From a2138fee6ce78339899919ea4cd7c4472dcbdb01 Mon Sep 17 00:00:00 2001
From: Michel Lespinasse <michel@lespinasse.org>
Date: Thu, 29 Apr 2021 10:28:25 -0700
Subject: [PATCH] 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    | 1 +
 fs/cifs/file.c     | 1 +
 fs/fuse/file.c     | 1 +
 fs/nfs/file.c      | 1 +
 fs/ubifs/file.c    | 1 +
 fs/vboxsf/file.c   | 1 +
 include/linux/mm.h | 7 +++++++
 mm/filemap.c       | 1 +
 8 files changed, 14 insertions(+)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index e44742b55746..853334910a5f 100644
--- a/fs/btrfs/file.c
+++ b/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)
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 82bbaf8e92b7..baeecc877880 100644
--- a/fs/cifs/file.c
+++ b/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)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 70b5421d7133..fdbad561df38 100644
--- a/fs/fuse/file.c
+++ b/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)
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index aa353fd58240..d8dc3620706d 100644
--- a/fs/nfs/file.c
+++ b/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,
diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 5cfa28cd00cd..c994c8062f60 100644
--- a/fs/ubifs/file.c
+++ b/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)
diff --git a/fs/vboxsf/file.c b/fs/vboxsf/file.c
index 864c2fad23be..2bdfdfc826a5 100644
--- a/fs/vboxsf/file.c
+++ b/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)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index e699e407aadc..db9916f6caae 100644
--- a/include/linux/mm.h
+++ b/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)
diff --git a/mm/filemap.c b/mm/filemap.c
index 27f52e186199..02fb6c79fe90 100644
--- a/mm/filemap.c
+++ b/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 */