[PATCH 00/16] mm: Introduce MAP_BELOW_HINT

[Charlie Jenkins]

Some applications rely on placing data in free bits addresses allocated
by mmap. Various architectures (eg. x86, arm64, powerpc) restrict the
address returned by mmap to be less than the maximum address space,
unless the hint address is greater than this value.

On arm64 this barrier is at 52 bits and on x86 it is at 56 bits. This
flag allows applications a way to specify exactly how many bits they
want to be left unused by mmap. This eliminates the need for
applications to know the page table hierarchy of the system to be able
to reason which addresses mmap will be allowed to return.

---
riscv made this feature of mmap returning addresses less than the hint
address the default behavior. This was in contrast to the implementation
of x86/arm64 that have a single boundary at the 5-level page table
region. However this restriction proved too great -- the reduced
address space when using a hint address was too small.

A patch for riscv [1] reverts the behavior that broke userspace. This
series serves to make this feature available to all architectures.

I have only tested on riscv and x86. There is a tremendous amount of
duplicated code in mmap so the implementations across architectures I
believe should be mostly consistent. I added this feature to all
architectures that implement either
arch_get_mmap_end()/arch_get_mmap_base() or
arch_get_unmapped_area_topdown()/arch_get_unmapped_area(). I also added
it to the default behavior for arch_get_mmap_end()/arch_get_mmap_base().

Link: https://lore.kernel.org/lkml/20240826-riscv_mmap-v1-2-cd8962afe47f@rivosinc.com/T/ [1]

To: Arnd Bergmann <arnd at arndb.de>
To: Paul Walmsley <paul.walmsley at sifive.com>
To: Palmer Dabbelt <palmer at dabbelt.com>
To: Albert Ou <aou at eecs.berkeley.edu>
To: Catalin Marinas <catalin.marinas at arm.com>
To: Will Deacon <will at kernel.org>
To: Michael Ellerman <mpe at ellerman.id.au>
To: Nicholas Piggin <npiggin at gmail.com>
To: Christophe Leroy <christophe.leroy at csgroup.eu>
To: Naveen N Rao <naveen at kernel.org>
To: Muchun Song <muchun.song at linux.dev>
To: Andrew Morton <akpm at linux-foundation.org>
To: Liam R. Howlett <Liam.Howlett at oracle.com>
To: Vlastimil Babka <vbabka at suse.cz>
To: Lorenzo Stoakes <lorenzo.stoakes at oracle.com>
To: Thomas Gleixner <tglx at linutronix.de>
To: Ingo Molnar <mingo at redhat.com>
To: Borislav Petkov <bp at alien8.de>
To: Dave Hansen <dave.hansen at linux.intel.com>
To: x86 at kernel.org
To: H. Peter Anvin <hpa at zytor.com>
To: Huacai Chen <chenhuacai at kernel.org>
To: WANG Xuerui <kernel at xen0n.name>
To: Russell King <linux at armlinux.org.uk>
To: Thomas Bogendoerfer <tsbogend at alpha.franken.de>
To: James E.J. Bottomley <James.Bottomley at HansenPartnership.com>
To: Helge Deller <deller at gmx.de>
To: Alexander Gordeev <agordeev at linux.ibm.com>
To: Gerald Schaefer <gerald.schaefer at linux.ibm.com>
To: Heiko Carstens <hca at linux.ibm.com>
To: Vasily Gorbik <gor at linux.ibm.com>
To: Christian Borntraeger <borntraeger at linux.ibm.com>
To: Sven Schnelle <svens at linux.ibm.com>
To: Yoshinori Sato <ysato at users.sourceforge.jp>
To: Rich Felker <dalias at libc.org>
To: John Paul Adrian Glaubitz <glaubitz at physik.fu-berlin.de>
To: David S. Miller <davem at davemloft.net>
To: Andreas Larsson <andreas at gaisler.com>
To: Shuah Khan <shuah at kernel.org>
To: Alexandre Ghiti <alexghiti at rivosinc.com>
Cc: linux-arch at vger.kernel.org
Cc: linux-kernel at vger.kernel.org
Cc: Palmer Dabbelt <palmer at rivosinc.com>
Cc: linux-riscv at lists.infradead.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: linuxppc-dev at lists.ozlabs.org
Cc: linux-mm at kvack.org
Cc: loongarch at lists.linux.dev
Cc: linux-mips at vger.kernel.org
Cc: linux-parisc at vger.kernel.org
Cc: linux-s390 at vger.kernel.org
Cc: linux-sh at vger.kernel.org
Cc: sparclinux at vger.kernel.org
Cc: linux-kselftest at vger.kernel.org
Signed-off-by: Charlie Jenkins <charlie at rivosinc.com>

---
Charlie Jenkins (16):
      mm: Add MAP_BELOW_HINT
      riscv: mm: Do not restrict mmap address based on hint
      mm: Add flag and len param to arch_get_mmap_base()
      mm: Add generic MAP_BELOW_HINT
      riscv: mm: Support MAP_BELOW_HINT
      arm64: mm: Support MAP_BELOW_HINT
      powerpc: mm: Support MAP_BELOW_HINT
      x86: mm: Support MAP_BELOW_HINT
      loongarch: mm: Support MAP_BELOW_HINT
      arm: mm: Support MAP_BELOW_HINT
      mips: mm: Support MAP_BELOW_HINT
      parisc: mm: Support MAP_BELOW_HINT
      s390: mm: Support MAP_BELOW_HINT
      sh: mm: Support MAP_BELOW_HINT
      sparc: mm: Support MAP_BELOW_HINT
      selftests/mm: Create MAP_BELOW_HINT test

 arch/arm/mm/mmap.c                           | 10 ++++++++
 arch/arm64/include/asm/processor.h           | 34 ++++++++++++++++++++++----
 arch/loongarch/mm/mmap.c                     | 11 +++++++++
 arch/mips/mm/mmap.c                          |  9 +++++++
 arch/parisc/include/uapi/asm/mman.h          |  1 +
 arch/parisc/kernel/sys_parisc.c              |  9 +++++++
 arch/powerpc/include/asm/task_size_64.h      | 36 +++++++++++++++++++++++-----
 arch/riscv/include/asm/processor.h           | 32 -------------------------
 arch/s390/mm/mmap.c                          | 10 ++++++++
 arch/sh/mm/mmap.c                            | 10 ++++++++
 arch/sparc/kernel/sys_sparc_64.c             |  8 +++++++
 arch/x86/kernel/sys_x86_64.c                 | 25 ++++++++++++++++---
 fs/hugetlbfs/inode.c                         |  2 +-
 include/linux/sched/mm.h                     | 34 ++++++++++++++++++++++++--
 include/uapi/asm-generic/mman-common.h       |  1 +
 mm/mmap.c                                    |  2 +-
 tools/arch/parisc/include/uapi/asm/mman.h    |  1 +
 tools/include/uapi/asm-generic/mman-common.h |  1 +
 tools/testing/selftests/mm/Makefile          |  1 +
 tools/testing/selftests/mm/map_below_hint.c  | 29 ++++++++++++++++++++++
 20 files changed, 216 insertions(+), 50 deletions(-)
---
base-commit: 5be63fc19fcaa4c236b307420483578a56986a37
change-id: 20240827-patches-below_hint_mmap-b13d79ae1c55
-- 
- Charlie