[PATCH RFC 20/30] hugetlb/userfaultfd: Handle UFFDIO_WRITEPROTECT

[Peter Xu <peterx@redhat.com>]

This starts from passing cp_flags into hugetlb_change_protection() so hugetlb
will be able to handle MM_CP_UFFD_WP[_RESOLVE] requests.

huge_pte_clear_uffd_wp() is introduced to handle the case where the
UFFDIO_WRITEPROTECT is requested upon migrating huge page entries.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 include/asm-generic/hugetlb.h |  5 +++++
 include/linux/hugetlb.h       |  6 ++++--
 mm/hugetlb.c                  | 13 ++++++++++++-
 mm/mprotect.c                 |  3 ++-
 mm/userfaultfd.c              |  8 ++++++++
 5 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/include/asm-generic/hugetlb.h b/include/asm-generic/hugetlb.h
index 548212eccbd6..181cdc3297e7 100644
--- a/include/asm-generic/hugetlb.h
+++ b/include/asm-generic/hugetlb.h
@@ -32,6 +32,11 @@ static inline pte_t huge_pte_mkuffd_wp(pte_t pte)
 	return pte_mkuffd_wp(pte);
 }
 
+static inline pte_t huge_pte_clear_uffd_wp(pte_t pte)
+{
+	return pte_clear_uffd_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 bd061f7eedcb..fe1dde0afbaf 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -185,7 +185,8 @@ struct page *follow_huge_pgd(struct mm_struct *mm, unsigned long address,
 int pmd_huge(pmd_t pmd);
 int pud_huge(pud_t pud);
 unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
-		unsigned long address, unsigned long end, pgprot_t newprot);
+		unsigned long address, unsigned long end, pgprot_t newprot,
+		unsigned long cp_flags);
 
 bool is_hugetlb_entry_migration(pte_t pte);
 
@@ -343,7 +344,8 @@ static inline void move_hugetlb_state(struct page *oldpage,
 
 static inline unsigned long hugetlb_change_protection(
 			struct vm_area_struct *vma, unsigned long address,
-			unsigned long end, pgprot_t newprot)
+			unsigned long end, pgprot_t newprot,
+			unsigned long cp_flags)
 {
 	return 0;
 }
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 563b8f70537f..18b236bac6cd 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4938,7 +4938,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 #endif
 
 unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
-		unsigned long address, unsigned long end, pgprot_t newprot)
+		unsigned long address, unsigned long end,
+		pgprot_t newprot, unsigned long cp_flags)
 {
 	struct mm_struct *mm = vma->vm_mm;
 	unsigned long start = address;
@@ -4948,6 +4949,8 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
 	unsigned long pages = 0;
 	bool shared_pmd = false;
 	struct mmu_notifier_range range;
+	bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
+	bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;
 
 	/*
 	 * In the case of shared PMDs, the area to flush could be beyond
@@ -4988,6 +4991,10 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
 
 				make_migration_entry_read(&entry);
 				newpte = swp_entry_to_pte(entry);
+				if (uffd_wp)
+					newpte = pte_swp_mkuffd_wp(newpte);
+				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));
 				pages++;
@@ -5001,6 +5008,10 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
 			old_pte = huge_ptep_modify_prot_start(vma, address, ptep);
 			pte = pte_mkhuge(huge_pte_modify(old_pte, newprot));
 			pte = arch_make_huge_pte(pte, vma, NULL, 0);
+			if (uffd_wp)
+				pte = huge_pte_mkuffd_wp(huge_pte_wrprotect(pte));
+			else if (uffd_wp_resolve)
+				pte = huge_pte_clear_uffd_wp(pte);
 			huge_ptep_modify_prot_commit(vma, address, ptep, old_pte, pte);
 			pages++;
 		}
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 055871322007..fce87ac99117 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -416,7 +416,8 @@ unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
 	BUG_ON((cp_flags & MM_CP_UFFD_WP_ALL) == MM_CP_UFFD_WP_ALL);
 
 	if (is_vm_hugetlb_page(vma))
-		pages = hugetlb_change_protection(vma, start, end, newprot);
+		pages = hugetlb_change_protection(vma, start, end, newprot,
+						  cp_flags);
 	else
 		pages = change_protection_range(vma, start, end, newprot,
 						cp_flags);
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index b00e5e6b8b8b..480d91b783d4 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -644,6 +644,7 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
 			unsigned long len, bool enable_wp, bool *mmap_changing)
 {
 	struct vm_area_struct *dst_vma;
+	unsigned long page_mask;
 	pgprot_t newprot;
 	int err;
 
@@ -680,6 +681,13 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
 	if (!vma_is_anonymous(dst_vma))
 		goto out_unlock;
 
+	if (is_vm_hugetlb_page(dst_vma)) {
+		err = -EINVAL;
+		page_mask = vma_kernel_pagesize(dst_vma) - 1;
+		if ((start & page_mask) || (len & page_mask))
+			goto out_unlock;
+	}
+
 	if (enable_wp)
 		newprot = vm_get_page_prot(dst_vma->vm_flags & ~(VM_WRITE));
 	else
-- 
2.26.2