mm/nommu: factor out check for NOMMU shared mappings into is_nommu_shared_mapping()
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@redhat.com
Link: https://lkml.kernel.org/r/20230102160856.500584-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Nicolas Pitre <nico@fluxnic.net>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
diff --git a/mm/nommu.c b/mm/nommu.c
index 5b83938..1671ebb 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -958,9 +958,10 @@ static int do_mmap_private(struct vm_area_struct *vma,
*/
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 */
@@ -1600,7 +1601,7 @@ static unsigned long do_mremap(unsigned long addr,
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)
