[PATCH 00/15] mm: expand mmap_prepare functionality and usage

Lorenzo Stoakes (Oracle)
2026-03-12T20:27:53Z

This series expands the mmap_prepare functionality, which is intended to
replace the deprecated f_op->mmap hook which has been the source of bugs
and security issues for some time.

This series starts with some cleanup of existing mmap_prepare logic, then
adds documentation for the mmap_prepare call to make it easier for
filesystem and driver writers to understand how it works.

It then importantly adds a vm_ops->mapped hook, a key feature that was
missing from mmap_prepare previously - this is invoked when a driver which
specifies mmap_prepare has successfully been mapped but not merged with
another VMA.

Importantly, mmap_prepare is invoked prior to a merge being attempted, so
you cannot manipulate state such as reference counts as if it were a new
mapping.

The vm_ops->mapped hook allows a driver to perform tasks required at this
stage, and provides symmetry against subsequent vm_ops->open,close calls.

The series uses this to correct the afs implementation which wrongly
manipulated reference count at mmap_prepare time.

It then adds an mmap_prepare equivalent of vm_iomap_memory() -
mmap_action_simple_ioremap(), then uses this to update a number of drivers.

It then splits out the mmap_prepare compatibility layer (which allows for
invocation of mmap_prepare hooks in an mmap() hook) in such a way as to
allow for more incremental implementation of mmap_prepare hooks.

It then uses this to extend mmap_prepare usage in drivers.

Finally it adds an mmap_prepare equivalent of vm_map_pages(), which lays
the foundation for future work which will extend mmap_prepare to DMA
coherent mappings.

Lorenzo Stoakes (Oracle) (15):
mm: various small mmap_prepare cleanups
mm: add documentation for the mmap_prepare file operation callback
mm: document vm_operations_struct->open the same as close()
mm: add vm_ops->mapped hook
fs: afs: correctly drop reference count on mapping failure
mm: add mmap_action_simple_ioremap()
misc: open-dice: replace deprecated mmap hook with mmap_prepare
hpet: replace deprecated mmap hook with mmap_prepare
mtdchar: replace deprecated mmap hook with mmap_prepare, clean up
stm: replace deprecated mmap hook with mmap_prepare
staging: vme_user: replace deprecated mmap hook with mmap_prepare
mm: allow handling of stacked mmap_prepare hooks in more drivers
drivers: hv: vmbus: replace deprecated mmap hook with mmap_prepare
uio: replace deprecated mmap hook with mmap_prepare in uio_info
mm: add mmap_action_map_kernel_pages[_full]()

Documentation/driver-api/vme.rst | 2 +-
Documentation/filesystems/mmap_prepare.rst | 141 ++++++++++++++
drivers/char/hpet.c | 12 +-
drivers/hv/hyperv_vmbus.h | 4 +-
drivers/hv/vmbus_drv.c | 27 ++-
drivers/hwtracing/stm/core.c | 31 ++-
drivers/misc/open-dice.c | 19 +-
drivers/mtd/mtdchar.c | 21 +-
drivers/staging/vme_user/vme.c | 20 +-
drivers/staging/vme_user/vme.h | 2 +-
drivers/staging/vme_user/vme_user.c | 51 +++--
drivers/target/target_core_user.c | 26 ++-
drivers/uio/uio.c | 10 +-
drivers/uio/uio_hv_generic.c | 11 +-
fs/afs/file.c | 20 +-
include/linux/fs.h | 14 +-
include/linux/hyperv.h | 4 +-
include/linux/mm.h | 158 +++++++++++++--
include/linux/mm_types.h | 17 +-
include/linux/uio_driver.h | 4 +-
mm/internal.h | 41 ++--
mm/memory.c | 174 ++++++++++++-----
mm/util.c | 213 +++++++++++++++------
mm/vma.c | 56 ++++--
mm/vma.h | 2 +-
tools/testing/vma/include/dup.h | 143 ++++++++++----
tools/testing/vma/include/stubs.h | 9 +-
27 files changed, 933 insertions(+), 299 deletions(-)
create mode 100644 Documentation/filesystems/mmap_prepare.rst

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2.53.0