[PATCH RFC 19/30] hugetlb/userfaultfd: Take care of UFFDIO_COPY_MODE_WP

[Peter Xu]

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@xxxxxxxxxx>
---
 include/asm-generic/hugetlb.h |  5 +++++
 include/linux/hugetlb.h       |  6 ++++--
 mm/hugetlb.c                  |  9 +++++++--
 mm/userfaultfd.c              | 12 ++++++++----
 4 files changed, 24 insertions(+), 8 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 ebca2ef02212..bd061f7eedcb 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -138,7 +138,8 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, pte_t *dst_pte,
 				struct vm_area_struct *dst_vma,
 				unsigned long dst_addr,
 				unsigned long src_addr,
-				struct page **pagep);
+				struct page **pagep,
+				bool wp_copy);
 int hugetlb_reserve_pages(struct inode *inode, long from, long to,
 						struct vm_area_struct *vma,
 						vm_flags_t vm_flags);
@@ -313,7 +314,8 @@ static inline int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 						struct vm_area_struct *dst_vma,
 						unsigned long dst_addr,
 						unsigned long src_addr,
-						struct page **pagep)
+						struct page **pagep,
+						bool wp_copy)
 {
 	BUG();
 	return 0;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index dcbbba53bd10..563b8f70537f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4624,7 +4624,8 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 			    struct vm_area_struct *dst_vma,
 			    unsigned long dst_addr,
 			    unsigned long src_addr,
-			    struct page **pagep)
+			    struct page **pagep,
+			    bool wp_copy)
 {
 	struct address_space *mapping;
 	pgoff_t idx;
@@ -4717,8 +4718,12 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 	}
 
 	_dst_pte = make_huge_pte(dst_vma, page, dst_vma->vm_flags & VM_WRITE);
-	if (dst_vma->vm_flags & VM_WRITE)
+	if (dst_vma->vm_flags & VM_WRITE) {
 		_dst_pte = huge_pte_mkdirty(_dst_pte);
+		if (wp_copy)
+			_dst_pte = huge_pte_mkuffd_wp(
+			    huge_pte_wrprotect(_dst_pte));
+	}
 	_dst_pte = pte_mkyoung(_dst_pte);
 
 	set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 6d4b3b7c7f9f..b00e5e6b8b8b 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,
-					      bool zeropage)
+					      bool zeropage,
+					      bool wp_copy)
 {
 	int vm_alloc_shared = dst_vma->vm_flags & VM_SHARED;
 	int vm_shared = dst_vma->vm_flags & VM_SHARED;
@@ -306,7 +307,8 @@ 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, &page);
+					       dst_addr, src_addr, &page,
+					       wp_copy);
 
 		mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 		i_mmap_unlock_read(mapping);
@@ -408,7 +410,8 @@ extern ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
 				      unsigned long dst_start,
 				      unsigned long src_start,
 				      unsigned long len,
-				      bool zeropage);
+				      bool zeropage,
+				      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, zeropage);
+					       src_start, len, zeropage,
+					       wp_copy);
 
 	if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
 		goto out_unlock;
-- 
2.26.2