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 <[email protected]> > To: Richard Henderson <[email protected]> > To: Ivan Kokshaysky <[email protected]> > To: Matt Turner <[email protected]> > To: Vineet Gupta <[email protected]> > To: Russell King <[email protected]> > To: Guo Ren <[email protected]> > To: Huacai Chen <[email protected]> > To: WANG Xuerui <[email protected]> > To: Thomas Bogendoerfer <[email protected]> > To: James E.J. Bottomley <[email protected]> > To: Helge Deller <[email protected]> > To: Michael Ellerman <[email protected]> > To: Nicholas Piggin <[email protected]> > To: Christophe Leroy <[email protected]> > To: Naveen N Rao <[email protected]> > To: Alexander Gordeev <[email protected]> > To: Gerald Schaefer <[email protected]> > To: Heiko Carstens <[email protected]> > To: Vasily Gorbik <[email protected]> > To: Christian Borntraeger <[email protected]> > To: Sven Schnelle <[email protected]> > To: Yoshinori Sato <[email protected]> > To: Rich Felker <[email protected]> > To: John Paul Adrian Glaubitz <[email protected]> > To: David S. Miller <[email protected]> > To: Andreas Larsson <[email protected]> > To: Thomas Gleixner <[email protected]> > To: Ingo Molnar <[email protected]> > To: Borislav Petkov <[email protected]> > To: Dave Hansen <[email protected]> > To: [email protected] > To: H. Peter Anvin <[email protected]> > To: Andy Lutomirski <[email protected]> > To: Peter Zijlstra <[email protected]> > To: Muchun Song <[email protected]> > To: Andrew Morton <[email protected]> > To: Liam R. Howlett <[email protected]> > To: Vlastimil Babka <[email protected]> > To: Lorenzo Stoakes <[email protected]> > To: Shuah Khan <[email protected]> > To: Christoph Hellwig <[email protected]> > To: Michal Hocko <[email protected]> > To: "Kirill A. Shutemov" <[email protected]> > To: Chris Torek <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Signed-off-by: Charlie Jenkins <[email protected]> > > 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/[email protected] > > Changes in v3: > - Use a personality flag instead of an mmap flag > - Link to v2: > https://lore.kernel.org/r/[email protected] > > --- > 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
