[PATCH v3 0/4] riscv: tlb flush improvements

From: Alexandre Ghiti
Date: Tue Aug 01 2023 - 04:54:13 EST

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)

Any other idea welcome.

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

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 flush_tlb()
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/tlb.h | 8 ++-
arch/riscv/include/asm/tlbflush.h | 12 ++--
arch/riscv/mm/tlbflush.c | 98 ++++++++++++++++++++++++++-----
3 files changed, 99 insertions(+), 19 deletions(-)