mm/rmap: introduce and use hugetlb_try_dup_anon_rmap()

hugetlb rmap handling differs quite a lot from "ordinary" rmap code.  For
example, hugetlb currently only supports entire mappings, and treats any
mapping as mapped using a single "logical PTE".  Let's move it out of the
way so we can overhaul our "ordinary" rmap.  implementation/interface.

So let's introduce and use hugetlb_try_dup_anon_rmap() to make all hugetlb
handling use dedicated hugetlb_* rmap functions.

Add sanity checks that we end up with the right folios in the right
functions.

Note that is_device_private_page() does not apply to hugetlb.

Link: https://lkml.kernel.org/r/20231220224504.646757-5-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2563ffdb51bc7154cd052d26d735ea74f6eea1db..75bba6102825676dad3363b7f8370970b8bf0baa 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1964,15 +1964,21 @@ static inline bool page_maybe_dma_pinned(struct page *page)
  *
  * The caller has to hold the PT lock and the vma->vm_mm->->write_protect_seq.
  */
-static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
-                                         struct page *page)
+static inline bool folio_needs_cow_for_dma(struct vm_area_struct *vma,
+                                         struct folio *folio)
 {
        VM_BUG_ON(!(raw_read_seqcount(&vma->vm_mm->write_protect_seq) & 1));
 
        if (!test_bit(MMF_HAS_PINNED, &vma->vm_mm->flags))
                return false;
 
-       return page_maybe_dma_pinned(page);
+       return folio_maybe_dma_pinned(folio);
+}
+
+static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
+                                         struct page *page)
+{
+       return folio_needs_cow_for_dma(vma, page_folio(page));
 }
 
 /**

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 56900a16f41a6a67e3fe4b4b30477e5e097ac855..5f26752de945c686e707e483689e8b8707e88460 100644 (file)
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -211,6 +211,22 @@ void hugetlb_add_anon_rmap(struct folio *, struct vm_area_struct *,
 void hugetlb_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
                unsigned long address);
 
+/* See page_try_dup_anon_rmap() */
+static inline int hugetlb_try_dup_anon_rmap(struct folio *folio,
+               struct vm_area_struct *vma)
+{
+       VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);
+       VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);
+
+       if (PageAnonExclusive(&folio->page)) {
+               if (unlikely(folio_needs_cow_for_dma(vma, folio)))
+                       return -EBUSY;
+               ClearPageAnonExclusive(&folio->page);
+       }
+       atomic_inc(&folio->_entire_mapcount);
+       return 0;
+}
+
 static inline void hugetlb_add_file_rmap(struct folio *folio)
 {
        VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);
@@ -228,6 +244,8 @@ static inline void hugetlb_remove_rmap(struct folio *folio)
 
 static inline void __page_dup_rmap(struct page *page, bool compound)
 {
+       VM_WARN_ON(folio_test_hugetlb(page_folio(page)));
+
        if (compound) {
                struct folio *folio = (struct folio *)page;
 

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 57e898187931442e906c3e7308654f77353e9867..378e460a6ab41dc5592f24cb4cd76981ccfbdea6 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5409,8 +5409,7 @@ again:
                         */
                        if (!folio_test_anon(pte_folio)) {
                                hugetlb_add_file_rmap(pte_folio);
-                       } else if (page_try_dup_anon_rmap(&pte_folio->page,
-                                                         true, src_vma)) {
+                       } else if (hugetlb_try_dup_anon_rmap(pte_folio, src_vma)) {
                                pte_t src_pte_old = entry;
                                struct folio *new_folio;