[PATCH v4 0/7] Make core VMA operations internal and testable

From: Lorenzo Stoakes
Date: Mon Jul 29 2024 - 07:51:49 EST

There are a number of "core" VMA manipulation functions implemented in
mm/mmap.c, notably those concerning VMA merging, splitting, modifying,
expanding and shrinking, which logically don't belong there.

More importantly this functionality represents an internal implementation
detail of memory management and should not be exposed outside of mm/
itself.

This patch series isolates core VMA manipulation functionality into its own
file, mm/vma.c, and provides an API to the rest of the mm code in mm/vma.h.

Importantly, it also carefully implements mm/vma_internal.h, which
specifies which headers need to be imported by vma.c, leading to the very
useful property that vma.c depends only on mm/vma.h and mm/vma_internal.h.

This means we can then re-implement vma_internal.h in userland, adding
shims for kernel mechanisms as required, allowing us to unit test internal
VMA functionality.

This testing is useful as opposed to an e.g. kunit implementation as this
way we can avoid all external kernel side-effects while testing, run tests
VERY quickly, and iterate on and debug problems quickly.

Excitingly this opens the door to, in the future, recreating precise
problems observed in production in userland and very quickly debugging
problems that might otherwise be very difficult to reproduce.

This patch series takes advantage of existing shim logic and full userland
maple tree support contained in tools/testing/radix-tree/ and
tools/include/linux/, separating out shared components of the radix tree
implementation to provide this testing.

Kernel functionality is stubbed and shimmed as needed in tools/testing/vma/
which contains a fully functional userland vma_internal.h file and which
imports mm/vma.c and mm/vma.h to be directly tested from userland.

A simple, skeleton testing implementation is provided in
tools/testing/vma/vma.c as a proof-of-concept, asserting that simple VMA
merge, modify (testing split), expand and shrink functionality work
correctly.

v4:
* Rebased on v6.11-rc1.
* Fixed radix-tree Makefile to build all targets.
* Cleaned up trivial issues with test make logic.
* Applied the 2 small fix patches from v3 - fix double header include and
remove invalid asm/ header includes.

v3:
* Rebase on Linus's tree.
* Remove unnecessary use of extern keyword.
https://lore.kernel.org/all/cover.1721648367.git.lorenzo.stoakes@xxxxxxxxxx/

v2:
* NOMMU fixup in mm/vma.h.
* Fixup minor incorrect header edits and remove accidentally included empty
test file, and incorrect license header.
* Remove generated/autoconf.h file from tools/testing/vma/ and create
directory if doesn't already exist.
* Have vma binary return an error code if any tests fail.
https://lore.kernel.org/all/cover.1720121068.git.lorenzo.stoakes@xxxxxxxxxx/

v1:
* Fix test_simple_modify() to specify correct prev.
* Improve vma test Makefile so it picks up dependency changes correctly.
* Rename relocate_vma() to relocate_vma_down().
* Remove shift_arg_pages() and invoked relocate_vma_down() directly from
setup_arg_pages().
* MAINTAINERS fixups.
https://lore.kernel.org/all/cover.1720006125.git.lorenzo.stoakes@xxxxxxxxxx/

RFC v2:
* Reword commit messages.
* Replace vma_expand() / vma_shrink() wrappers with relocate_vma().
* Make move_page_tables() internal too.
* Have internal.h import vma.h.
* Use header guards to more cleanly implement userland testing code.
* Rename main.c to vma.c.
* Update mm/vma_internal.h to have fewer superfluous comments.
* Rework testing logic so we count test failures, and output test results.
* Correct some SPDX license prefixes.
* Make VM_xxx_ON() debug asserts forward to xxx_ON() macros.
* Update VMA tests to correctly free memory, and re-enable ASAN leak
detection.
https://lore.kernel.org/all/cover.1719584707.git.lstoakes@xxxxxxxxx/

RFC v1:
https://lore.kernel.org/all/cover.1719481836.git.lstoakes@xxxxxxxxx/


Lorenzo Stoakes (7):
userfaultfd: move core VMA manipulation logic to mm/userfaultfd.c
mm: move vma_modify() and helpers to internal header
mm: move vma_shrink(), vma_expand() to internal header
mm: move internal core VMA manipulation functions to own file
MAINTAINERS: Add entry for new VMA files
tools: separate out shared radix-tree components
tools: add skeleton code for userland testing of VMA logic

MAINTAINERS | 14 +
fs/exec.c | 81 +-
fs/userfaultfd.c | 160 +-
include/linux/mm.h | 112 +-
include/linux/userfaultfd_k.h | 19 +
mm/Makefile | 2 +-
mm/internal.h | 167 +-
mm/mmap.c | 2069 ++---------------
mm/mmu_notifier.c | 2 +
mm/userfaultfd.c | 168 ++
mm/vma.c | 1766 ++++++++++++++
mm/vma.h | 364 +++
mm/vma_internal.h | 50 +
tools/testing/radix-tree/.gitignore | 1 +
tools/testing/radix-tree/Makefile | 72 +-
tools/testing/radix-tree/xarray.c | 10 +-
.../generated => shared}/autoconf.h | 0
tools/testing/{radix-tree => shared}/linux.c | 0
.../{radix-tree => shared}/linux/bug.h | 0
.../{radix-tree => shared}/linux/cpu.h | 0
.../{radix-tree => shared}/linux/idr.h | 0
.../{radix-tree => shared}/linux/init.h | 0
.../{radix-tree => shared}/linux/kconfig.h | 0
.../{radix-tree => shared}/linux/kernel.h | 0
.../{radix-tree => shared}/linux/kmemleak.h | 0
.../{radix-tree => shared}/linux/local_lock.h | 0
.../{radix-tree => shared}/linux/lockdep.h | 0
.../{radix-tree => shared}/linux/maple_tree.h | 0
.../{radix-tree => shared}/linux/percpu.h | 0
.../{radix-tree => shared}/linux/preempt.h | 0
.../{radix-tree => shared}/linux/radix-tree.h | 0
.../{radix-tree => shared}/linux/rcupdate.h | 0
.../{radix-tree => shared}/linux/xarray.h | 0
tools/testing/shared/maple-shared.h | 9 +
tools/testing/shared/maple-shim.c | 7 +
tools/testing/shared/shared.h | 33 +
tools/testing/shared/shared.mk | 72 +
.../trace/events/maple_tree.h | 0
tools/testing/shared/xarray-shared.c | 5 +
tools/testing/shared/xarray-shared.h | 4 +
tools/testing/vma/.gitignore | 7 +
tools/testing/vma/Makefile | 16 +
tools/testing/vma/linux/atomic.h | 12 +
tools/testing/vma/linux/mmzone.h | 38 +
tools/testing/vma/vma.c | 207 ++
tools/testing/vma/vma_internal.h | 882 +++++++
46 files changed, 3907 insertions(+), 2442 deletions(-)
create mode 100644 mm/vma.c
create mode 100644 mm/vma.h
create mode 100644 mm/vma_internal.h
rename tools/testing/{radix-tree/generated => shared}/autoconf.h (100%)
rename tools/testing/{radix-tree => shared}/linux.c (100%)
rename tools/testing/{radix-tree => shared}/linux/bug.h (100%)
rename tools/testing/{radix-tree => shared}/linux/cpu.h (100%)
rename tools/testing/{radix-tree => shared}/linux/idr.h (100%)
rename tools/testing/{radix-tree => shared}/linux/init.h (100%)
rename tools/testing/{radix-tree => shared}/linux/kconfig.h (100%)
rename tools/testing/{radix-tree => shared}/linux/kernel.h (100%)
rename tools/testing/{radix-tree => shared}/linux/kmemleak.h (100%)
rename tools/testing/{radix-tree => shared}/linux/local_lock.h (100%)
rename tools/testing/{radix-tree => shared}/linux/lockdep.h (100%)
rename tools/testing/{radix-tree => shared}/linux/maple_tree.h (100%)
rename tools/testing/{radix-tree => shared}/linux/percpu.h (100%)
rename tools/testing/{radix-tree => shared}/linux/preempt.h (100%)
rename tools/testing/{radix-tree => shared}/linux/radix-tree.h (100%)
rename tools/testing/{radix-tree => shared}/linux/rcupdate.h (100%)
rename tools/testing/{radix-tree => shared}/linux/xarray.h (100%)
create mode 100644 tools/testing/shared/maple-shared.h
create mode 100644 tools/testing/shared/maple-shim.c
create mode 100644 tools/testing/shared/shared.h
create mode 100644 tools/testing/shared/shared.mk
rename tools/testing/{radix-tree => shared}/trace/events/maple_tree.h (100%)
create mode 100644 tools/testing/shared/xarray-shared.c
create mode 100644 tools/testing/shared/xarray-shared.h
create mode 100644 tools/testing/vma/.gitignore
create mode 100644 tools/testing/vma/Makefile
create mode 100644 tools/testing/vma/linux/atomic.h
create mode 100644 tools/testing/vma/linux/mmzone.h
create mode 100644 tools/testing/vma/vma.c
create mode 100644 tools/testing/vma/vma_internal.h

--
2.45.2