[PATCH 20/23] hugetlb/userfaultfd: Allow wr-protect none ptes

Peter Xu
2021-03-23T00:51:52Z

Teach hugetlbfs code to wr-protect none ptes just in case the page cache
existed for that pte. Meanwhile we also need to be able to recognize a uffd-wp
marker pte and remove it for uffd_wp_resolve.

Since at it, introduce a variable "psize" to replace all references to the huge
page size fetcher.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
mm/hugetlb.c | 29 +++++++++++++++++++++++++----
1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 448ef745d5ee..d4acf9d9d087 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5110,7 +5110,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
pte_t *ptep;
pte_t pte;
struct hstate *h = hstate_vma(vma);
- unsigned long pages = 0;
+ unsigned long pages = 0, psize = huge_page_size(h);
bool shared_pmd = false;
struct mmu_notifier_range range;
bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
@@ -5130,13 +5130,19 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,

mmu_notifier_invalidate_range_start(&range);
i_mmap_lock_write(vma->vm_file->f_mapping);
- for (; address < end; address += huge_page_size(h)) {
+ for (; address < end; address += psize) {
spinlock_t *ptl;
- ptep = huge_pte_offset(mm, address, huge_page_size(h));
+ ptep = huge_pte_offset(mm, address, psize);
if (!ptep)
continue;
ptl = huge_pte_lock(h, mm, ptep);
if (huge_pmd_unshare(mm, vma, &address, ptep)) {
+ /*
+ * When uffd-wp is enabled on the vma, unshare
+ * shouldn't happen at all. Warn about it if it
+ * happened due to some reason.
+ */
+ WARN_ON_ONCE(uffd_wp || uffd_wp_resolve);
pages++;
spin_unlock(ptl);
shared_pmd = true;
@@ -5160,12 +5166,21 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
else if (uffd_wp_resolve)
newpte = pte_swp_clear_uffd_wp(newpte);
set_huge_swap_pte_at(mm, address, ptep,
- newpte, huge_page_size(h));
+ newpte, psize);
pages++;
}
spin_unlock(ptl);
continue;
}
+ if (unlikely(is_swap_special_pte(pte))) {
+ WARN_ON_ONCE(!pte_swp_uffd_wp_special(pte));
+ /*
+ * This is changing a non-present pte into a none pte,
+ * no need for huge_ptep_modify_prot_start/commit().
+ */
+ if (uffd_wp_resolve)
+ huge_pte_clear(mm, address, ptep, psize);
+ }
if (!huge_pte_none(pte)) {
pte_t old_pte;

@@ -5178,6 +5193,12 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
pte = huge_pte_clear_uffd_wp(pte);
huge_ptep_modify_prot_commit(vma, address, ptep, old_pte, pte);
pages++;
+ } else {
+ /* None pte */
+ if (unlikely(uffd_wp))
+ /* Safe to modify directly (none->non-present). */
+ set_huge_pte_at(mm, address, ptep,
+ pte_swp_mkuffd_wp_special(vma));
}
spin_unlock(ptl);
}
--
2.26.2