From patchwork Fri Mar 27 13:09:22 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marc Zyngier X-Patchwork-Id: 6106961 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id D6A03BF90F for ; Fri, 27 Mar 2015 13:13:43 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id E8CED2028D for ; Fri, 27 Mar 2015 13:13:42 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D0B7F201B4 for ; Fri, 27 Mar 2015 13:13:41 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1YbU2a-00052E-T3; Fri, 27 Mar 2015 13:11:12 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1YbU1f-0003My-Qo for linux-arm-kernel@lists.infradead.org; Fri, 27 Mar 2015 13:10:17 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6F9B6581; Fri, 27 Mar 2015 06:09:58 -0700 (PDT) Received: from approximate.cambridge.arm.com (approximate.cambridge.arm.com [10.1.209.148]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 34CBA3F21B; Fri, 27 Mar 2015 06:09:54 -0700 (PDT) From: Marc Zyngier To: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu Subject: [PATCH v3 2/5] arm64: alternative: Allow immediate branch as alternative instruction Date: Fri, 27 Mar 2015 13:09:22 +0000 Message-Id: <1427461765-14462-3-git-send-email-marc.zyngier@arm.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1427461765-14462-1-git-send-email-marc.zyngier@arm.com> References: <1427461765-14462-1-git-send-email-marc.zyngier@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20150327_061016_045265_6B5882B1 X-CRM114-Status: GOOD ( 14.56 ) X-Spam-Score: -5.0 (-----) Cc: "Jon Medhurst \(Tixy\)" , Andre Przywara , Will Deacon , Catalin Marinas , Dave Martin , Christoffer Dall X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Since all immediate branches are PC-relative on Aarch64, these instructions cannot be used as an alternative with the simplistic approach we currently have (the immediate has been computed from the .altinstr_replacement section, and end-up being completely off if we insert it directly). This patch handles the b and bl instructions in a different way, using the insn framework to recompute the immediate, and generate the right displacement. Reviewed-by: Andre Przywara Acked-by: Will Deacon Signed-off-by: Marc Zyngier --- arch/arm64/kernel/alternative.c | 55 +++++++++++++++++++++++++++++++++++++++-- 1 file changed, 53 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c index ad7821d..21033bb 100644 --- a/arch/arm64/kernel/alternative.c +++ b/arch/arm64/kernel/alternative.c @@ -24,6 +24,7 @@ #include #include #include +#include #include extern struct alt_instr __alt_instructions[], __alt_instructions_end[]; @@ -33,6 +34,48 @@ struct alt_region { struct alt_instr *end; }; +/* + * Decode the imm field of a b/bl instruction, and return the byte + * offset as a signed value (so it can be used when computing a new + * branch target). + */ +static s32 get_branch_offset(u32 insn) +{ + s32 imm = aarch64_insn_decode_immediate(AARCH64_INSN_IMM_26, insn); + + /* sign-extend the immediate before turning it into a byte offset */ + return (imm << 6) >> 4; +} + +static u32 get_alt_insn(u8 *insnptr, u8 *altinsnptr) +{ + u32 insn; + + aarch64_insn_read(altinsnptr, &insn); + + /* Stop the world on instructions we don't support... */ + BUG_ON(aarch64_insn_is_cbz(insn)); + BUG_ON(aarch64_insn_is_cbnz(insn)); + BUG_ON(aarch64_insn_is_bcond(insn)); + /* ... and there is probably more. */ + + if (aarch64_insn_is_b(insn) || aarch64_insn_is_bl(insn)) { + enum aarch64_insn_branch_type type; + unsigned long target; + + if (aarch64_insn_is_b(insn)) + type = AARCH64_INSN_BRANCH_NOLINK; + else + type = AARCH64_INSN_BRANCH_LINK; + + target = (unsigned long)altinsnptr + get_branch_offset(insn); + insn = aarch64_insn_gen_branch_imm((unsigned long)insnptr, + target, type); + } + + return insn; +} + static int __apply_alternatives(void *alt_region) { struct alt_instr *alt; @@ -40,16 +83,24 @@ static int __apply_alternatives(void *alt_region) u8 *origptr, *replptr; for (alt = region->begin; alt < region->end; alt++) { + u32 insn; + int i; + if (!cpus_have_cap(alt->cpufeature)) continue; - BUG_ON(alt->alt_len > alt->orig_len); + BUG_ON(alt->alt_len != alt->orig_len); pr_info_once("patching kernel code\n"); origptr = (u8 *)&alt->orig_offset + alt->orig_offset; replptr = (u8 *)&alt->alt_offset + alt->alt_offset; - memcpy(origptr, replptr, alt->alt_len); + + for (i = 0; i < alt->alt_len; i += sizeof(insn)) { + insn = get_alt_insn(origptr + i, replptr + i); + aarch64_insn_write(origptr + i, insn); + } + flush_icache_range((uintptr_t)origptr, (uintptr_t)(origptr + alt->alt_len)); }