[PATCH 00/16] mm: Introduce MAP_BELOW_HINT

Charlie Jenkins
2024-08-28T05:49:26Z

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