mm/hugetlb: charge folios to the target mm's memcg

HugeTLB folios are currently charged to the memcg of the allocating task. 
This gives the wrong result when a userfaultfd handler populates a HugeTLB
VMA that belongs to another process.  The UFFDIO_COPY ioctl operates on
the userfaultfd context's mm, but get_mem_cgroup_from_current() charges
the folio to the handler's memcg instead.

This can be reproduced by placing the faulting process and its userfaultfd
handler in different memory cgroups.  Have the target process register a
HugeTLB mapping with userfaultfd, trigger a missing fault, and let the
handler resolve it with UFFDIO_COPY.  The hugepage usage is then reported
in the handler's memory.current instead of the target's.

The generic userfaultfd population path avoids this problem by charging
folios to dst_vma->vm_mm.

Pass the target mm through hugetlb_alloc_folio() and charge the folio by
using get_mem_cgroup_from_mm().  This preserves the existing charge timing
and error handling while making HugeTLB userfaultfd population consistent
with the generic path.

Link: https://lore.kernel.org/20260903075048.3316-1-zhoujinmeng@bytedance.com
Fixes: 8cba9576df60 ("hugetlb: memcg: account hugetlb-backed memory in memory controller")
Signed-off-by: Jinmeng Zhou <zhoujinmeng@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Reviewed-by: Hongfu Li <lihongfu@kylinos.cn>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: <stable@vger.kernel.org>

2 files changed, 7 insertions, 4 deletions

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 900c95e346b2..80a5a03e9cee 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -694,7 +694,8 @@ enum hugetlb_alloc_flag {
 #define HUGETLB_ALLOC_USE_GLOBAL_RESERVATIONS BIT(HUGETLB_ALLOC_USE_GLOBAL_RESERVATIONS_BIT)
 
 struct folio *hugetlb_alloc_folio(struct hstate *h,
-		struct mempolicy_interpreted *mpoli, u8 alloc_flags);
+		struct mempolicy_interpreted *mpoli, struct mm_struct *mm,
+		u8 alloc_flags);
 struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 				unsigned long addr, bool cow_from_owner);
 struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid,
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index c79992643556..058ebd73ff16 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -647,7 +647,8 @@ static inline int mem_cgroup_charge(struct folio *folio, struct mm_struct *mm,
 	return __mem_cgroup_charge(folio, mm, gfp);
 }
 
-int mem_cgroup_charge_hugetlb(struct folio* folio, gfp_t gfp);
+int mem_cgroup_charge_hugetlb(struct folio *folio, struct mm_struct *mm,
+			      gfp_t gfp);
 
 int mem_cgroup_swapin_charge_folio(struct folio *folio, unsigned short id,
 				   struct mm_struct *mm, gfp_t gfp);
@@ -1146,9 +1147,10 @@ static inline int mem_cgroup_charge(struct folio *folio,
 	return 0;
 }
 
-static inline int mem_cgroup_charge_hugetlb(struct folio* folio, gfp_t gfp)
+static inline int mem_cgroup_charge_hugetlb(struct folio *folio,
+					    struct mm_struct *mm, gfp_t gfp)
 {
-        return 0;
+	return 0;
 }
 
 static inline int mem_cgroup_swapin_charge_folio(struct folio *folio,