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[192.237.175.120]) by mx.google.com with ESMTPS id h9si7551969ilq.118.2019.10.31.08.11.34 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 31 Oct 2019 08:11:34 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of xen-devel-bounces@lists.xenproject.org designates 192.237.175.120 as permitted sender) client-ip=192.237.175.120; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of xen-devel-bounces@lists.xenproject.org designates 192.237.175.120 as permitted sender) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1iQC5N-0006xK-U1; Thu, 31 Oct 2019 15:10:05 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1iQC5M-0006wA-Bo for xen-devel@lists.xenproject.org; Thu, 31 Oct 2019 15:10:04 +0000 X-Inumbo-ID: 7de919de-fbf0-11e9-a531-bc764e2007e4 Received: from foss.arm.com (unknown [217.140.110.172]) by us1-rack-iad1.inumbo.com (Halon) with ESMTP id 7de919de-fbf0-11e9-a531-bc764e2007e4; Thu, 31 Oct 2019 15:09:53 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 38BAA7CD; Thu, 31 Oct 2019 08:09:53 -0700 (PDT) Received: from e108454-lin.cambridge.arm.com (unknown [10.1.196.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EF0283F71E; Thu, 31 Oct 2019 08:09:51 -0700 (PDT) From: Julien Grall To: xen-devel@lists.xenproject.org Date: Thu, 31 Oct 2019 15:09:19 +0000 Message-Id: <20191031150922.22938-17-julien.grall@arm.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20191031150922.22938-1-julien.grall@arm.com> References: <20191031150922.22938-1-julien.grall@arm.com> Subject: [Xen-devel] [PATCH for-4.13 v4 16/19] xen/arm: alternative: add auto-nop infrastructure X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: jgross@suse.com, Mark Rutland , Stefano Stabellini , Julien Grall , Will Deacon , Julien Grall , Volodymyr Babchuk MIME-Version: 1.0 Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" From: Mark Rutland In some cases, one side of an alternative sequence is simply a number of NOPs used to balance the other side. Keeping track of this manually is tedious, and the presence of large chains of NOPs makes the code more painful to read than necessary. To ameliorate matters, this patch adds a new alternative_else_nop_endif, which automatically balances an alternative sequence with a trivial NOP sled. In many cases, we would like a NOP-sled in the default case, and instructions patched in in the presence of a feature. To enable the NOPs to be generated automatically for this case, this patch also adds a new alternative_if, and updates alternative_else and alternative_endif to work with either alternative_if or alternative_endif. The alternative infrastructure was originally ported from Linux. So this is pretty much a straight backport from commit 792d47379f4d "arm64: alternative: add auto-nop infrastructure". The only difference is the nops macro added as not yet existing in Xen. Signed-off-by: Mark Rutland [will: use new nops macro to generate nop sequences] Signed-off-by: Will Deacon [julien: Add nops and port to Xen] Signed-off-by: Julien Grall Reviewed-by: Volodymyr Babchuk Acked-by: Stefano Stabellini --- Changes in v3: - Add missing include to get auto-nop infrastructure build on arm32. Changes in v2: - Add Volodymyr's reviewed-by - Add Stefano's acked-by --- xen/include/asm-arm/alternative.h | 71 +++++++++++++++++++++++++++++---------- xen/include/asm-arm/macros.h | 7 ++++ 2 files changed, 61 insertions(+), 17 deletions(-) diff --git a/xen/include/asm-arm/alternative.h b/xen/include/asm-arm/alternative.h index 2830a6da2d..92e888aff8 100644 --- a/xen/include/asm-arm/alternative.h +++ b/xen/include/asm-arm/alternative.h @@ -2,6 +2,7 @@ #define __ASM_ALTERNATIVE_H #include +#include #define ARM_CB_PATCH ARM_NCAPS @@ -87,6 +88,7 @@ int apply_alternatives(const struct alt_instr *start, const struct alt_instr *en #else #include +#include .macro altinstruction_entry orig_offset alt_offset feature orig_len alt_len .word \orig_offset - . @@ -111,34 +113,55 @@ int apply_alternatives(const struct alt_instr *start, const struct alt_instr *en .endm /* - * Begin an alternative code sequence. + * Alternative sequences + * + * The code for the case where the capability is not present will be + * assembled and linked as normal. There are no restrictions on this + * code. + * + * The code for the case where the capability is present will be + * assembled into a special section to be used for dynamic patching. + * Code for that case must: + * + * 1. Be exactly the same length (in bytes) as the default code + * sequence. * - * The code that follows this macro will be assembled and linked as - * normal. There are no restrictions on this code. + * 2. Not contain a branch target that is used outside of the + * alternative sequence it is defined in (branches into an + * alternative sequence are not fixed up). + */ + +/* + * Begin an alternative code sequence. */ .macro alternative_if_not cap + .set .Lasm_alt_mode, 0 .pushsection .altinstructions, "a" altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f .popsection 661: .endm +.macro alternative_if cap + .set .Lasm_alt_mode, 1 + .pushsection .altinstructions, "a" + altinstruction_entry 663f, 661f, \cap, 664f-663f, 662f-661f + .popsection + .pushsection .altinstr_replacement, "ax" + .align 2 /* So GAS knows label 661 is suitably aligned */ +661: +.endm + /* - * Provide the alternative code sequence. - * - * The code that follows this macro is assembled into a special - * section to be used for dynamic patching. Code that follows this - * macro must: - * - * 1. Be exactly the same length (in bytes) as the default code - * sequence. - * - * 2. Not contain a branch target that is used outside of the - * alternative sequence it is defined in (branches into an - * alternative sequence are not fixed up). + * Provide the other half of the alternative code sequence. */ .macro alternative_else -662: .pushsection .altinstr_replacement, "ax" +662: + .if .Lasm_alt_mode==0 + .pushsection .altinstr_replacement, "ax" + .else + .popsection + .endif 663: .endm @@ -154,12 +177,26 @@ int apply_alternatives(const struct alt_instr *start, const struct alt_instr *en * Complete an alternative code sequence. */ .macro alternative_endif -664: .popsection +664: + .if .Lasm_alt_mode==0 + .popsection + .endif .org . - (664b-663b) + (662b-661b) .org . - (662b-661b) + (664b-663b) .endm /* + * Provides a trivial alternative or default sequence consisting solely + * of NOPs. The number of NOPs is chosen automatically to match the + * previous case. + */ +.macro alternative_else_nop_endif +alternative_else + nops (662b-661b) / ARCH_PATCH_INSN_SIZE +alternative_endif +.endm + +/* * Callback-based alternative epilogue */ .macro alternative_cb_end diff --git a/xen/include/asm-arm/macros.h b/xen/include/asm-arm/macros.h index 1d4bb41d15..91ea3505e4 100644 --- a/xen/include/asm-arm/macros.h +++ b/xen/include/asm-arm/macros.h @@ -13,4 +13,11 @@ # error "unknown ARM variant" #endif + /* NOP sequence */ + .macro nops, num + .rept \num + nop + .endr + .endm + #endif /* __ASM_ARM_MACROS_H */