Re: [RFC PATCH v2 00/21] riscv: Introduce 64K base page

[Zi Yan]

On 5 Dec 2024, at 5:37, Xu Lu wrote:

> This patch series attempts to break through the limitation of MMU and
> supports larger base page on RISC-V, which only supports 4K page size
> now. The key idea is to always manage and allocate memory at a
> granularity of 64K and use SVNAPOT to accelerate address translation.
> This is the second version and the detailed introduction can be found
> in [1].
>
> Changes from v1:
> - Rebase on v6.12.
>
> - Adjust the page table entry shift to reduce page table memory usage.
>     For example, in SV39, the traditional va behaves as:
>
>     ----------------------------------------------
>     | pgd index | pmd index | pte index | offset |
>     ----------------------------------------------
>     | 38     30 | 29     21 | 20     12 | 11   0 |
>     ----------------------------------------------
>
>     When we choose 64K as basic software page, va now behaves as:
>
>     ----------------------------------------------
>     | pgd index | pmd index | pte index | offset |
>     ----------------------------------------------
>     | 38     34 | 33     25 | 24     16 | 15   0 |
>     ----------------------------------------------
>
> - Fix some bugs in v1.
>
> Thanks in advance for comments.
>
> [1] https://lwn.net/Articles/952722/

This looks very interesting. Can you cc me and linux-mm@xxxxxxxxx
in the future? Thanks.

Have you thought about doing it for ARM64 4KB as well? ARM64’s contig PTE
should have similar effect of RISC-V’s SVNAPOT, right?

>
> Xu Lu (21):
>   riscv: mm: Distinguish hardware base page and software base page
>   riscv: mm: Configure satp with hw page pfn
>   riscv: mm: Reimplement page table entry structures
>   riscv: mm: Reimplement page table entry constructor function
>   riscv: mm: Reimplement conversion functions between page table entry
>   riscv: mm: Avoid pte constructor during pte conversion
>   riscv: mm: Reimplement page table entry get function
>   riscv: mm: Reimplement page table entry atomic get function
>   riscv: mm: Replace READ_ONCE with atomic pte get function
>   riscv: mm: Reimplement PTE A/D bit check function
>   riscv: mm: Reimplement mk_huge_pte function
>   riscv: mm: Reimplement tlb flush function
>   riscv: mm: Adjust PGDIR/P4D/PUD/PMD_SHIFT
>   riscv: mm: Only apply svnapot region bigger than software page
>   riscv: mm: Adjust FIX_BTMAPS_SLOTS for variable PAGE_SIZE
>   riscv: mm: Adjust FIX_FDT_SIZE for variable PMD_SIZE
>   riscv: mm: Apply Svnapot for base page mapping if possible
>   riscv: Kconfig: Introduce 64K page size
>   riscv: Kconfig: Adjust mmap rnd bits for 64K Page
>   riscv: mm: Adjust address space layout and init page table for 64K
>     Page
>   riscv: mm: Update EXEC_PAGESIZE for 64K Page
>
>  arch/riscv/Kconfig                    |  34 +-
>  arch/riscv/include/asm/fixmap.h       |   3 +-
>  arch/riscv/include/asm/hugetlb.h      |   5 +
>  arch/riscv/include/asm/page.h         |  56 ++-
>  arch/riscv/include/asm/pgtable-32.h   |  12 +-
>  arch/riscv/include/asm/pgtable-64.h   | 128 ++++--
>  arch/riscv/include/asm/pgtable-bits.h |   3 +-
>  arch/riscv/include/asm/pgtable.h      | 564 +++++++++++++++++++++++---
>  arch/riscv/include/asm/tlbflush.h     |  26 +-
>  arch/riscv/include/uapi/asm/param.h   |  24 ++
>  arch/riscv/kernel/head.S              |   4 +-
>  arch/riscv/kernel/hibernate.c         |  21 +-
>  arch/riscv/mm/context.c               |   7 +-
>  arch/riscv/mm/fault.c                 |  15 +-
>  arch/riscv/mm/hugetlbpage.c           |  30 +-
>  arch/riscv/mm/init.c                  |  45 +-
>  arch/riscv/mm/kasan_init.c            |   7 +-
>  arch/riscv/mm/pgtable.c               | 111 ++++-
>  arch/riscv/mm/tlbflush.c              |  31 +-
>  arch/s390/include/asm/hugetlb.h       |   2 +-
>  include/asm-generic/hugetlb.h         |   5 +-
>  include/linux/pgtable.h               |  21 +
>  kernel/events/core.c                  |   6 +-
>  mm/debug_vm_pgtable.c                 |   6 +-
>  mm/gup.c                              |  10 +-
>  mm/hmm.c                              |   2 +-
>  mm/hugetlb.c                          |   4 +-
>  mm/mapping_dirty_helpers.c            |   2 +-
>  mm/memory.c                           |   4 +-
>  mm/mprotect.c                         |   2 +-
>  mm/ptdump.c                           |   8 +-
>  mm/sparse-vmemmap.c                   |   2 +-
>  mm/vmscan.c                           |   2 +-
>  33 files changed, 1029 insertions(+), 173 deletions(-)
>  create mode 100644 arch/riscv/include/uapi/asm/param.h
>
> -- 
> 2.20.1


Best Regards,
Yan, Zi