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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 206EBC5B552 for ; Mon, 9 Jun 2025 11:01:09 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4bG89c3ZNwz2xlL; Mon, 9 Jun 2025 21:01:08 +1000 (AEST) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip=195.135.223.131 ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1749466868; cv=none; b=XMhKSHwkers23CRi2Z2LUMzlAZfRwWy7KGVW2GBQoUPRS4RJ+qj1n4omAPK1PVQ0YSZogTHaMGa3KW2Bgas/3kTcnFs5J0BqZkWsFFIblw5UoQg/xGwCOnVzZ0YisYq/UBk0fRO/uUz/xMd7XpFM1k9bFI2J+bY7AwC5jGo0jLHgBx0VaN9DA7UissfNsq3d9bTqo/vK6HiXqczv0a89sYzM+pGLzxmc7+ctTiXiOlJ1o1hVJ7As0MuE1SXpQF6ohZJxPXEM1B+NoTffqHgwVkyMNIYz74DrmkRbeLbBJjMmd8y8ShbGLNzVLPlpnAO0BArU9XkfS0TdA8xol6WUeA== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1749466868; c=relaxed/relaxed; bh=AYDkissmsxsA6CZ2/OeDcVyhcRKbhFLuEAjl5FIP/C4=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=TKU+0xviPRHCxmVLdOU1zE25QEq287w6V6H1kPrE40lIChFRd/yUy26XKVXpqSz4JdYrkrOWcZGz3PdLe+vkxkCtCOozrVOKO/JlAO+g6Oi0mA22QNsqzMUWNkQsonwLR1A71pZxNoO0oHz4Yx1lq+71vU2IITQlyKp+fLJI4SAkBBHyolnGbRR09ninZ7i7e2bu+s9Kdmx/gb2iOlPsEpMiuJrjcPNAjyJnCRyjUQ2ITLX1p6L3Vl0WMb/G7E9X/tHGoWu866muKmrhHs42OJLoVVxW0Qr1mHm4418W6aXm9BQh7disVLfZ7S4ffui6TFuNkkou6zLsZlTnVuOujw== ARC-Authentication-Results: i=1; lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=suse.de; dkim=pass (1024-bit key; unprotected) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=GgAQO5Gd; dkim=pass header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=RaUrq8tV; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=GgAQO5Gd; dkim=neutral header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=RaUrq8tV; dkim-atps=neutral; spf=pass (client-ip=195.135.223.131; helo=smtp-out2.suse.de; envelope-from=tiwai@suse.de; receiver=lists.ozlabs.org) smtp.mailfrom=suse.de Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=suse.de Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=GgAQO5Gd; dkim=pass header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=RaUrq8tV; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=GgAQO5Gd; dkim=neutral header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=RaUrq8tV; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=suse.de (client-ip=195.135.223.131; helo=smtp-out2.suse.de; envelope-from=tiwai@suse.de; receiver=lists.ozlabs.org) Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.223.131]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4bG89W4Xg2z2xgX for ; Mon, 9 Jun 2025 21:01:03 +1000 (AEST) Received: from imap1.dmz-prg2.suse.org (unknown [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 867DC1F443; Mon, 9 Jun 2025 11:01:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1749466860; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=AYDkissmsxsA6CZ2/OeDcVyhcRKbhFLuEAjl5FIP/C4=; b=GgAQO5GddygkhIYveM6lNCArjjp734Wcs5dP1KYd4BQpFd6dSur5NCnJeg4FG11IZKW+89 segwXyPdglI1cCwzQzEVBCI5q4IdafGmjyIwfwY9kWEs8IuHCMNNieaq1uunWtiUwDdJLu GToNpjkqp9kCHunIBchT5qHCXCbCBpE= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1749466860; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=AYDkissmsxsA6CZ2/OeDcVyhcRKbhFLuEAjl5FIP/C4=; b=RaUrq8tVarcHGkyzfrDfRtWMcIqJKoEs2FwkoTA87VIXWERbocthvYqqw7KITAKjnjXNKI cHB97qUoci3xLKDQ== Authentication-Results: smtp-out2.suse.de; none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1749466860; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=AYDkissmsxsA6CZ2/OeDcVyhcRKbhFLuEAjl5FIP/C4=; b=GgAQO5GddygkhIYveM6lNCArjjp734Wcs5dP1KYd4BQpFd6dSur5NCnJeg4FG11IZKW+89 segwXyPdglI1cCwzQzEVBCI5q4IdafGmjyIwfwY9kWEs8IuHCMNNieaq1uunWtiUwDdJLu GToNpjkqp9kCHunIBchT5qHCXCbCBpE= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1749466860; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=AYDkissmsxsA6CZ2/OeDcVyhcRKbhFLuEAjl5FIP/C4=; b=RaUrq8tVarcHGkyzfrDfRtWMcIqJKoEs2FwkoTA87VIXWERbocthvYqqw7KITAKjnjXNKI cHB97qUoci3xLKDQ== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 42B18137FE; Mon, 9 Jun 2025 11:01:00 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id ne9+Duy+RmgmNAAAD6G6ig (envelope-from ); Mon, 09 Jun 2025 11:01:00 +0000 Date: Mon, 09 Jun 2025 13:00:59 +0200 Message-ID: <87frg96uxg.wl-tiwai@suse.de> From: Takashi Iwai To: Christophe Leroy Cc: Takashi Iwai , Jaroslav Kysela , Takashi Iwai , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-sound@vger.kernel.org, Herve Codina , Mark Brown Subject: Re: [PATCH v2] ALSA: pcm: Convert multiple {get/put}_user to user_access_begin/user_access_end() In-Reply-To: <6fbbb13e-aedd-47ad-a58b-cc00e9ea138c@csgroup.eu> References: <87zfeh72sz.wl-tiwai@suse.de> <6fbbb13e-aedd-47ad-a58b-cc00e9ea138c@csgroup.eu> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-3.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_SEVEN(0.00)[9]; RCVD_TLS_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; TO_DN_SOME(0.00)[]; FROM_HAS_DN(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:mid] On Mon, 09 Jun 2025 12:02:00 +0200, Christophe Leroy wrote: > > > > Le 09/06/2025 à 10:10, Takashi Iwai a écrit : > > On Mon, 09 Jun 2025 10:00:38 +0200, > > Christophe Leroy wrote: > >> > >> With user access protection (Called SMAP on x86 or KUAP on powerpc) > >> each and every call to get_user() or put_user() performs heavy > >> operations to unlock and lock kernel access to userspace. > >> > >> To avoid that, perform user accesses by blocks using > >> user_access_begin/user_access_end() and unsafe_get_user()/ > >> unsafe_put_user() and alike. > >> > >> As an exemple, before the patch the 9 calls to put_user() at the > >> end of snd_pcm_ioctl_sync_ptr_compat() imply the following set of > >> instructions about 9 times (access_ok - enable user - write - disable > >> user): > >> 0.00 : c057f858: 3d 20 7f ff lis r9,32767 > >> 0.29 : c057f85c: 39 5e 00 14 addi r10,r30,20 > >> 0.77 : c057f860: 61 29 ff fc ori r9,r9,65532 > >> 0.32 : c057f864: 7c 0a 48 40 cmplw r10,r9 > >> 0.36 : c057f868: 41 a1 fb 58 bgt c057f3c0 > >> 0.30 : c057f86c: 3d 20 dc 00 lis r9,-9216 > >> 1.95 : c057f870: 7d 3a c3 a6 mtspr 794,r9 > >> 0.33 : c057f874: 92 8a 00 00 stw r20,0(r10) > >> 0.27 : c057f878: 3d 20 de 00 lis r9,-8704 > >> 0.28 : c057f87c: 7d 3a c3 a6 mtspr 794,r9 > >> ... > >> > >> A perf profile shows that in total the 9 put_user() represent 36% of > >> the time spent in snd_pcm_ioctl() and about 80 instructions. > >> > >> With this patch everything is done in 13 instructions and represent > >> only 15% of the time spent in snd_pcm_ioctl(): > >> > >> 0.57 : c057f5dc: 3d 20 dc 00 lis r9,-9216 > >> 0.98 : c057f5e0: 7d 3a c3 a6 mtspr 794,r9 > >> 0.16 : c057f5e4: 92 7f 00 04 stw r19,4(r31) > >> 0.63 : c057f5e8: 93 df 00 0c stw r30,12(r31) > >> 0.16 : c057f5ec: 93 9f 00 10 stw r28,16(r31) > >> 4.95 : c057f5f0: 92 9f 00 14 stw r20,20(r31) > >> 0.19 : c057f5f4: 92 5f 00 18 stw r18,24(r31) > >> 0.49 : c057f5f8: 92 bf 00 1c stw r21,28(r31) > >> 0.27 : c057f5fc: 93 7f 00 20 stw r27,32(r31) > >> 5.88 : c057f600: 93 36 00 00 stw r25,0(r22) > >> 0.11 : c057f604: 93 17 00 00 stw r24,0(r23) > >> 0.00 : c057f608: 3d 20 de 00 lis r9,-8704 > >> 0.79 : c057f60c: 7d 3a c3 a6 mtspr 794,r9 > >> > >> Note that here the access_ok() in user_write_access_begin() is skipped > >> because the exact same verification has already been performed at the > >> beginning of the fonction with the call to user_read_access_begin(). > >> > >> A couple more can be converted as well but require > >> unsafe_copy_from_user() which is not defined on x86 and arm64, so > >> those are left aside for the time being and will be handled in a > >> separate patch. > >> > >> Signed-off-by: Christophe Leroy > >> --- > >> v2: Split out the two hunks using copy_from_user() as unsafe_copy_from_user() is not implemented on x86 and arm64 yet. > > > > Thanks for the patch. > > > > The idea looks interesting, but the implementations with > > unsafe_get_user() leads to very ugly goto lines, and that's too bad; > > it makes the code flow much more difficult to follow. > > > > I guess that, in most cases this patch tries to cover, we just use > > another temporary variable for compat struct, copy fields locally, > > then run copy_to_user() in a shot instead. > > Thanks for looking. > > I'll give it a try but I think going through a local intermediate will > be less performant than direct copy with unsafe_get/put_user(). Yes, but the code readability is often more important than minor optimizations unless it's in a hot path. thanks, Takashi