From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Rutland Subject: [PATCH 1/3] arm64: alternative: add auto-nop infrastructure Date: Wed, 7 Sep 2016 11:07:08 +0100 Message-ID: <1473242830-26246-2-git-send-email-mark.rutland@arm.com> References: <1473242830-26246-1-git-send-email-mark.rutland@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 381A74998D for ; Wed, 7 Sep 2016 05:59:11 -0400 (EDT) Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id bv56trS3omao for ; Wed, 7 Sep 2016 05:59:09 -0400 (EDT) Received: from foss.arm.com (foss.arm.com [217.140.101.70]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 4CAA349B47 for ; Wed, 7 Sep 2016 05:59:09 -0400 (EDT) In-Reply-To: <1473242830-26246-1-git-send-email-mark.rutland@arm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu To: linux-arm-kernel@lists.infradead.org Cc: marc.zyngier@arm.com, andre.przywara@arm.com, will.deacon@arm.com, dave.martin@arm.com, catalin.marinas@arm.com, kvmarm@lists.cs.columbia.edu List-Id: kvmarm@lists.cs.columbia.edu 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. Signed-off-by: Mark Rutland Cc: Andre Przywara Cc: Catalin Marinas Cc: Dave Martin Cc: James Morse Cc: Will Deacon --- arch/arm64/include/asm/alternative.h | 71 +++++++++++++++++++++++++++--------- 1 file changed, 54 insertions(+), 17 deletions(-) diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h index 8746ff6..4ddbf1c 100644 --- a/arch/arm64/include/asm/alternative.h +++ b/arch/arm64/include/asm/alternative.h @@ -90,34 +90,55 @@ void apply_alternatives(void *start, size_t length); .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 @@ -125,11 +146,27 @@ void apply_alternatives(void *start, size_t length); * 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 +.rept (662b-661b) / 4 + nop +.endr +alternative_endif +.endm + #define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...) \ alternative_insn insn1, insn2, cap, IS_ENABLED(cfg) -- 1.9.1 From mboxrd@z Thu Jan 1 00:00:00 1970 From: mark.rutland@arm.com (Mark Rutland) Date: Wed, 7 Sep 2016 11:07:08 +0100 Subject: [PATCH 1/3] arm64: alternative: add auto-nop infrastructure In-Reply-To: <1473242830-26246-1-git-send-email-mark.rutland@arm.com> References: <1473242830-26246-1-git-send-email-mark.rutland@arm.com> Message-ID: <1473242830-26246-2-git-send-email-mark.rutland@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. Signed-off-by: Mark Rutland Cc: Andre Przywara Cc: Catalin Marinas Cc: Dave Martin Cc: James Morse Cc: Will Deacon --- arch/arm64/include/asm/alternative.h | 71 +++++++++++++++++++++++++++--------- 1 file changed, 54 insertions(+), 17 deletions(-) diff --git a/arch/arm64/include/asm/alternative.h b/arch/arm64/include/asm/alternative.h index 8746ff6..4ddbf1c 100644 --- a/arch/arm64/include/asm/alternative.h +++ b/arch/arm64/include/asm/alternative.h @@ -90,34 +90,55 @@ void apply_alternatives(void *start, size_t length); .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 @@ -125,11 +146,27 @@ void apply_alternatives(void *start, size_t length); * 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 +.rept (662b-661b) / 4 + nop +.endr +alternative_endif +.endm + #define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...) \ alternative_insn insn1, insn2, cap, IS_ENABLED(cfg) -- 1.9.1