[PATCH 16/23] hugetlb/userfaultfd: Take care of UFFDIO_COPY_MODE_WP

Peter Xu
2021-03-23T00:51:20Z

Firstly, pass the wp_copy variable into hugetlb_mcopy_atomic_pte() thoughout
the stack. Then, apply the UFFD_WP bit if UFFDIO_COPY_MODE_WP is with
UFFDIO_COPY. Introduce huge_pte_mkuffd_wp() for it.

Note that similar to how we've handled shmem, we'd better keep setting the
dirty bit even if UFFDIO_COPY_MODE_WP is provided, so that the core mm will
know this page contains valid data and never drop it.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
include/asm-generic/hugetlb.h | 5 +++++
include/linux/hugetlb.h | 6 ++++--
mm/hugetlb.c | 22 +++++++++++++++++-----
mm/userfaultfd.c | 12 ++++++++----
4 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/include/asm-generic/hugetlb.h b/include/asm-generic/hugetlb.h
index 8e1e6244a89d..548212eccbd6 100644
--- a/include/asm-generic/hugetlb.h
+++ b/include/asm-generic/hugetlb.h
@@ -27,6 +27,11 @@ static inline pte_t huge_pte_mkdirty(pte_t pte)
return pte_mkdirty(pte);
}

+static inline pte_t huge_pte_mkuffd_wp(pte_t pte)
+{
+ return pte_mkuffd_wp(pte);
+}
+
static inline pte_t huge_pte_modify(pte_t pte, pgprot_t newprot)
{
return pte_modify(pte, newprot);
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index a7f7d5f328dc..ef8d2b8427b1 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -141,7 +141,8 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, pte_t *dst_pte,
unsigned long dst_addr,
unsigned long src_addr,
enum mcopy_atomic_mode mode,
- struct page **pagep);
+ struct page **pagep,
+ bool wp_copy);
#endif /* CONFIG_USERFAULTFD */
bool hugetlb_reserve_pages(struct inode *inode, long from, long to,
struct vm_area_struct *vma,
@@ -321,7 +322,8 @@ static inline int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
unsigned long dst_addr,
unsigned long src_addr,
enum mcopy_atomic_mode mode,
- struct page **pagep)
+ struct page **pagep,
+ bool wp_copy)
{
BUG();
return 0;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index def2c7ddf3ae..f0e55b341ebd 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4725,7 +4725,8 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
unsigned long dst_addr,
unsigned long src_addr,
enum mcopy_atomic_mode mode,
- struct page **pagep)
+ struct page **pagep,
+ bool wp_copy)
{
bool is_continue = (mode == MCOPY_ATOMIC_CONTINUE);
struct address_space *mapping;
@@ -4822,17 +4823,28 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
hugepage_add_new_anon_rmap(page, dst_vma, dst_addr);
}

- /* For CONTINUE on a non-shared VMA, don't set VM_WRITE for CoW. */
- if (is_continue && !vm_shared)
+ /*
+ * For either: (1) CONTINUE on a non-shared VMA, or (2) UFFDIO_COPY
+ * with wp flag set, don't set pte write bit.
+ */
+ if (wp_copy || (is_continue && !vm_shared))
writable = 0;
else
writable = dst_vma->vm_flags & VM_WRITE;

_dst_pte = make_huge_pte(dst_vma, page, writable);
- if (writable)
- _dst_pte = huge_pte_mkdirty(_dst_pte);
+ /*
+ * Always mark UFFDIO_COPY page dirty; note that this may not be
+ * extremely important for hugetlbfs for now since swapping is not
+ * supported, but we should still be clear in that this page cannot be
+ * thrown away at will, even if write bit not set.
+ */
+ _dst_pte = huge_pte_mkdirty(_dst_pte);
_dst_pte = pte_mkyoung(_dst_pte);

+ if (wp_copy)
+ _dst_pte = huge_pte_mkuffd_wp(_dst_pte);
+
set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);

(void)huge_ptep_set_access_flags(dst_vma, dst_addr, dst_pte, _dst_pte,
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 0963e0d9ed20..78471ae3d25c 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -207,7 +207,8 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
unsigned long dst_start,
unsigned long src_start,
unsigned long len,
- enum mcopy_atomic_mode mode)
+ enum mcopy_atomic_mode mode,
+ bool wp_copy)
{
int vm_alloc_shared = dst_vma->vm_flags & VM_SHARED;
int vm_shared = dst_vma->vm_flags & VM_SHARED;
@@ -304,7 +305,8 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
}

err = hugetlb_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma,
- dst_addr, src_addr, mode, &page);
+ dst_addr, src_addr, mode, &page,
+ wp_copy);

mutex_unlock(&hugetlb_fault_mutex_table[hash]);
i_mmap_unlock_read(mapping);
@@ -406,7 +408,8 @@ extern ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
unsigned long dst_start,
unsigned long src_start,
unsigned long len,
- enum mcopy_atomic_mode mode);
+ enum mcopy_atomic_mode mode,
+ bool wp_copy);
#endif /* CONFIG_HUGETLB_PAGE */

static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
@@ -527,7 +530,8 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
*/
if (is_vm_hugetlb_page(dst_vma))
return __mcopy_atomic_hugetlb(dst_mm, dst_vma, dst_start,
- src_start, len, mcopy_mode);
+ src_start, len, mcopy_mode,
+ wp_copy);

if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
goto out_unlock;
--
2.26.2