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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E973C433F5 for ; Mon, 29 Nov 2021 07:24:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236730AbhK2H1m (ORCPT ); Mon, 29 Nov 2021 02:27:42 -0500 Received: from pegase2.c-s.fr ([93.17.235.10]:58935 "EHLO pegase2.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229777AbhK2HZl (ORCPT ); Mon, 29 Nov 2021 02:25:41 -0500 Received: from localhost (mailhub3.si.c-s.fr [172.26.127.67]) by localhost (Postfix) with ESMTP id 4J2cHg211vz9sSk; Mon, 29 Nov 2021 08:22:23 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from pegase2.c-s.fr ([172.26.127.65]) by localhost (pegase2.c-s.fr [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id UPVQNJoArrEd; Mon, 29 Nov 2021 08:22:23 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase2.c-s.fr (Postfix) with ESMTP id 4J2cHg1BMJz9sSh; Mon, 29 Nov 2021 08:22:23 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 19C2D8B76D; Mon, 29 Nov 2021 08:22:23 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id 95kUX8e7kcKx; Mon, 29 Nov 2021 08:22:23 +0100 (CET) Received: from [172.25.230.108] (unknown [172.25.230.108]) by messagerie.si.c-s.fr (Postfix) with ESMTP id BD33C8B763; Mon, 29 Nov 2021 08:22:22 +0100 (CET) Message-ID: Date: Mon, 29 Nov 2021 08:22:22 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Subject: Re: [PATCH v3 4/4] powerpc/inst: Optimise copy_inst_from_kernel_nofault() Content-Language: fr-FR To: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org References: <1a8623dce54a72c7af172027caa7c44b1fefa8c4.1638036607.git.christophe.leroy@csgroup.eu> From: Christophe Leroy In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 27/11/2021 à 19:10, Christophe Leroy a écrit : > copy_inst_from_kernel_nofault() uses copy_from_kernel_nofault() to > copy one or two 32bits words. This means calling an out-of-line > function which itself calls back copy_from_kernel_nofault_allowed() > then performs a generic copy with loops. > > Rewrite copy_inst_from_kernel_nofault() to do everything at a > single place and use __get_kernel_nofault() directly to perform > single accesses without loops. > > Before the patch: > > 00000018 : > 18: 94 21 ff e0 stwu r1,-32(r1) > 1c: 7c 08 02 a6 mflr r0 > 20: 38 a0 00 04 li r5,4 > 24: 93 e1 00 1c stw r31,28(r1) > 28: 7c 7f 1b 78 mr r31,r3 > 2c: 38 61 00 08 addi r3,r1,8 > 30: 90 01 00 24 stw r0,36(r1) > 34: 48 00 00 01 bl 34 > 34: R_PPC_REL24 copy_from_kernel_nofault > 38: 2c 03 00 00 cmpwi r3,0 > 3c: 40 82 00 0c bne 48 > 40: 81 21 00 08 lwz r9,8(r1) > 44: 91 3f 00 00 stw r9,0(r31) > 48: 80 01 00 24 lwz r0,36(r1) > 4c: 83 e1 00 1c lwz r31,28(r1) > 50: 38 21 00 20 addi r1,r1,32 > 54: 7c 08 03 a6 mtlr r0 > 58: 4e 80 00 20 blr > > After the patch: > > 00000018 : > 18: 3d 20 b0 00 lis r9,-20480 > 1c: 7c 04 48 40 cmplw r4,r9 > 20: 7c 69 1b 78 mr r9,r3 > 24: 41 80 00 2c blt 50 > 28: 81 42 04 d0 lwz r10,1232(r2) > 2c: 39 4a 00 01 addi r10,r10,1 > 30: 91 42 04 d0 stw r10,1232(r2) > 34: 80 e4 00 00 lwz r7,0(r4) > 38: 81 42 04 d0 lwz r10,1232(r2) > 3c: 38 60 00 00 li r3,0 > 40: 39 4a ff ff addi r10,r10,-1 > 44: 91 42 04 d0 stw r10,1232(r2) > 48: 90 e9 00 00 stw r7,0(r9) > 4c: 4e 80 00 20 blr > > 50: 38 60 ff de li r3,-34 > 54: 4e 80 00 20 blr > 58: 81 22 04 d0 lwz r9,1232(r2) > 5c: 38 60 ff f2 li r3,-14 > 60: 39 29 ff ff addi r9,r9,-1 > 64: 91 22 04 d0 stw r9,1232(r2) > 68: 4e 80 00 20 blr > > Signed-off-by: Christophe Leroy > --- > v3: New > --- > arch/powerpc/mm/maccess.c | 18 ++++++++++++------ > 1 file changed, 12 insertions(+), 6 deletions(-) > > diff --git a/arch/powerpc/mm/maccess.c b/arch/powerpc/mm/maccess.c > index 5abae96b2b46..90309806f5eb 100644 > --- a/arch/powerpc/mm/maccess.c > +++ b/arch/powerpc/mm/maccess.c > @@ -15,16 +15,22 @@ bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size) > int copy_inst_from_kernel_nofault(ppc_inst_t *inst, u32 *src) > { > unsigned int val, suffix; > - int err; > > - err = copy_from_kernel_nofault(&val, src, sizeof(val)); > - if (err) > - return err; > + if (unlikely(!is_kernel_addr((unsigned long)src))) > + return -ERANGE; > + > + pagefault_disable(); Allthough generic version of copy_from_kernel_nofault() does it, disabling pagefault is pointless here because we are accessing kernel addresses only, so a page fault will always fail via bad_kernel_fault(), it will never reach the faulthandler_disabled() test. > + __get_kernel_nofault(&val, src, u32, Efault); > if (IS_ENABLED(CONFIG_PPC64) && get_op(val) == OP_PREFIX) { > - err = copy_from_kernel_nofault(&suffix, src + 1, sizeof(suffix)); > + __get_kernel_nofault(&suffix, src + 1, u32, Efault); > + pagefault_enable(); > *inst = ppc_inst_prefix(val, suffix); > } else { > + pagefault_enable(); > *inst = ppc_inst(val); > } > - return err; > + return 0; > +Efault: > + pagefault_enable(); > + return -EFAULT; > } >