From nobody Thu Sep 18 05:25:06 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 480A3C4332F for ; Sat, 10 Dec 2022 10:09:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229876AbiLJKJv (ORCPT ); Sat, 10 Dec 2022 05:09:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39760 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229851AbiLJKJs (ORCPT ); Sat, 10 Dec 2022 05:09:48 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2E549205D1 for ; Sat, 10 Dec 2022 02:09:47 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id AD0F7B82A53 for ; Sat, 10 Dec 2022 10:09:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D155FC433F1; Sat, 10 Dec 2022 10:09:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1670666984; bh=K/60DtPvcZdUEbYVaryyiSYpmJ4q6k25bcoqeghcm6Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=c1gonYSltysNYBdWo1OiUPJAX6nQDNh2VBFXTKSWFvM4XLcSZWi9uw4vkUCo33oHp 5ZwvePgedJRPeibXPM0DauEBUHlHvkKFI1hkkSiaoA4CI8NYysWcKH0GeIzNJzMH0K eehfNuQZYYOYTqErRq0nT6cIuz/rX7499UcL5Pj+t5WNJngiN+R4ZPAvpEpWWaWZla Rpimacv6DCkQwRj/sAXAJi9linKUxlj0lBc90p56MGv2xWgZREJX/UbY3YlYobrN7u 5HG5IF2K70DLgBga9GBvDLq/WLcwif82wrH8b8mCXyuTmFrC8aAKyZvSITaCVzKR8I kZDPj/QyGxU0Q== From: guoren@kernel.org To: palmer@rivosinc.com, conor.Dooley@microchip.com, guoren@kernel.org, andy.chiu@sifive.com, greentime.hu@sifive.com, paul.walmsley@sifive.com, peterz@infradead.org, rostedt@goodmis.org, jrtc27@jrtc27.com Cc: linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Subject: [PATCH -next V2 1/2] riscv: jump_label: Fixup unaligned arch_static_branch function Date: Sat, 10 Dec 2022 05:09:26 -0500 Message-Id: <20221210100927.835145-2-guoren@kernel.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20221210100927.835145-1-guoren@kernel.org> References: <20221210100927.835145-1-guoren@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Andy Chiu Runtime code patching must be done at a naturally aligned address, or we may execute on a partial instruction. We have encountered problems traced back to static jump functions during the test. We switched the tracer randomly for every 1~5 seconds on a dual-core QEMU setup and found the kernel sucking at a static branch where it jumps to itself. The reason is that the static branch was 2-byte but not 4-byte aligned. Then, the kernel would patch the instruction, either J or NOP, with two half-word stores if the machine does not have efficient unaligned accesses. Thus, moments exist where half of the NOP mixes with the other half of the J when transitioning the branch. In our particular case, on a little-endian machine, the upper half of the NOP was mixed with the lower part of the J when enabling the branch, resulting in a jump that jumped to itself. Conversely, it would result in a HINT instruction when disabling the branch, but it might not be observable. ARM64 does not have this problem since all instructions must be 4-byte aligned. Fixes: ebc00dde8a97 ("riscv: Add jump-label implementation") Link: https://lore.kernel.org/linux-riscv/20220913094252.3555240-6-andy.chi= u@sifive.com/ Signed-off-by: Andy Chiu Reviewed-by: Greentime Hu Signed-off-by: Guo Ren --- arch/riscv/include/asm/jump_label.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/riscv/include/asm/jump_label.h b/arch/riscv/include/asm/j= ump_label.h index 38af2ec7b9bf..729991e8f782 100644 --- a/arch/riscv/include/asm/jump_label.h +++ b/arch/riscv/include/asm/jump_label.h @@ -18,6 +18,7 @@ static __always_inline bool arch_static_branch(struct sta= tic_key *key, bool branch) { asm_volatile_goto( + " .align 2 \n\t" " .option push \n\t" " .option norelax \n\t" " .option norvc \n\t" @@ -39,6 +40,7 @@ static __always_inline bool arch_static_branch_jump(struc= t static_key *key, bool branch) { asm_volatile_goto( + " .align 2 \n\t" " .option push \n\t" " .option norelax \n\t" " .option norvc \n\t" --=20 2.36.1