From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C063DC433E0 for ; Tue, 30 Jun 2020 08:20:56 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8A78420768 for ; Tue, 30 Jun 2020 08:20:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="GuMACHkG"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="Vqbmy70X" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8A78420768 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:MIME-Version:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Message-Id:Date:Subject:To:From:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:In-Reply-To:References:List-Owner; bh=tX8dC1OINqe8PmbhzWJZzMtSpT2mWHbxVcyPcrYkNV4=; b=GuMACHkGeiZ51L64doHfufYr2J wmWkJ8ShSqwbUdgw2N8hEB3k2EJ+qZDcmap67JW9whScz6v3v9KFqOtPIj2gXIM2Qave5ducHz30u 4jMURAjRLdZBw/ek0ve96T2dKdK0/pt6Ekq9uVPs8aV69EXXH05IbgpZb9Y9WUkc1uih4RzNxHr/0 UU96Yg2U7jqOQrlkWO1bClnUQKkh5P/ruvua9C50wtTqV6bhc2SrE6b6UARGiXNbvKsPhnNvARyD/ PGEbjfoOc2aeNvErm+YkzYXGBH0byV5c9uB80raoZ0NqhGc0IMtHeMlUK5ZnhQ32/MX8hI0bTkMXc 7YLplQ3g==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jqBUV-0004r6-Ba; Tue, 30 Jun 2020 08:19:43 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jqBUS-0004qj-FA for linux-arm-kernel@lists.infradead.org; Tue, 30 Jun 2020 08:19:41 +0000 Received: from e123331-lin.nice.arm.com (lfbn-nic-1-188-42.w2-15.abo.wanadoo.fr [2.15.37.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7CD7A20759; Tue, 30 Jun 2020 08:19:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593505179; bh=0OhUD51OpSHtKXpq09RF7LmcoWR4Zqu+oL/wtvw3h6w=; h=From:To:Cc:Subject:Date:From; b=Vqbmy70XCR8WZJ1uevpsE0RrF1GKrabsXhWxIEPqxn23HHPh+ud9ZkcsaUiIcMQNQ /Bd4L8NlPIqe/9NbgTrtQZBMKX5ufRKjgtKaC3fBMg0gm9IUC/2ilw/zZatgV1gTxJ gyjnR6ysKRyuSR7mT9hVTWGepkQGPsxdR9r5x2fk= From: Ard Biesheuvel To: linux-arm-kernel@lists.infradead.org Subject: [PATCH] arm64/alternatives: use subsections for replacement sequences Date: Tue, 30 Jun 2020 10:19:21 +0200 Message-Id: <20200630081921.13443-1-ardb@kernel.org> X-Mailer: git-send-email 2.17.1 X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, anders.roxell@linaro.org, arnd@arndb.de, Suzuki K Poulose , catalin.marinas@arm.com, Dave P Martin , James Morse , Andre Przywara , will@kernel.org, Ard Biesheuvel MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org When building very large kernels, the logic that emits replacement sequences for alternatives fails when relative branches are present in the code that is emitted into the .altinstr_replacement section and patched in at the original site and fixed up. The reason is that the linker will insert veneers if relative branches go out of range, and due to the relative distance of the .altinstr_replacement from the .text section where its branch targets usually live, veneers may be emitted at the end of the .altinstr_replacement section, with the relative branches in the sequence pointed at the veneers instead of the actual target. The alternatives patching logic will attempt to fix up the branch to point to its original target, which will be the veneer in this case, but given that the patch site is likely to be far away as well, it will be out of range and so patching will fail. There are other cases where these veneers are problematic, e.g., when the target of the branch is in .text while the patch site is in .init.text, in which case putting the replacement sequence inside .text may not help either. So let's use subsections to emit the replacement code as closely as possible to the patch site, to ensure that veneers are only likely to be emitted if they are required at the patch site as well, in which case they will be in range for the replacement sequence both before and after it is transported to the patch site. This will prevent alternative sequences in non-init code from being released from memory after boot, but this is tolerable given that the entire section is only 512 KB on an allyesconfig build (which weighs in at 500+ MB for the entire Image). Also, note that modules today carry the replacement sequences in non-init sections as well, and any of those that target init code will be emitted into init sections after this change. This fixes an early crash when booting an allyesconfig kernel on a system where any of the alternatives sequences containing relative branches are activated at boot (e.g., ARM64_HAS_PAN on TX2) Cc: Suzuki K Poulose Cc: James Morse Cc: Andre Przywara Cc: Dave P Martin Signed-off-by: Ard Biesheuvel --- arch/arm64/include/asm/alternative.h | 16 ++++++++-------- arch/arm64/kernel/vmlinux.lds.S | 3 --- 2 files changed, 8 insertions(+), 11 deletions(-) diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h index 5e5dc05d63a0..12f0eb56a1cc 100644 --- a/arch/arm64/include/asm/alternative.h +++ b/arch/arm64/include/asm/alternative.h @@ -73,11 +73,11 @@ static inline void apply_alternatives_module(void *start, size_t length) { } ".pushsection .altinstructions,\"a\"\n" \ ALTINSTR_ENTRY(feature) \ ".popsection\n" \ - ".pushsection .altinstr_replacement, \"a\"\n" \ + ".subsection 1\n" \ "663:\n\t" \ newinstr "\n" \ "664:\n\t" \ - ".popsection\n\t" \ + ".previous\n\t" \ ".org . - (664b-663b) + (662b-661b)\n\t" \ ".org . - (662b-661b) + (664b-663b)\n" \ ".endif\n" @@ -117,9 +117,9 @@ static inline void apply_alternatives_module(void *start, size_t length) { } 662: .pushsection .altinstructions, "a" altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f .popsection - .pushsection .altinstr_replacement, "ax" + .subsection 1 663: \insn2 -664: .popsection +664: .previous .org . - (664b-663b) + (662b-661b) .org . - (662b-661b) + (664b-663b) .endif @@ -160,7 +160,7 @@ static inline void apply_alternatives_module(void *start, size_t length) { } .pushsection .altinstructions, "a" altinstruction_entry 663f, 661f, \cap, 664f-663f, 662f-661f .popsection - .pushsection .altinstr_replacement, "ax" + .subsection 1 .align 2 /* So GAS knows label 661 is suitably aligned */ 661: .endm @@ -179,9 +179,9 @@ static inline void apply_alternatives_module(void *start, size_t length) { } .macro alternative_else 662: .if .Lasm_alt_mode==0 - .pushsection .altinstr_replacement, "ax" + .subsection 1 .else - .popsection + .previous .endif 663: .endm @@ -192,7 +192,7 @@ static inline void apply_alternatives_module(void *start, size_t length) { } .macro alternative_endif 664: .if .Lasm_alt_mode==0 - .popsection + .previous .endif .org . - (664b-663b) + (662b-661b) .org . - (662b-661b) + (664b-663b) diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 6827da7f3aa5..5423ffe0a987 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -165,9 +165,6 @@ SECTIONS *(.altinstructions) __alt_instructions_end = .; } - .altinstr_replacement : { - *(.altinstr_replacement) - } . = ALIGN(SEGMENT_ALIGN); __inittext_end = .; -- 2.17.1 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel