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

Thu Sep 5 23:19:17 PDT 2024

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

-- 
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