From patchwork Thu Jan 26 17:06:06 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Guo Ren X-Patchwork-Id: 13117510 X-Patchwork-Delegate: palmer@dabbelt.com 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A9D76C05027 for ; Thu, 26 Jan 2023 17:06:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=RiP9pw4wQ9QDnBmgChWSnYo06yoGOrbISzAPyxkFrSE=; b=HPRIcJMVOhk/4D fvVq2kj7F6JQMnJIVAcmh3KfC3ZOOIyXpMPMYjPew17l21y1f2Dx0eO669/zpt3PjajtE+JnmmMk8 n3D+BCtUv1FGfzHwfFsNICNS+o1fNtV4EPDLqxkGW4jQxy8iaBn24FFBTQfJJtdtp2JPYt/VwfUBn Q98b3d06KRECx1E4kvyLREHEsaXQ6nClVFqsuQkSSbiEZ9a7407GHzgd1A9QcmVEgETPkfZIrrM5F OzwCrB0LEprmA71dUPfBQdEkjiVn96E00sXyGd1nD7kv37VwFTkB4GjSX2dJL5BOEQFUUHNfQj2qt wm1n00h+1p88nWziF8Ag==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pL5hj-00Bxik-F6; Thu, 26 Jan 2023 17:06:27 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1pL5hf-00Bxgi-L3 for linux-riscv@lists.infradead.org; Thu, 26 Jan 2023 17:06:25 +0000 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 dfw.source.kernel.org (Postfix) with ESMTPS id D484E618F9; Thu, 26 Jan 2023 17:06:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7439AC4339B; Thu, 26 Jan 2023 17:06:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1674752782; bh=ZvStsc5ZtEWBoYSz9j8G0L0vCieAFt37Hxf2WaPKWWw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rb/s6IV3YcxZ4VRJQvCzKHhmseUDBTzSjrE4vMAt2T4RfuOHyH99josgXNwDAZjk4 1n5ppRrKyBdEeLEItArSfRfL6vt0zUqPslv/sjyaNQ3aZErHap+aFy6ZdotoNNvoat QwlhZeArvCbJIUdm73XaXSsSQhDQb3MRgN6kcBHAtHRPvIyGr1c2DnKfQaO80IVr+L j/OiOfCE8Ot4T9ULk2AvtHmiLQIFvtCiUuBV5Hg1G/V0GKIucx7skHdI7+9cnVwuuy ECWwGY51kbg8gm6e1YjyOi5bALvymqIfMByitwME+oq9LKdcrCw4ONNLkt69NeB62n qWp/MSASdtLdw== From: guoren@kernel.org To: guoren@kernel.org, palmer@dabbelt.com, paul.walmsley@sifive.com, mhiramat@kernel.org, conor.dooley@microchip.com, penberg@kernel.org, mark.rutland@arm.com, jrtc27@jrtc27.com, andy.chiu@sifive.com, zong.li@sifive.com Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Greentime Hu Subject: [PATCH -next V3 1/2] riscv: jump_label: Fixup unaligned arch_static_branch function Date: Thu, 26 Jan 2023 12:06:06 -0500 Message-Id: <20230126170607.1489141-2-guoren@kernel.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20230126170607.1489141-1-guoren@kernel.org> References: <20230126170607.1489141-1-guoren@kernel.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230126_090623_760059_8BFA5BFB X-CRM114-Status: GOOD ( 12.97 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org 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.chiu@sifive.com/ Signed-off-by: Andy Chiu Reviewed-by: Greentime Hu Signed-off-by: Guo Ren Reviewed-by: Björn Töpel --- 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/jump_label.h index 6d58bbb5da46..14a5ea8d8ef0 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 static_key * const key, const 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(struct static_key * const ke const bool branch) { asm_volatile_goto( + " .align 2 \n\t" " .option push \n\t" " .option norelax \n\t" " .option norvc \n\t"