mbox series

[0/2] Make SV39 the default address space

Message ID 20230627222152.177716-1-charlie@rivosinc.com
Headers show
Series Make SV39 the default address space | expand

Message

Charlie Jenkins June 27, 2023, 10:21 p.m. UTC 
Make sv39 the default address space for mmap as some applications
currently depend on this assumption. The RISC-V specification enforces
that bits outside of the virtual address range are not used, so
restricting the size of the default address space as such should be
temporary. A hint address passed to mmap will cause the largest address
space that fits entirely into the hint to be used. If the hint is less
than or equal to 1<<38, a 39-bit address will be used. After an address
space is completely full, the next smallest address space will be used.

Documentation is also added to the RISC-V virtual memory section to explain
these changes.

Charlie Jenkins (2):
  RISC-V: mm: Restrict address space for sv39,sv48,sv57
  RISC-V: mm: Update documentation and include test

 Documentation/riscv/vm-layout.rst             | 20 ++++++++
 arch/riscv/include/asm/elf.h                  |  2 +-
 arch/riscv/include/asm/pgtable.h              | 21 ++++++--
 arch/riscv/include/asm/processor.h            | 41 +++++++++++++---
 tools/testing/selftests/riscv/Makefile        |  2 +-
 tools/testing/selftests/riscv/mm/Makefile     | 22 +++++++++
 .../selftests/riscv/mm/testcases/mmap.c       | 49 +++++++++++++++++++
 7 files changed, 144 insertions(+), 13 deletions(-)
 create mode 100644 tools/testing/selftests/riscv/mm/Makefile
 create mode 100644 tools/testing/selftests/riscv/mm/testcases/mmap.c


base-commit: eef509789cecdce895020682192d32e8bac790e8

Comments

Anup Patel June 28, 2023, 12:34 p.m. UTC | #1 
On Wed, Jun 28, 2023 at 5:09 AM Charlie Jenkins <charlie@rivosinc.com> wrote:
>
> Yes it is small to have a default of 38-bits of userspace. I would be
> interesting in the opinions of other people on whether it would be
> acceptable to have the default be sv48 and require applications that
> prefer fewer bits to specify so with the given mmap hinting.

I think sv48 is a reasonable default instead of sv39. We should fallback
to sv39 only if the underlying host does not support sv48.

Regards,
Anup