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

[John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>]

Hi Charlie,

On Thu, 2024-09-05 at 14:15 -0700, Charlie Jenkins wrote:
> 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

Wow, this issue has been plaguing SPARC users for years already as the architecture
uses a 52-bit virtual address space and Javascript engines such as the one in Firefox
or Webkit have been crashing ever since.

I should definitely give this series a try and see if that fixes Javascript crashes
on SPARC.

Thanks a lot for addressing this nasty long-standing problem!

Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913