All of lore.kernel.org
 help / color / mirror / Atom feed
From: Paul Walmsley <pjw@kernel.org>
To: Vivian Wang <wangruikang@iscas.ac.cn>
Cc: "Clément Léger" <cleger@rivosinc.com>,
	"Paul Walmsley" <pjw@kernel.org>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Alexandre Ghiti" <alex@ghiti.fr>,
	"Andrew Jones" <ajones@ventanamicro.com>,
	"Conor Dooley" <conor@kernel.org>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org, "Songsong Zhang" <U2FsdGVkX1@gmail.com>
Subject: Re: [PATCH v2] riscv: misaligned: Make enabling delegation depend on NONPORTABLE
Date: Wed, 13 May 2026 22:30:50 -0600 (MDT)	[thread overview]
Message-ID: <ed77660c-84d2-ce2f-3b21-01a3309ed997@kernel.org> (raw)
In-Reply-To: <20260401-riscv-misaligned-dont-delegate-v2-1-5014a288c097@iscas.ac.cn>

On Wed, 1 Apr 2026, Vivian Wang wrote:

> The unaligned access emulation code in Linux has various deficiencies.
> For example, it doesn't emulate vector instructions [1] [2], and doesn't
> emulate KVM guest accesses. Therefore, requesting misaligned exception
> delegation with SBI FWFT actually regresses vector instructions' and KVM
> guests' behavior.
> 
> Until Linux can handle it properly, guard these sbi_fwft_set() calls
> behind RISCV_SBI_FWFT_DELEGATE_MISALIGNED, which in turn depends on
> NONPORTABLE. Those who are sure that this wouldn't be a problem can
> enable this option, perhaps getting better performance.
> 
> The rest of the existing code proceeds as before, except as if
> SBI_FWFT_MISALIGNED_EXC_DELEG is not available, to handle any remaining
> address misaligned exceptions on a best-effort basis. The KVM SBI FWFT
> implementation is also not touched, but it is disabled if the firmware
> emulates unaligned accesses.
> 
> Cc: stable@vger.kernel.org
> Fixes: cf5a8abc6560 ("riscv: misaligned: request misaligned exception from SBI")
> Reported-by: Songsong Zhang <U2FsdGVkX1@gmail.com> # KVM
> Link: https://lore.kernel.org/linux-riscv/38ce44c1-08cf-4e3f-8ade-20da224f529c@iscas.ac.cn/ [1]
> Link: https://lore.kernel.org/linux-riscv/b3cfcdac-0337-4db0-a611-258f2868855f@iscas.ac.cn/ [2]
> Signed-off-by: Vivian Wang <wangruikang@iscas.ac.cn>

Thanks, queued for v7.1-rc.


- Paul

WARNING: multiple messages have this Message-ID (diff)
From: Paul Walmsley <pjw@kernel.org>
To: Vivian Wang <wangruikang@iscas.ac.cn>
Cc: "Clément Léger" <cleger@rivosinc.com>,
	"Paul Walmsley" <pjw@kernel.org>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Alexandre Ghiti" <alex@ghiti.fr>,
	"Andrew Jones" <ajones@ventanamicro.com>,
	"Conor Dooley" <conor@kernel.org>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org, "Songsong Zhang" <U2FsdGVkX1@gmail.com>
Subject: Re: [PATCH v2] riscv: misaligned: Make enabling delegation depend on NONPORTABLE
Date: Wed, 13 May 2026 22:30:50 -0600 (MDT)	[thread overview]
Message-ID: <ed77660c-84d2-ce2f-3b21-01a3309ed997@kernel.org> (raw)
In-Reply-To: <20260401-riscv-misaligned-dont-delegate-v2-1-5014a288c097@iscas.ac.cn>

On Wed, 1 Apr 2026, Vivian Wang wrote:

> The unaligned access emulation code in Linux has various deficiencies.
> For example, it doesn't emulate vector instructions [1] [2], and doesn't
> emulate KVM guest accesses. Therefore, requesting misaligned exception
> delegation with SBI FWFT actually regresses vector instructions' and KVM
> guests' behavior.
> 
> Until Linux can handle it properly, guard these sbi_fwft_set() calls
> behind RISCV_SBI_FWFT_DELEGATE_MISALIGNED, which in turn depends on
> NONPORTABLE. Those who are sure that this wouldn't be a problem can
> enable this option, perhaps getting better performance.
> 
> The rest of the existing code proceeds as before, except as if
> SBI_FWFT_MISALIGNED_EXC_DELEG is not available, to handle any remaining
> address misaligned exceptions on a best-effort basis. The KVM SBI FWFT
> implementation is also not touched, but it is disabled if the firmware
> emulates unaligned accesses.
> 
> Cc: stable@vger.kernel.org
> Fixes: cf5a8abc6560 ("riscv: misaligned: request misaligned exception from SBI")
> Reported-by: Songsong Zhang <U2FsdGVkX1@gmail.com> # KVM
> Link: https://lore.kernel.org/linux-riscv/38ce44c1-08cf-4e3f-8ade-20da224f529c@iscas.ac.cn/ [1]
> Link: https://lore.kernel.org/linux-riscv/b3cfcdac-0337-4db0-a611-258f2868855f@iscas.ac.cn/ [2]
> Signed-off-by: Vivian Wang <wangruikang@iscas.ac.cn>

Thanks, queued for v7.1-rc.


- Paul

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

  parent reply	other threads:[~2026-05-14  4:30 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-04-01  1:53 [PATCH v2] riscv: misaligned: Make enabling delegation depend on NONPORTABLE Vivian Wang
2026-04-01  1:53 ` Vivian Wang
2026-04-01  8:57 ` Conor Dooley
2026-04-01  8:57   ` Conor Dooley
2026-05-14  4:30 ` Paul Walmsley [this message]
2026-05-14  4:30   ` Paul Walmsley

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=ed77660c-84d2-ce2f-3b21-01a3309ed997@kernel.org \
    --to=pjw@kernel.org \
    --cc=U2FsdGVkX1@gmail.com \
    --cc=ajones@ventanamicro.com \
    --cc=alex@ghiti.fr \
    --cc=cleger@rivosinc.com \
    --cc=conor@kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-riscv@lists.infradead.org \
    --cc=palmer@dabbelt.com \
    --cc=stable@vger.kernel.org \
    --cc=wangruikang@iscas.ac.cn \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.