[PATCH v4 02/12] mm/secretmem: set AS_NO_DIRECT_MAP instead of special-casing

[Patrick Roy <roypat@amazon.co.uk>]

Make secretmem set AS_NO_DIRECT_MAP on its struct address_space, to drop
all the vma_is_secretmem()/secretmem_mapping() checks that are based on
checking explicitly for the secretmem ops structures.

This drops a optimization in gup_fast_folio_allowed() where
secretmem_mapping() was only called if CONFIG_SECRETMEM=y. secretmem is
enabled by default since commit b758fe6df50d ("mm/secretmem: make it on
by default"), so the secretmem check did not actually end up elided in
most cases anymore anyway.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>
---
 include/linux/secretmem.h | 18 ------------------
 lib/buildid.c             |  2 +-
 mm/gup.c                  | 14 +-------------
 mm/mlock.c                |  3 +--
 mm/secretmem.c            |  6 +-----
 5 files changed, 4 insertions(+), 39 deletions(-)

diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h
index e918f96881f5..0ae1fb057b3d 100644
--- a/include/linux/secretmem.h
+++ b/include/linux/secretmem.h
@@ -4,28 +4,10 @@
 
 #ifdef CONFIG_SECRETMEM
 
-extern const struct address_space_operations secretmem_aops;
-
-static inline bool secretmem_mapping(struct address_space *mapping)
-{
-	return mapping->a_ops == &secretmem_aops;
-}
-
-bool vma_is_secretmem(struct vm_area_struct *vma);
 bool secretmem_active(void);
 
 #else
 
-static inline bool vma_is_secretmem(struct vm_area_struct *vma)
-{
-	return false;
-}
-
-static inline bool secretmem_mapping(struct address_space *mapping)
-{
-	return false;
-}
-
 static inline bool secretmem_active(void)
 {
 	return false;
diff --git a/lib/buildid.c b/lib/buildid.c
index 80b5d805067f..33f173a607ad 100644
--- a/lib/buildid.c
+++ b/lib/buildid.c
@@ -66,7 +66,7 @@ static int freader_get_folio(struct freader *r, loff_t file_off)
 	freader_put_folio(r);
 
 	/* reject secretmem folios created with memfd_secret() or guest_memfd() */
-	if (secretmem_mapping(r->file->f_mapping) || mapping_no_direct_map(r->file->f_mapping))
+	if (mapping_no_direct_map(r->file->f_mapping))
 		return -EFAULT;
 
 	r->folio = filemap_get_folio(r->file->f_mapping, file_off >> PAGE_SHIFT);
diff --git a/mm/gup.c b/mm/gup.c
index 7ddaf93c5b6a..b1483a876740 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1283,7 +1283,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
 	if ((gup_flags & FOLL_LONGTERM) && vma_is_fsdax(vma))
 		return -EOPNOTSUPP;
 
-	if (vma_is_secretmem(vma) || vma_is_no_direct_map(vma))
+	if (vma_is_no_direct_map(vma))
 		return -EFAULT;
 
 	if (write) {
@@ -2786,7 +2786,6 @@ static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags)
 {
 	bool reject_file_backed = false;
 	struct address_space *mapping;
-	bool check_secretmem = false;
 	unsigned long mapping_flags;
 
 	/*
@@ -2798,14 +2797,6 @@ static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags)
 		reject_file_backed = true;
 
 	/* We hold a folio reference, so we can safely access folio fields. */
-
-	/* secretmem folios are always order-0 folios. */
-	if (IS_ENABLED(CONFIG_SECRETMEM) && !folio_test_large(folio))
-		check_secretmem = true;
-
-	if (!reject_file_backed && !check_secretmem)
-		return true;
-
 	if (WARN_ON_ONCE(folio_test_slab(folio)))
 		return false;
 
@@ -2847,9 +2838,6 @@ static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags)
 	 * At this point, we know the mapping is non-null and points to an
 	 * address_space object.
 	 */
-	if (check_secretmem && secretmem_mapping(mapping))
-		return false;
-
 	if (mapping_no_direct_map(mapping))
 		return false;
 
diff --git a/mm/mlock.c b/mm/mlock.c
index 07a351491d9d..a43f308be70d 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -474,8 +474,7 @@ static int mlock_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
 
 	if (newflags == oldflags || (oldflags & VM_SPECIAL) ||
 	    is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm) ||
-	    vma_is_dax(vma) || vma_is_secretmem(vma) || vma_is_no_direct_map(vma) ||
-	    (oldflags & VM_DROPPABLE))
+	    vma_is_dax(vma) || vma_is_no_direct_map(vma) || (oldflags & VM_DROPPABLE))
 		/* don't set VM_LOCKED or VM_LOCKONFAULT and don't count */
 		goto out;
 
diff --git a/mm/secretmem.c b/mm/secretmem.c
index 1b0a214ee558..ea4c04d469b1 100644
--- a/mm/secretmem.c
+++ b/mm/secretmem.c
@@ -136,11 +136,6 @@ static int secretmem_mmap(struct file *file, struct vm_area_struct *vma)
 	return 0;
 }
 
-bool vma_is_secretmem(struct vm_area_struct *vma)
-{
-	return vma->vm_ops == &secretmem_vm_ops;
-}
-
 static const struct file_operations secretmem_fops = {
 	.release	= secretmem_release,
 	.mmap		= secretmem_mmap,
@@ -214,6 +209,7 @@ static struct file *secretmem_file_create(unsigned long flags)
 
 	mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
 	mapping_set_unevictable(inode->i_mapping);
+	mapping_set_no_direct_map(inode->i_mapping);
 
 	inode->i_op = &secretmem_iops;
 	inode->i_mapping->a_ops = &secretmem_aops;
-- 
2.48.1