The patch titled
Subject: mm/nommu: factor out check for NOMMU shared mappings into is_nommu_shared_mapping()
has been added to the -mm mm-unstable branch. Its filename is
mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/nommu: factor out check for NOMMU shared mappings into is_nommu_shared_mapping()
Date: Mon, 2 Jan 2023 17:08:54 +0100
Patch series "mm/nommu: don't use VM_MAYSHARE for MAP_PRIVATE mappings".
Trying to reduce the confusion around VM_SHARED and VM_MAYSHARE first
requires !CONFIG_MMU to stop using VM_MAYSHARE for MAP_PRIVATE mappings.
CONFIG_MMU only sets VM_MAYSHARE for MAP_SHARED mappings.
This paves the way for further VM_MAYSHARE and VM_SHARED cleanups: for
example, renaming VM_MAYSHARED to VM_MAP_SHARED to make it cleaner what is
actually means.
Let's first get the weird case out of the way and not use VM_MAYSHARE in
MAP_PRIVATE mappings, using a new VM_MAYOVERLAY flag instead.
This patch (of 3):
We want to stop using VM_MAYSHARE in private mappings to pave the way for
clarifying the semantics of VM_MAYSHARE vs. VM_SHARED and reduce the
confusion. While CONFIG_MMU uses VM_MAYSHARE to represent MAP_SHARED,
!CONFIG_MMU also sets VM_MAYSHARE for selected R/O private file mappings
that are an effective overlay of a file mapping.
Let's factor out all relevant VM_MAYSHARE checks in !CONFIG_MMU code into
is_nommu_shared_mapping() first.
Note that whenever VM_SHARED is set, VM_MAYSHARE must be set as well
(unless there is a serious BUG). So there is not need to test for
VM_SHARED manually.
No functional change intended.
Link: https://lkml.kernel.org/r/20230102160856.500584-1-david@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20230102160856.500584-2-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Nicolas Pitre <nico@xxxxxxxxxxx>
Cc: Pavel Begunkov <asml.silence@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/char/mem.c | 2 +-
fs/cramfs/inode.c | 2 +-
fs/proc/task_nommu.c | 2 +-
fs/ramfs/file-nommu.c | 2 +-
fs/romfs/mmap-nommu.c | 2 +-
include/linux/mm.h | 15 +++++++++++++++
io_uring/io_uring.c | 2 +-
mm/nommu.c | 11 ++++++-----
8 files changed, 27 insertions(+), 11 deletions(-)
--- a/drivers/char/mem.c~mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping
+++ a/drivers/char/mem.c
@@ -343,7 +343,7 @@ static unsigned zero_mmap_capabilities(s
/* can't do an in-place private mapping if there's no MMU */
static inline int private_mapping_ok(struct vm_area_struct *vma)
{
- return vma->vm_flags & VM_MAYSHARE;
+ return is_nommu_shared_mapping(vma->vm_flags);
}
#else
--- a/fs/cramfs/inode.c~mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping
+++ a/fs/cramfs/inode.c
@@ -437,7 +437,7 @@ bailout:
static int cramfs_physmem_mmap(struct file *file, struct vm_area_struct *vma)
{
- return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -ENOSYS;
+ return is_nommu_shared_mapping(vma->vm_flags) ? 0 : -ENOSYS;
}
static unsigned long cramfs_physmem_get_unmapped_area(struct file *file,
--- a/fs/proc/task_nommu.c~mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping
+++ a/fs/proc/task_nommu.c
@@ -38,7 +38,7 @@ void task_mem(struct seq_file *m, struct
}
if (atomic_read(&mm->mm_count) > 1 ||
- vma->vm_flags & VM_MAYSHARE) {
+ is_nommu_shared_mapping(vma->vm_flags)) {
sbytes += size;
} else {
bytes += size;
--- a/fs/ramfs/file-nommu.c~mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping
+++ a/fs/ramfs/file-nommu.c
@@ -264,7 +264,7 @@ out:
*/
static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
{
- if (!(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)))
+ if (!is_nommu_shared_mapping(vma->vm_flags))
return -ENOSYS;
file_accessed(file);
--- a/fs/romfs/mmap-nommu.c~mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping
+++ a/fs/romfs/mmap-nommu.c
@@ -63,7 +63,7 @@ static unsigned long romfs_get_unmapped_
*/
static int romfs_mmap(struct file *file, struct vm_area_struct *vma)
{
- return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -ENOSYS;
+ return is_nommu_shared_mapping(vma->vm_flags) ? 0 : -ENOSYS;
}
static unsigned romfs_mmap_capabilities(struct file *file)
--- a/include/linux/mm.h~mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping
+++ a/include/linux/mm.h
@@ -1385,6 +1385,21 @@ static inline bool is_cow_mapping(vm_fla
return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
}
+#ifndef CONFIG_MMU
+static inline bool is_nommu_shared_mapping(vm_flags_t flags)
+{
+ /*
+ * NOMMU shared mappings are ordinary MAP_SHARED mappings and selected
+ * R/O MAP_PRIVATE file mappings that are an effective R/O overlay of
+ * a file mapping. R/O MAP_PRIVATE mappings might still modify
+ * underlying memory if ptrace is active, so this is only possible if
+ * ptrace does not apply. Note that there is no mprotect() to upgrade
+ * write permissions later.
+ */
+ return flags & VM_MAYSHARE;
+}
+#endif
+
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
#define SECTION_IN_PAGE_FLAGS
#endif
--- a/io_uring/io_uring.c~mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping
+++ a/io_uring/io_uring.c
@@ -3194,7 +3194,7 @@ static __cold int io_uring_mmap(struct f
static int io_uring_mmap(struct file *file, struct vm_area_struct *vma)
{
- return vma->vm_flags & (VM_SHARED | VM_MAYSHARE) ? 0 : -EINVAL;
+ return is_nommu_shared_mapping(vma->vm_flags) ? 0 : -EINVAL;
}
static unsigned int io_uring_nommu_mmap_capabilities(struct file *file)
--- a/mm/nommu.c~mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping
+++ a/mm/nommu.c
@@ -958,9 +958,10 @@ static int do_mmap_private(struct vm_are
*/
if (capabilities & NOMMU_MAP_DIRECT) {
ret = call_mmap(vma->vm_file, vma);
+ /* shouldn't return success if we're not sharing */
+ if (WARN_ON_ONCE(!is_nommu_shared_mapping(vma->vm_flags)))
+ ret = -ENOSYS;
if (ret == 0) {
- /* shouldn't return success if we're not sharing */
- BUG_ON(!(vma->vm_flags & VM_MAYSHARE));
vma->vm_region->vm_top = vma->vm_region->vm_end;
return 0;
}
@@ -1106,7 +1107,7 @@ unsigned long do_mmap(struct file *file,
* these cases, sharing is handled in the driver or filesystem rather
* than here
*/
- if (vm_flags & VM_MAYSHARE) {
+ if (is_nommu_shared_mapping(vm_flags)) {
struct vm_region *pregion;
unsigned long pglen, rpglen, pgend, rpgend, start;
@@ -1116,7 +1117,7 @@ unsigned long do_mmap(struct file *file,
for (rb = rb_first(&nommu_region_tree); rb; rb = rb_next(rb)) {
pregion = rb_entry(rb, struct vm_region, vm_rb);
- if (!(pregion->vm_flags & VM_MAYSHARE))
+ if (!is_nommu_shared_mapping(pregion->vm_flags))
continue;
/* search for overlapping mappings on the same file */
@@ -1597,7 +1598,7 @@ static unsigned long do_mremap(unsigned
if (vma->vm_end != vma->vm_start + old_len)
return (unsigned long) -EFAULT;
- if (vma->vm_flags & VM_MAYSHARE)
+ if (is_nommu_shared_mapping(vma->vm_flags))
return (unsigned long) -EPERM;
if (new_len > vma->vm_region->vm_end - vma->vm_region->vm_start)
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-hugetlb-fix-pte-marker-handling-in-hugetlb_change_protection.patch
mm-hugetlb-fix-uffd-wp-handling-for-migration-entries-in-hugetlb_change_protection.patch
mm-userfaultfd-enable-writenotify-while-userfaultfd-wp-is-enabled-for-a-vma.patch
mm-userfaultfd-rely-on-vma-vm_page_prot-in-uffd_wp_range.patch
mm-userfaultfd-rely-on-vma-vm_page_prot-in-uffd_wp_range-fix.patch
mm-mprotect-drop-pgprot_t-parameter-from-change_protection.patch
mm-mprotect-drop-pgprot_t-parameter-from-change_protection-fix.patch
selftests-vm-cow-add-cow-tests-for-collapsing-of-pte-mapped-anon-thp.patch
mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping.patch
mm-nommu-dont-use-vm_mayshare-for-map_private-mappings.patch
drivers-misc-open-dice-dont-touch-vm_mayshare.patch
