mm: pvmw: add support for walking devmap pages

The devmap pages can not use page_vma_mapped_walk() to check if a huge
devmap page is mapped into a vma.  Add support for walking huge devmap
pages so that DAX can use it in the next patch.

Link: https://lkml.kernel.org/r/20220403053957.10770-5-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ross Zwisler <zwisler@kernel.org>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Cc: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 14a5cda..c10f839 100644 (file)
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -210,16 +210,10 @@ restart:
                 */
                pmde = READ_ONCE(*pvmw->pmd);
 
-               if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
+               if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde) ||
+                   (pmd_present(pmde) && pmd_devmap(pmde))) {
                        pvmw->ptl = pmd_lock(mm, pvmw->pmd);
                        pmde = *pvmw->pmd;
-                       if (likely(pmd_trans_huge(pmde))) {
-                               if (pvmw->flags & PVMW_MIGRATION)
-                                       return not_found(pvmw);
-                               if (!check_pmd(pmd_pfn(pmde), pvmw))
-                                       return not_found(pvmw);
-                               return true;
-                       }
                        if (!pmd_present(pmde)) {
                                swp_entry_t entry;
 
@@ -232,6 +226,13 @@ restart:
                                        return not_found(pvmw);
                                return true;
                        }
+                       if (likely(pmd_trans_huge(pmde) || pmd_devmap(pmde))) {
+                               if (pvmw->flags & PVMW_MIGRATION)
+                                       return not_found(pvmw);
+                               if (!check_pmd(pmd_pfn(pmde), pvmw))
+                                       return not_found(pvmw);
+                               return true;
+                       }
                        /* THP pmd was split under us: handle on pte level */
                        spin_unlock(pvmw->ptl);
                        pvmw->ptl = NULL;