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@xxxxxxxxxxxx/T/ [1] To: Arnd Bergmann <arnd@xxxxxxxx> To: Paul Walmsley <paul.walmsley@xxxxxxxxxx> To: Palmer Dabbelt <palmer@xxxxxxxxxxx> To: Albert Ou <aou@xxxxxxxxxxxxxxxxx> To: Catalin Marinas <catalin.marinas@xxxxxxx> To: Will Deacon <will@xxxxxxxxxx> To: Michael Ellerman <mpe@xxxxxxxxxxxxxx> To: Nicholas Piggin <npiggin@xxxxxxxxx> To: Christophe Leroy <christophe.leroy@xxxxxxxxxx> To: Naveen N Rao <naveen@xxxxxxxxxx> To: Muchun Song <muchun.song@xxxxxxxxx> To: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> To: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> To: Vlastimil Babka <vbabka@xxxxxxx> To: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> To: Thomas Gleixner <tglx@xxxxxxxxxxxxx> To: Ingo Molnar <mingo@xxxxxxxxxx> To: Borislav Petkov <bp@xxxxxxxxx> To: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> To: x86@xxxxxxxxxx To: H. Peter Anvin <hpa@xxxxxxxxx> To: Huacai Chen <chenhuacai@xxxxxxxxxx> To: WANG Xuerui <kernel@xxxxxxxxxx> To: Russell King <linux@xxxxxxxxxxxxxxx> To: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx> To: James E.J. Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> To: Helge Deller <deller@xxxxxx> To: Alexander Gordeev <agordeev@xxxxxxxxxxxxx> To: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> To: Heiko Carstens <hca@xxxxxxxxxxxxx> To: Vasily Gorbik <gor@xxxxxxxxxxxxx> To: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx> To: Sven Schnelle <svens@xxxxxxxxxxxxx> To: Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx> To: Rich Felker <dalias@xxxxxxxx> To: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx> To: David S. Miller <davem@xxxxxxxxxxxxx> To: Andreas Larsson <andreas@xxxxxxxxxxx> To: Shuah Khan <shuah@xxxxxxxxxx> To: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> Cc: linux-arch@xxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Cc: Palmer Dabbelt <palmer@xxxxxxxxxxxx> Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx Cc: linuxppc-dev@xxxxxxxxxxxxxxxx Cc: linux-mm@xxxxxxxxx Cc: loongarch@xxxxxxxxxxxxxxx Cc: linux-mips@xxxxxxxxxxxxxxx Cc: linux-parisc@xxxxxxxxxxxxxxx Cc: linux-s390@xxxxxxxxxxxxxxx Cc: linux-sh@xxxxxxxxxxxxxxx Cc: sparclinux@xxxxxxxxxxxxxxx Cc: linux-kselftest@xxxxxxxxxxxxxxx Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx> --- 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
