FROMLIST: fs: list file types that support speculative faults.

Add a speculative field to the vm_operations_struct, which indicates if
the associated file type supports speculative faults.

Initially this is set for files that implement fault() with filemap_fault().

Signed-off-by: Michel Lespinasse <michel@lespinasse.org>
Link: https://lore.kernel.org/all/20210407014502.24091-30-michel@lespinasse.org/
Bug: 161210518
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: Ic92efdf13283c45e7da7bf703f4f85f8b392ba69

fs/btrfs/file.c

@@ -2315,6 +2315,7 @@ static const struct vm_operations_struct btrfs_file_vm_ops = {
 	.fault		= filemap_fault,
 	.map_pages	= filemap_map_pages,
 	.page_mkwrite	= btrfs_page_mkwrite,
+	.speculative	= true,
 };
 
 static int btrfs_file_mmap(struct file	*filp, struct vm_area_struct *vma)

fs/cifs/file.c

@@ -4211,6 +4211,7 @@ static const struct vm_operations_struct cifs_file_vm_ops = {
 	.fault = filemap_fault,
 	.map_pages = filemap_map_pages,
 	.page_mkwrite = cifs_page_mkwrite,
+	.speculative = true,
 };
 
 int cifs_file_strict_mmap(struct file *file, struct vm_area_struct *vma)

fs/fuse/file.c

@@ -2402,6 +2402,7 @@ static const struct vm_operations_struct fuse_file_vm_ops = {
 	.fault		= filemap_fault,
 	.map_pages	= filemap_map_pages,
 	.page_mkwrite	= fuse_page_mkwrite,
+	.speculative	= true,
 };
 
 static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma)

fs/nfs/file.c

@@ -588,6 +588,7 @@ static const struct vm_operations_struct nfs_file_vm_ops = {
 	.fault = filemap_fault,
 	.map_pages = filemap_map_pages,
 	.page_mkwrite = nfs_vm_page_mkwrite,
+	.speculative = true,
 };
 
 static int nfs_need_check_write(struct file *filp, struct inode *inode,

fs/ubifs/file.c

@@ -1598,6 +1598,7 @@ static const struct vm_operations_struct ubifs_file_vm_ops = {
 	.fault        = filemap_fault,
 	.map_pages = filemap_map_pages,
 	.page_mkwrite = ubifs_vm_page_mkwrite,
+	.speculative = true,
 };
 
 static int ubifs_file_mmap(struct file *file, struct vm_area_struct *vma)

fs/vboxsf/file.c

@@ -163,6 +163,7 @@ static const struct vm_operations_struct vboxsf_file_vm_ops = {
 	.close		= vboxsf_vma_close,
 	.fault		= filemap_fault,
 	.map_pages	= filemap_map_pages,
+	.speculative	= true,
 };
 
 static int vboxsf_file_mmap(struct file *file, struct vm_area_struct *vma)

include/linux/mm.h

@@ -663,6 +663,13 @@ struct vm_operations_struct {
 	 */
 	struct page *(*find_special_page)(struct vm_area_struct *vma,
 					  unsigned long addr);
+	/*
+	 * speculative indicates that the vm_operations support
+	 * speculative page faults. This allows ->fault and ->map_pages
+	 * to be called with FAULT_FLAG_SPECULATIVE set; such calls will
+	 * run within an rcu read locked section and with mmap lock not held.
+	 */
+	bool speculative;
 };
 
 static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)

mm/filemap.c

@@ -3425,6 +3425,7 @@ const struct vm_operations_struct generic_file_vm_ops = {
 	.fault		= filemap_fault,
 	.map_pages	= filemap_map_pages,
 	.page_mkwrite	= filemap_page_mkwrite,
+	.speculative	= true,
 };
 
 /* This is used for a general mmap of a disk file */