mm/hugetlb: make pud_huge() and follow_huge_pud() aware of non-present pud entry

follow_pud_mask() does not support non-present pud entry now.  As long as
I tested on x86_64 server, follow_pud_mask() still simply returns
no_page_table() for non-present_pud_entry() due to pud_bad(), so no severe
user-visible effect should happen.  But generally we should call
follow_huge_pud() for non-present pud entry for 1GB hugetlb page.

Update pud_huge() and follow_huge_pud() to handle non-present pud entries.
The changes are similar to previous works for pud entries commit
e66f17ff7177 ("mm/hugetlb: take page table lock in follow_huge_pmd()") and
commit cbef8478bee5 ("mm/hugetlb: pmd_huge() returns true for non-present
hugepage").

Link: https://lkml.kernel.org/r/20220714042420.1847125-3-naoya.horiguchi@linux.dev
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Liu Shixin <liushixin2@huawei.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
index 509408da0da1e2d095c6818b6fe4b4b1e9682dc5..6b3033845c6d321818ed47c31470a2d9222c1538 100644 (file)
--- a/arch/x86/mm/hugetlbpage.c
+++ b/arch/x86/mm/hugetlbpage.c
@@ -30,9 +30,15 @@ int pmd_huge(pmd_t pmd)
                (pmd_val(pmd) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
 }
 
+/*
+ * pud_huge() returns 1 if @pud is hugetlb related entry, that is normal
+ * hugetlb entry or non-present (migration or hwpoisoned) hugetlb entry.
+ * Otherwise, returns 0.
+ */
 int pud_huge(pud_t pud)
 {
-       return !!(pud_val(pud) & _PAGE_PSE);
+       return !pud_none(pud) &&
+               (pud_val(pud) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
 }
 
 #ifdef CONFIG_HUGETLB_PAGE

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ee6655e47213f7b547b698fb880013508a0f0aeb..9b79806be17bbac69d00827ef133b72ee6a6f22c 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6985,10 +6985,38 @@ struct page * __weak
 follow_huge_pud(struct mm_struct *mm, unsigned long address,
                pud_t *pud, int flags)
 {
-       if (flags & (FOLL_GET | FOLL_PIN))
+       struct page *page = NULL;
+       spinlock_t *ptl;
+       pte_t pte;
+
+       if (WARN_ON_ONCE(flags & FOLL_PIN))
                return NULL;
 
-       return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
+retry:
+       ptl = huge_pte_lock(hstate_sizelog(PUD_SHIFT), mm, (pte_t *)pud);
+       if (!pud_huge(*pud))
+               goto out;
+       pte = huge_ptep_get((pte_t *)pud);
+       if (pte_present(pte)) {
+               page = pud_page(*pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT);
+               if (WARN_ON_ONCE(!try_grab_page(page, flags))) {
+                       page = NULL;
+                       goto out;
+               }
+       } else {
+               if (is_hugetlb_entry_migration(pte)) {
+                       spin_unlock(ptl);
+                       __migration_entry_wait(mm, (pte_t *)pud, ptl);
+                       goto retry;
+               }
+               /*
+                * hwpoisoned entry is treated as no_page_table in
+                * follow_page_mask().
+                */
+       }
+out:
+       spin_unlock(ptl);
+       return page;
 }
 
 struct page * __weak