thp: mprotect: transparent huge page support

Natively handle huge pmds when changing page tables on behalf of
mprotect().

I left out update_mmu_cache() because we do not need it on x86 anyway but
more importantly the interface works on ptes, not pmds.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 34 insertions, 1 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 37e89a32a0b1..7b55fe0e998b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -948,6 +948,33 @@ int mincore_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
         return ret;
 }
 
+int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
+                unsigned long addr, pgprot_t newprot)
+{
+        struct mm_struct *mm = vma->vm_mm;
+        int ret = 0;
+
+        spin_lock(&mm->page_table_lock);
+        if (likely(pmd_trans_huge(*pmd))) {
+                if (unlikely(pmd_trans_splitting(*pmd))) {
+                        spin_unlock(&mm->page_table_lock);
+                        wait_split_huge_page(vma->anon_vma, pmd);
+                } else {
+                        pmd_t entry;
+
+                        entry = pmdp_get_and_clear(mm, addr, pmd);
+                        entry = pmd_modify(entry, newprot);
+                        set_pmd_at(mm, addr, pmd, entry);
+                        spin_unlock(&vma->vm_mm->page_table_lock);
+                        flush_tlb_range(vma, addr, addr + HPAGE_PMD_SIZE);
+                        ret = 1;
+                }
+        } else
+                spin_unlock(&vma->vm_mm->page_table_lock);
+
+        return ret;
+}
+
 pmd_t *page_check_address_pmd(struct page *page,
                               struct mm_struct *mm,
                               unsigned long address,
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 9402080d0d4a..5a688a2756be 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -88,7 +88,13 @@ static inline void change_pmd_range(struct vm_area_struct *vma, pud_t *pud,
         pmd = pmd_offset(pud, addr);
         do {
                 next = pmd_addr_end(addr, end);
-                split_huge_page_pmd(vma->vm_mm, pmd);
+                if (pmd_trans_huge(*pmd)) {
+                        if (next - addr != HPAGE_PMD_SIZE)
+                                split_huge_page_pmd(vma->vm_mm, pmd);
+                        else if (change_huge_pmd(vma, pmd, addr, newprot))
+                                continue;
+                        /* fall through */
+                }
                 if (pmd_none_or_clear_bad(pmd))
                         continue;
                 change_pte_range(vma->vm_mm, pmd, addr, next, newprot,