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

[Samuel Holland <samuel@sholland.org>]

On 8/1/23 03:53, Alexandre Ghiti wrote:
> 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?).

Certainly we would want to set the threshold to zero on SiFive platforms
affected by CIP-1200, since they cannot use address-based sfence.vma at
all. At least this case could be handled in the existing errata patch
function. I don't know about other platforms.

Regards,
Samuel

> 
> 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 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(-)
>