[PATCH RFC v3 0/2] mm: Introduce ADDR_LIMIT_47BIT personality flag

Charlie Jenkins
2024-09-05T21:16:13Z

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 48-bit address space,
unless the hint address uses more than 47 bits (the 48th bit is reserved
for the kernel address space).

The riscv architecture needs a way to similarly restrict the virtual
address space. On the riscv port of OpenJDK an error is thrown if
attempted to run on the 57-bit address space, called sv57 [1]. golang
has a comment that sv57 support is not complete, but there are some
workarounds to get it to mostly work [2].

These applications work on x86 because x86 does an implicit 47-bit
restriction of mmap() address that contain a hint address that is less
than 48 bits.

Instead of implicitly restricting the address space on riscv (or any
current/future architecture), provide a flag to the personality syscall
that can be used to ensure an application works in any arbitrary VA
space. A similar feature has already been implemented by the personality
syscall in ADDR_LIMIT_32BIT.

This flag will also allow seemless compatibility between all
architectures, so applications like Go and OpenJDK that use bits in a
virtual address can request the exact number of bits they need in a
generic way. The flag can be checked inside of vm_unmapped_area() so
that this flag does not have to be handled individually by each
architecture.

Link:
https://github.com/openjdk/jdk/blob/f080b4bb8a75284db1b6037f8c00ef3b1ef1add1/src/hotspot/cpu/riscv/vm_version_riscv.cpp#L79
[1]
Link:
https://github.com/golang/go/blob/9e8ea567c838574a0f14538c0bbbd83c3215aa55/src/runtime/tagptr_64bit.go#L47
[2]

To: Arnd Bergmann <arnd@arndb.de>
To: Richard Henderson <richard.henderson@linaro.org>
To: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
To: Matt Turner <mattst88@gmail.com>
To: Vineet Gupta <vgupta@kernel.org>
To: Russell King <linux@armlinux.org.uk>
To: Guo Ren <guoren@kernel.org>
To: Huacai Chen <chenhuacai@kernel.org>
To: WANG Xuerui <kernel@xen0n.name>
To: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
To: James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
To: Helge Deller <deller@gmx.de>
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: 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: 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: Andy Lutomirski <luto@kernel.org>
To: Peter Zijlstra <peterz@infradead.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: Shuah Khan <shuah@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
To: Michal Hocko <mhocko@suse.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Chris Torek <chris.torek@gmail.com>
Cc: linux-arch@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-alpha@vger.kernel.org
Cc: linux-snps-arc@lists.infradead.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-csky@vger.kernel.org
Cc: loongarch@lists.linux.dev
Cc: linux-mips@vger.kernel.org
Cc: linux-parisc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: sparclinux@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-kselftest@vger.kernel.org
Cc: linux-abi-devel@lists.sourceforge.net
Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>

Changes in v2:
- Added much greater detail to cover letter
- Removed all code that touched architecture specific code and was able
to factor this out into all generic functions, except for flags that
needed to be added to vm_unmapped_area_info
- Made this an RFC since I have only tested it on riscv and x86
- Link to v1: https://lore.kernel.org/r/20240827-patches-below_hint_mmap-v1-0-46ff2eb9022d@rivosinc.com

Changes in v3:
- Use a personality flag instead of an mmap flag
- Link to v2: https://lore.kernel.org/r/20240829-patches-below_hint_mmap-v2-0-638a28d9eae0@rivosinc.com

---
Charlie Jenkins (2):
mm: Add personality flag to limit address to 47 bits
selftests/mm: Create ADDR_LIMIT_47BIT test

include/uapi/linux/personality.h | 1 +
mm/mmap.c | 3 ++
tools/testing/selftests/mm/.gitignore | 1 +
tools/testing/selftests/mm/Makefile | 1 +
tools/testing/selftests/mm/map_47bit_personality.c | 34 ++++++++++++++++++++++
5 files changed, 40 insertions(+)
---
base-commit: 5be63fc19fcaa4c236b307420483578a56986a37
change-id: 20240827-patches-below_hint_mmap-b13d79ae1c55
--
- Charlie