[{"id":3682855,"web_url":"http://patchwork.ozlabs.org/comment/3682855/","msgid":"","date":"2026-04-27T17:58:51","subject":"Re: [RFC PATCH v1 7/9] x86: Add unsafe_copy_from_user()","submitter":{"id":92516,"url":"http://patchwork.ozlabs.org/api/people/92516/","name":"Yury Norov","email":"ynorov@nvidia.com"},"content":"On Mon, Apr 27, 2026 at 07:13:48PM +0200, Christophe Leroy (CS GROUP) wrote:\n> At the time being, x86 and arm64 are missing unsafe_copy_from_user().\n\nNo, they don't. They (should) rely on a generic implementation from\nlinux/uaccess.h, like every other arch, except for PPC and RISCV.\n\nBut they #define arch_unsafe_get_user, and the unsafe_copy_from_user()\nbecomes undefined conditionally on that.\n\nSo please, fix that bug instead of introducing another arch flavor.\nWe'd always choose generic version, unless there's strong evidence\nthat arch one is better. \n\n\nThanks,\nYury\n \n> Add it.\n> \n> Signed-off-by: Christophe Leroy (CS GROUP) \n> ---\n> arch/x86/include/asm/uaccess.h | 29 ++++++++++++++++++++++++-----\n> 1 file changed, 24 insertions(+), 5 deletions(-)\n> \n> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h\n> index 3a0dd3c2b233..10c458ffa399 100644\n> --- a/arch/x86/include/asm/uaccess.h\n> +++ b/arch/x86/include/asm/uaccess.h\n> @@ -598,7 +598,7 @@ _label:\t\t\t\t\t\t\t\t\t\\\n> * We want the unsafe accessors to always be inlined and use\n> * the error labels - thus the macro games.\n> */\n> -#define unsafe_copy_loop(dst, src, len, type, label)\t\t\t\t\\\n> +#define unsafe_put_loop(dst, src, len, type, label)\t\t\t\t\\\n> \twhile (len >= sizeof(type)) {\t\t\t\t\t\t\\\n> \t\tunsafe_put_user(*(type *)(src),(type __user *)(dst),label);\t\\\n> \t\tdst += sizeof(type);\t\t\t\t\t\t\\\n> @@ -611,10 +611,29 @@ do {\t\t\t\t\t\t\t\t\t\\\n> \tchar __user *__ucu_dst = (_dst);\t\t\t\t\\\n> \tconst char *__ucu_src = (_src);\t\t\t\t\t\\\n> \tsize_t __ucu_len = (_len);\t\t\t\t\t\\\n> -\tunsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);\t\\\n> -\tunsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);\t\\\n> -\tunsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);\t\\\n> -\tunsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);\t\\\n> +\tunsafe_put_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);\t\\\n> +\tunsafe_put_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);\t\\\n> +\tunsafe_put_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);\t\\\n> +\tunsafe_put_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);\t\\\n> +} while (0)\n> +\n> +#define unsafe_get_loop(dst, src, len, type, label)\t\t\t\t\\\n> +\twhile (len >= sizeof(type)) {\t\t\t\t\t\t\\\n> +\t\tunsafe_get_user(*(type __user *)(src),(type *)(dst),label);\t\\\n> +\t\tdst += sizeof(type);\t\t\t\t\t\t\\\n> +\t\tsrc += sizeof(type);\t\t\t\t\t\t\\\n> +\t\tlen -= sizeof(type);\t\t\t\t\t\t\\\n> +\t}\n> +\n> +#define unsafe_copy_from_user(_dst,_src,_len,label)\t\t\t\\\n> +do {\t\t\t\t\t\t\t\t\t\\\n> +\tchar *__ucu_dst = (_dst);\t\t\t\t\t\\\n> +\tconst char __user *__ucu_src = (_src);\t\t\t\t\\\n> +\tsize_t __ucu_len = (_len);\t\t\t\t\t\\\n> +\tunsafe_get_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);\t\\\n> +\tunsafe_get_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);\t\\\n> +\tunsafe_get_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);\t\\\n> +\tunsafe_get_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);\t\\\n> } while (0)\n> \n> #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT\n> -- \n> 2.49.0\n>","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=Nvidia.com header.i=@Nvidia.com header.a=rsa-sha256\n header.s=selector2 header.b=JEzvcYXQ;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=112.213.38.117; helo=lists.ozlabs.org;\n envelope-from=linuxppc-dev+bounces-20185-incoming=patchwork.ozlabs.org@lists.ozlabs.org;\n receiver=patchwork.ozlabs.org)","lists.ozlabs.org;\n arc=pass smtp.remote-ip=\"2a01:111:f403:c100::f\" arc.chain=microsoft.com","lists.ozlabs.org;\n dmarc=pass (p=reject dis=none) header.from=nvidia.com","lists.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=Nvidia.com header.i=@Nvidia.com header.a=rsa-sha256\n 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c=relaxed/relaxed; d=Nvidia.com;\n s=selector2;\n h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck;\n bh=YWBdJXFvUsRNS535pCc24v4leweSht+XdLI4YB0XzRQ=;\n b=JEzvcYXQdwVjYZQlnStgbJQRfUGE245OkUv62d/erL7f0QOnr7fp+plL1zfa5mv2O11r5j+JLE5qQdINthQPR+Bj7wYWw46AWrQu/eYz6ED1n8xbwCAyvlDxh9XEzqZC2g1/3KWQVSH/DH18jJwgAfYkttpt/Blmd/pUHyEDc3Wkd3edhlrvX1h1qaZ6ZPmQk/87myHHQ3TrQ1ak0Xvkilcg5V0KT50UAZqYfZ39xcshyA39b5FsO98OY/S/YtJ/myHG6I+ftEFEH6NVP/B7k+6+4RVku7Lrcmp3zsQ+ArtGrvl5bXoyxfgJj2OT6m5rwYJbHAOe8gpGdj72kjww1Q==","Date":"Mon, 27 Apr 2026 13:58:51 -0400","From":"Yury Norov ","To":"\"Christophe Leroy (CS GROUP)\" ","Cc":"Andrew Morton ,\n\tLinus Torvalds ,\n\tDavid Laight ,\n\tThomas Gleixner , linux-alpha@vger.kernel.org,\n\tlinux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org,\n\tlinux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,\n\tlinuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org,\n\tlinux-riscv@lists.infradead.org, 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lists.ozlabs.org"}},{"id":3682865,"web_url":"http://patchwork.ozlabs.org/comment/3682865/","msgid":"<63a4d0f6-0eb3-48cd-9f98-bf7b223b2606@kernel.org>","date":"2026-04-27T18:20:38","subject":"Re: [RFC PATCH v1 7/9] x86: Add unsafe_copy_from_user()","submitter":{"id":92089,"url":"http://patchwork.ozlabs.org/api/people/92089/","name":"Christophe Leroy (CS GROUP)","email":"chleroy@kernel.org"},"content":"Le 27/04/2026 à 19:58, Yury Norov a écrit :\n> On Mon, Apr 27, 2026 at 07:13:48PM +0200, Christophe Leroy (CS GROUP) wrote:\n>> At the time being, x86 and arm64 are missing unsafe_copy_from_user().\n> \n> No, they don't. They (should) rely on a generic implementation from\n> linux/uaccess.h, like every other arch, except for PPC and RISCV.\n> \n> But they #define arch_unsafe_get_user, and the unsafe_copy_from_user()\n> becomes undefined conditionally on that.\n> \n> So please, fix that bug instead of introducing another arch flavor.\n> We'd always choose generic version, unless there's strong evidence\n> that arch one is better.\n\nBut they both implement the exact same unsafe_copy_to_user(). What is \nthe difference here ?\n\nShould that function become generic too ?\n\nChristophe\n\n> \n> \n> Thanks,\n> Yury\n> \n>> Add it.\n>>\n>> Signed-off-by: Christophe Leroy (CS GROUP) \n>> ---\n>> arch/x86/include/asm/uaccess.h | 29 ++++++++++++++++++++++++-----\n>> 1 file changed, 24 insertions(+), 5 deletions(-)\n>>\n>> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h\n>> index 3a0dd3c2b233..10c458ffa399 100644\n>> --- a/arch/x86/include/asm/uaccess.h\n>> +++ b/arch/x86/include/asm/uaccess.h\n>> @@ -598,7 +598,7 @@ _label:\t\t\t\t\t\t\t\t\t\\\n>> * We want the unsafe accessors to always be inlined and use\n>> * the error labels - thus the macro games.\n>> */\n>> -#define unsafe_copy_loop(dst, src, len, type, label)\t\t\t\t\\\n>> +#define unsafe_put_loop(dst, src, len, type, label)\t\t\t\t\\\n>> \twhile (len >= sizeof(type)) {\t\t\t\t\t\t\\\n>> \t\tunsafe_put_user(*(type *)(src),(type __user *)(dst),label);\t\\\n>> \t\tdst += sizeof(type);\t\t\t\t\t\t\\\n>> @@ -611,10 +611,29 @@ do {\t\t\t\t\t\t\t\t\t\\\n>> \tchar __user *__ucu_dst = (_dst);\t\t\t\t\\\n>> \tconst char *__ucu_src = (_src);\t\t\t\t\t\\\n>> \tsize_t __ucu_len = (_len);\t\t\t\t\t\\\n>> -\tunsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);\t\\\n>> -\tunsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);\t\\\n>> -\tunsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);\t\\\n>> -\tunsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);\t\\\n>> +\tunsafe_put_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);\t\\\n>> +\tunsafe_put_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);\t\\\n>> +\tunsafe_put_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);\t\\\n>> +\tunsafe_put_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);\t\\\n>> +} while (0)\n>> +\n>> +#define unsafe_get_loop(dst, src, len, type, label)\t\t\t\t\\\n>> +\twhile (len >= sizeof(type)) {\t\t\t\t\t\t\\\n>> +\t\tunsafe_get_user(*(type __user *)(src),(type *)(dst),label);\t\\\n>> +\t\tdst += sizeof(type);\t\t\t\t\t\t\\\n>> +\t\tsrc += sizeof(type);\t\t\t\t\t\t\\\n>> +\t\tlen -= sizeof(type);\t\t\t\t\t\t\\\n>> +\t}\n>> +\n>> +#define unsafe_copy_from_user(_dst,_src,_len,label)\t\t\t\\\n>> +do {\t\t\t\t\t\t\t\t\t\\\n>> +\tchar *__ucu_dst = (_dst);\t\t\t\t\t\\\n>> +\tconst char __user *__ucu_src = (_src);\t\t\t\t\\\n>> +\tsize_t __ucu_len = (_len);\t\t\t\t\t\\\n>> +\tunsafe_get_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);\t\\\n>> +\tunsafe_get_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);\t\\\n>> +\tunsafe_get_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);\t\\\n>> +\tunsafe_get_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);\t\\\n>> } while (0)\n>> \n>> #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT\n>> -- \n>> 2.49.0\n>>","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256\n header.s=k20201202 header.b=J2scZpbK;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=2404:9400:21b9:f100::1; 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charset=UTF-8; format=flowed","Content-Transfer-Encoding":"8bit","X-Spam-Status":"No, score=-0.2 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED,\n\tDKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS\n\tautolearn=disabled version=4.0.1","X-Spam-Checker-Version":"SpamAssassin 4.0.1 (2024-03-25) on lists.ozlabs.org"}},{"id":3682905,"web_url":"http://patchwork.ozlabs.org/comment/3682905/","msgid":"","date":"2026-04-27T19:19:36","subject":"Re: [RFC PATCH v1 7/9] x86: Add unsafe_copy_from_user()","submitter":{"id":92516,"url":"http://patchwork.ozlabs.org/api/people/92516/","name":"Yury Norov","email":"ynorov@nvidia.com"},"content":"On Mon, Apr 27, 2026 at 08:20:38PM +0200, Christophe Leroy (CS GROUP) wrote:\n> \n> \n> Le 27/04/2026 à 19:58, Yury Norov a écrit :\n> > On Mon, Apr 27, 2026 at 07:13:48PM +0200, Christophe Leroy (CS GROUP) wrote:\n> > > At the time being, x86 and arm64 are missing unsafe_copy_from_user().\n> > \n> > No, they don't. They (should) rely on a generic implementation from\n> > linux/uaccess.h, like every other arch, except for PPC and RISCV.\n> > \n> > But they #define arch_unsafe_get_user, and the unsafe_copy_from_user()\n> > becomes undefined conditionally on that.\n> > \n> > So please, fix that bug instead of introducing another arch flavor.\n> > We'd always choose generic version, unless there's strong evidence\n> > that arch one is better.\n> \n> But they both implement the exact same unsafe_copy_to_user(). What is the\n> difference here ?\n>\n> Should that function become generic too ?\n\nThis is what Linus said when added x86 implementation for copy_from_user()\nin c512c69187197:\n\n Note that it only does this [arch version] for the copying _to_ user space,\n and we still don't have a unsafe version of copy_from_user().\n \n That's partly because we have no current users of it, but also partly\n because the copy_from_user() case is slightly different and cannot\n efficiently be implemented in terms of a unsafe_get_user() loop (because\n gcc can't do asm goto with outputs).\n\nIn the unsafe_copy_to_user case, arch versions were justified. Just as\nsaid, I'm not against arch version for unsafe_copy_from_user(), but it\nshould be explained very well.","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=fail reason=\"signature verification failed\" (2048-bit key;\n unprotected) header.d=Nvidia.com header.i=@Nvidia.com header.a=rsa-sha256\n header.s=selector2 header.b=YPchTHpL;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=2404:9400:21b9:f100::1; helo=lists.ozlabs.org;\n envelope-from=linuxppc-dev+bounces-20191-incoming=patchwork.ozlabs.org@lists.ozlabs.org;\n receiver=patchwork.ozlabs.org)","lists.ozlabs.org;\n arc=fail smtp.remote-ip=\"2a01:111:f403:c110::1\"","lists.ozlabs.org;\n dmarc=pass (p=reject dis=none) header.from=nvidia.com","lists.ozlabs.org;\n\tdkim=fail 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kvm@vger.kernel.org,\n\tlinux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,\n\tsparclinux@vger.kernel.org, linux-um@lists.infradead.org,\n\tdmaengine@vger.kernel.org, linux-efi@vger.kernel.org,\n\tlinux-fsi@lists.ozlabs.org, amd-gfx@lists.freedesktop.org,\n\tdri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org,\n\tlinux-wpan@vger.kernel.org, netdev@vger.kernel.org,\n\tlinux-wireless@vger.kernel.org, linux-spi@vger.kernel.org,\n\tlinux-media@vger.kernel.org, linux-staging@lists.linux.dev,\n\tlinux-serial@vger.kernel.org, linux-usb@vger.kernel.org,\n\txen-devel@lists.xenproject.org, linux-fsdevel@vger.kernel.org,\n\tocfs2-devel@lists.linux.dev, bpf@vger.kernel.org,\n\tkasan-dev@googlegroups.com, linux-mm@kvack.org,\n\tlinux-x25@vger.kernel.org, rust-for-linux@vger.kernel.org,\n\tlinux-sound@vger.kernel.org, sound-open-firmware@alsa-project.org,\n\tlinux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org,\n\tloongarch@lists.linux.dev, 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lists.ozlabs.org"}},{"id":3683019,"web_url":"http://patchwork.ozlabs.org/comment/3683019/","msgid":"","date":"2026-04-27T21:52:05","subject":"Re: [RFC PATCH v1 7/9] x86: Add unsafe_copy_from_user()","submitter":{"id":97,"url":"http://patchwork.ozlabs.org/api/people/97/","name":"Linus Torvalds","email":"torvalds@linux-foundation.org"},"content":"On Mon, 27 Apr 2026 at 12:19, Yury Norov wrote:\n>\n> This is what Linus said when added x86 implementation for copy_from_user()\n> in c512c69187197:\n\nNote that some things have happily changed in the six+ years since...\n\n> That's partly because we have no current users of it, but also partly\n> because the copy_from_user() case is slightly different and cannot\n> efficiently be implemented in terms of a unsafe_get_user() loop (because\n> gcc can't do asm goto with outputs).\n\nnow everybody can do asm goto with outputs.\n\nYes, it's disabled on older versions, so it's not *always* available,\nbut all modern versions do it. And if you care about performance, you\nwon't be using an old compiler.\n\n Linus","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=linux-foundation.org header.i=@linux-foundation.org\n header.a=rsa-sha256 header.s=google header.b=WU8PKBa0;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=112.213.38.117; helo=lists.ozlabs.org;\n envelope-from=linuxppc-dev+bounces-20197-incoming=patchwork.ozlabs.org@lists.ozlabs.org;\n receiver=patchwork.ozlabs.org)","lists.ozlabs.org;\n arc=none smtp.remote-ip=\"2a00:1450:4864:20::62a\"","lists.ozlabs.org;\n dmarc=none (p=none dis=none) header.from=linux-foundation.org","lists.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=linux-foundation.org header.i=@linux-foundation.org\n header.a=rsa-sha256 header.s=google header.b=WU8PKBa0;\n\tdkim-atps=neutral","lists.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=linuxfoundation.org\n (client-ip=2a00:1450:4864:20::62a; 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Mon, 27 Apr 2026\n 14:52:22 -0700 (PDT)"],"X-Mailing-List":"linuxppc-dev@lists.ozlabs.org","List-Id":"","List-Help":"","List-Owner":"","List-Post":"","List-Archive":",\n ","List-Subscribe":",\n ,\n ","List-Unsubscribe":"","Precedence":"list","MIME-Version":"1.0","References":"\n <0ee46bb228d97163fbdc14f2a7c52b93d8bc34ce.1777306795.git.chleroy@kernel.org>\n <63a4d0f6-0eb3-48cd-9f98-bf7b223b2606@kernel.org>\n ","In-Reply-To":"","From":"Linus Torvalds ","Date":"Mon, 27 Apr 2026 14:52:05 -0700","X-Gmail-Original-Message-ID":"\n ","X-Gm-Features":"AVHnY4LQUFWo9ODz4M3q2vZC9Gn8nsdYr95Nd4ky5ERVHHxIyN_9ZXY5zjebfdc","Message-ID":"\n ","Subject":"Re: [RFC PATCH v1 7/9] x86: Add unsafe_copy_from_user()","To":"Yury Norov ","Cc":"\"Christophe Leroy (CS GROUP)\" ,\n Andrew Morton ,\n\tDavid Laight ,\n Thomas Gleixner ,\n\tlinux-alpha@vger.kernel.org, Yury Norov ,\n\tlinux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org,\n\tlinux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,\n\tlinuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org,\n\tlinux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,\n\tsparclinux@vger.kernel.org, linux-um@lists.infradead.org,\n\tdmaengine@vger.kernel.org, linux-efi@vger.kernel.org,\n\tlinux-fsi@lists.ozlabs.org, amd-gfx@lists.freedesktop.org,\n\tdri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org,\n\tlinux-wpan@vger.kernel.org, netdev@vger.kernel.org,\n\tlinux-wireless@vger.kernel.org, linux-spi@vger.kernel.org,\n\tlinux-media@vger.kernel.org, linux-staging@lists.linux.dev,\n\tlinux-serial@vger.kernel.org, linux-usb@vger.kernel.org,\n\txen-devel@lists.xenproject.org, linux-fsdevel@vger.kernel.org,\n\tocfs2-devel@lists.linux.dev, bpf@vger.kernel.org, kasan-dev@googlegroups.com,\n\tlinux-mm@kvack.org, linux-x25@vger.kernel.org,\n rust-for-linux@vger.kernel.org,\n\tlinux-sound@vger.kernel.org, sound-open-firmware@alsa-project.org,\n\tlinux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org,\n\tloongarch@lists.linux.dev, linux-m68k@lists.linux-m68k.org,\n\tlinux-openrisc@vger.kernel.org, linux-parisc@vger.kernel.org,\n\tlinux-sh@vger.kernel.org, linux-arch@vger.kernel.org","Content-Type":"text/plain; charset=\"UTF-8\"","X-Spam-Status":"No, score=-0.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID,\n\tDKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_NONE,\n\tSPF_HELO_NONE,SPF_PASS autolearn=disabled version=4.0.1 OzLabs 8","X-Spam-Checker-Version":"SpamAssassin 4.0.1 (2024-03-25) on lists.ozlabs.org"}},{"id":3683034,"web_url":"http://patchwork.ozlabs.org/comment/3683034/","msgid":"","date":"2026-04-27T22:30:16","subject":"Re: [RFC PATCH v1 7/9] x86: Add unsafe_copy_from_user()","submitter":{"id":92516,"url":"http://patchwork.ozlabs.org/api/people/92516/","name":"Yury Norov","email":"ynorov@nvidia.com"},"content":"On Mon, Apr 27, 2026 at 02:52:05PM -0700, Linus Torvalds wrote:\n> On Mon, 27 Apr 2026 at 12:19, Yury Norov wrote:\n> >\n> > This is what Linus said when added x86 implementation for copy_from_user()\n> > in c512c69187197:\n> \n> Note that some things have happily changed in the six+ years since...\n> \n> > That's partly because we have no current users of it, but also partly\n> > because the copy_from_user() case is slightly different and cannot\n> > efficiently be implemented in terms of a unsafe_get_user() loop (because\n> > gcc can't do asm goto with outputs).\n> \n> now everybody can do asm goto with outputs.\n> \n> Yes, it's disabled on older versions, so it's not *always* available,\n> but all modern versions do it. And if you care about performance, you\n> won't be using an old compiler.\n\nThe minimal GCC version is 8.1, and asm goto with outputs is supported\nsince GCC-11. That would brake the build, if we just switch to using it\nwithout \"CC_IS_GCC && (GCC_VERSION >= 110100)\" guard.\n\nIs it worth to maintain 2 version of the function? I don't know...\n\nThanks,\nYury","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=Nvidia.com header.i=@Nvidia.com header.a=rsa-sha256\n header.s=selector2 header.b=nMn9Mg2e;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=2404:9400:21b9:f100::1; helo=lists.ozlabs.org;\n envelope-from=linuxppc-dev+bounces-20198-incoming=patchwork.ozlabs.org@lists.ozlabs.org;\n receiver=patchwork.ozlabs.org)","lists.ozlabs.org;\n arc=pass smtp.remote-ip=\"2a01:111:f403:c110::1\" arc.chain=microsoft.com","lists.ozlabs.org;\n dmarc=pass (p=reject dis=none) header.from=nvidia.com","lists.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=Nvidia.com header.i=@Nvidia.com header.a=rsa-sha256\n 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linux-s390@vger.kernel.org,\n\tsparclinux@vger.kernel.org, linux-um@lists.infradead.org,\n\tdmaengine@vger.kernel.org, linux-efi@vger.kernel.org,\n\tlinux-fsi@lists.ozlabs.org, amd-gfx@lists.freedesktop.org,\n\tdri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org,\n\tlinux-wpan@vger.kernel.org, netdev@vger.kernel.org,\n\tlinux-wireless@vger.kernel.org, linux-spi@vger.kernel.org,\n\tlinux-media@vger.kernel.org, linux-staging@lists.linux.dev,\n\tlinux-serial@vger.kernel.org, linux-usb@vger.kernel.org,\n\txen-devel@lists.xenproject.org, linux-fsdevel@vger.kernel.org,\n\tocfs2-devel@lists.linux.dev, bpf@vger.kernel.org,\n\tkasan-dev@googlegroups.com, linux-mm@kvack.org,\n\tlinux-x25@vger.kernel.org, rust-for-linux@vger.kernel.org,\n\tlinux-sound@vger.kernel.org, sound-open-firmware@alsa-project.org,\n\tlinux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org,\n\tloongarch@lists.linux.dev, linux-m68k@lists.linux-m68k.org,\n\tlinux-openrisc@vger.kernel.org, linux-parisc@vger.kernel.org,\n\tlinux-sh@vger.kernel.org, linux-arch@vger.kernel.org","Subject":"Re: [RFC PATCH v1 7/9] x86: Add unsafe_copy_from_user()","Message-ID":"","References":"\n <0ee46bb228d97163fbdc14f2a7c52b93d8bc34ce.1777306795.git.chleroy@kernel.org>\n \n <63a4d0f6-0eb3-48cd-9f98-bf7b223b2606@kernel.org>\n \n ","Content-Type":"text/plain; charset=us-ascii","Content-Disposition":"inline","In-Reply-To":"\n ","X-ClientProxiedBy":"BN0PR04CA0197.namprd04.prod.outlook.com\n (2603:10b6:408:e9::22) To CY8PR12MB8300.namprd12.prod.outlook.com\n (2603:10b6:930:7d::16)","X-Mailing-List":"linuxppc-dev@lists.ozlabs.org","List-Id":"","List-Help":"","List-Owner":"","List-Post":"","List-Archive":",\n ","List-Subscribe":",\n ,\n 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lists.ozlabs.org"}},{"id":3683395,"web_url":"http://patchwork.ozlabs.org/comment/3683395/","msgid":"","date":"2026-04-28T11:20:17","subject":"Re: [RFC PATCH v1 7/9] x86: Add unsafe_copy_from_user()","submitter":{"id":134,"url":"http://patchwork.ozlabs.org/api/people/134/","name":"Segher Boessenkool","email":"segher@kernel.crashing.org"},"content":"Hi!\n\nOn Mon, Apr 27, 2026 at 06:30:16PM -0400, Yury Norov wrote:\n> On Mon, Apr 27, 2026 at 02:52:05PM -0700, Linus Torvalds wrote:\n> > On Mon, 27 Apr 2026 at 12:19, Yury Norov wrote:\n> > >\n> > > This is what Linus said when added x86 implementation for copy_from_user()\n> > > in c512c69187197:\n> > \n> > Note that some things have happily changed in the six+ years since...\n> > \n> > > That's partly because we have no current users of it, but also partly\n> > > because the copy_from_user() case is slightly different and cannot\n> > > efficiently be implemented in terms of a unsafe_get_user() loop (because\n> > > gcc can't do asm goto with outputs).\n> > \n> > now everybody can do asm goto with outputs.\n> > \n> > Yes, it's disabled on older versions, so it's not *always* available,\n> > but all modern versions do it. And if you care about performance, you\n> > won't be using an old compiler.\n> \n> The minimal GCC version is 8.1, and asm goto with outputs is supported\n> since GCC-11. That would brake the build, if we just switch to using it\n> without \"CC_IS_GCC && (GCC_VERSION >= 110100)\" guard.\n> \n> Is it worth to maintain 2 version of the function? I don't know...\n\nGCC 11 was released five years and a day ago. The last GCC 11 release\n(that of 11.5) is not even two years ago though (but there will be no\nmore!)\n\nSo it would be not conservative at all to require GCC 11 as minimum now,\nsome people might even call it a bit aggressive. But in a year (or\nmaybe two) the lay of the land will be rather different.\n\n\nSegher","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=2404:9400:21b9:f100::1; helo=lists.ozlabs.org;\n envelope-from=linuxppc-dev+bounces-20234-incoming=patchwork.ozlabs.org@lists.ozlabs.org;\n receiver=patchwork.ozlabs.org)","lists.ozlabs.org; arc=none smtp.remote-ip=63.228.1.57","lists.ozlabs.org;\n dmarc=none (p=none dis=none) header.from=kernel.crashing.org","lists.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=kernel.crashing.org\n (client-ip=63.228.1.57; helo=gate.crashing.org;\n envelope-from=segher@kernel.crashing.org; receiver=lists.ozlabs.org)"],"Received":["from lists.ozlabs.org (lists.ozlabs.org\n [IPv6:2404:9400:21b9:f100::1])\n\t(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n\t key-exchange x25519)\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4g4dKs68nKz1yHv\n\tfor ; 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