[PATCH v6 0/4] riscv: tlb flush improvements

[Alexandre Ghiti]

This series optimizes the tlb flushes on riscv which used to simply
flush the whole tlb whatever the size of the range to flush or the size
of the stride.

Patch 3 introduces a threshold that is microarchitecture specific and
will very likely be modified by vendors, not sure though which mechanism
we'll use to do that (dt? alternatives? vendor initialization code?).

Next steps would be to implement:
- svinval extension as Mayuresh did here [1]
- BATCHED_UNMAP_TLB_FLUSH (I'll wait for arm64 patchset to land)
- MMU_GATHER_RCU_TABLE_FREE
- MMU_GATHER_MERGE_VMAS

Any other idea welcome.

[1] https://lore.kernel.org/linux-riscv/20230623123849.1425805-1-mchitale@ventanamicro.com/

Changes in v6:
- Remove ifdef SVNAPOT, as suggested by Samuel
- Fix usage of u16 which could overflow, as noted by Samuel
- Use cpu_online_mask, as suggested by Samuel
- Move static_branch_unlikely(&use_asid_allocator) test, as suggested by Samuel
- Add TB/RB from Prabhakar and Samuel, thanks guys!

Changes in v5:
- Fix commit message s/flush_tlb/tlb_flush thanks to Samuel
- Simplify NAPOT mapping stride size handling, as suggested by Samuel
- Add TB from Prabhakar
- Add RB from Samuel
- Remove TB/RB from patch 2 as it changed enough

Changes in v4:
- Correctly handle the stride size for a NAPOT hugepage, thanks to Aaron Durbin!
- Fix flush_tlb_kernel_range() which passed a wrong argument to __flush_tlb_range()
- Factorize code to handle asid/no asid flushes
- Fix kernel flush bug where I used to pass 0 instead of x0, big thanks to Samuel for finding that!

Changes in v3:
- Add RB from Andrew, thanks!
- Unwrap a few lines, as suggested by Andrew
- Introduce defines for -1 constants used in tlbflush.c, as suggested by Andrew and Conor
- Use huge_page_size() directly instead of using the shift, as suggested by Andrew
- Remove misleading comments as suggested by Conor

Changes in v2:
- Make static tlb_flush_all_threshold, we'll figure out later how to
  override this value on a vendor basis, as suggested by Conor and Palmer
- Fix nommu build, as reported by Conor

Alexandre Ghiti (4):
  riscv: Improve tlb_flush()
  riscv: Improve flush_tlb_range() for hugetlb pages
  riscv: Make __flush_tlb_range() loop over pte instead of flushing the
    whole tlb
  riscv: Improve flush_tlb_kernel_range()

 arch/riscv/include/asm/sbi.h      |   3 -
 arch/riscv/include/asm/tlb.h      |   8 +-
 arch/riscv/include/asm/tlbflush.h |  15 ++-
 arch/riscv/kernel/sbi.c           |  32 ++----
 arch/riscv/mm/tlbflush.c          | 181 +++++++++++++++++++-----------
 5 files changed, 144 insertions(+), 95 deletions(-)

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2.39.2