))
+		info.align_mask = huge_page_mask_align(filp);
 	addr = vm_unmapped_area(&info);
 
 	/*