linux-kernel - Re: [PATCH v4 0/2] riscv: errata: thead: use riscv_nonstd_cache_ops for CMO

Open Source and information security mailing list archives

Message-ID: <ZUvBzDytyoz/Hqvk@xhacker>
Date:   Thu, 9 Nov 2023 01:13:48 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>
Cc:     Guo Ren <guoren@...nel.org>, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/2] riscv: errata: thead: use riscv_nonstd_cache_ops
 for CMO

On Thu, Oct 12, 2023 at 10:37:44PM +0800, Jisheng Zhang wrote:
> Previously, we use alternative mechanism to dynamically patch
> the CMO operations for THEAD C906/C910 during boot for performance
> reason. But as pointed out by Arnd, "there is already a significant
> cost in accessing the invalidated cache lines afterwards, which is
> likely going to be much higher than the cost of an indirect branch".
> And indeed, there's no performance difference with GMAC and EMMC per
> my test on Sipeed Lichee Pi 4A board.
> 
> Use riscv_nonstd_cache_ops for THEAD C906/C910 CMO to simplify
> the alternative code, and to acchieve Arnd's goal -- "I think
> moving the THEAD ops at the same level as all nonstandard operations
> makes sense, but I'd still leave CMO as an explicit fast path that
> avoids the indirect branch. This seems like the right thing to do both
> for readability and for platforms on which the indirect branch has a
> noticeable overhead."
> 
> To make bisect easy, I use two patches here: patch1 does the conversion
> which just mimics current CMO behavior via. riscv_nonstd_cache_ops, I
> assume no functionalities changes. patch2 uses T-HEAD PA based CMO
> instructions so that we don't need to covert PA to VA.

Hi Palmer,

I know you are busy ;) Just want to know is there any chance for this
series to be merged for v6.7?

Thanks
> 
> Hi Guo,
> 
> I didn't use wback_inv for wback as you suggested during v1 reviewing,
> this can be left as future optimizations.
> 
> Thanks
> 
> since v3:
>   - collect Reviewed-by tag
> 
> since v2:
>   - collect Reviewed-by tag (but missed them in fact)
>   - fix typo
> 
> since v1:
>   - collect Tested-by tag
>   - add patch2 to use T-HEAD PA based CMO instructions.
> 
> Jisheng Zhang (2):
>   riscv: errata: thead: use riscv_nonstd_cache_ops for CMO
>   riscv: errata: thead: use pa based instructions for CMO
> 
>  arch/riscv/Kconfig.errata            |  1 +
>  arch/riscv/errata/thead/errata.c     | 69 +++++++++++++++++++++++++++-
>  arch/riscv/include/asm/errata_list.h | 50 +++-----------------
>  3 files changed, 74 insertions(+), 46 deletions(-)
> 
> -- 
> 2.40.1
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives