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 X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9F97BC43465 for ; Sun, 20 Sep 2020 17:24:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5B75520866 for ; Sun, 20 Sep 2020 17:24:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="tzqY9X8f"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Ajg419VR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726055AbgITRYx (ORCPT ); Sun, 20 Sep 2020 13:24:53 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:46734 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725858AbgITRYx (ORCPT ); Sun, 20 Sep 2020 13:24:53 -0400 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1600622689; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ELUNMLCQYXoHQWzGjHTiBi/GvrgBrzUdsStDgdETjPA=; b=tzqY9X8fLvmtivfsbNK0pUu8YiUj7NKf7+bQzIN33nK/SwghNMa2rz52k7m9LEaGnDxB4p 5uJRP8jzSGhdLLpPzoF07YS1dppzeAHFuaRXBxkQ6eQFewoBrpPutv3yBGdR9YKqd5UnMc Lfw64Wh81l4jTzfijbUVM/G1PeB+l9wpVjsRPd3Xz3aQUHw9+Bu78ZLn5k1aNaH9Pkc5ms Lg9Dct8esi3AxOTl0URAWW4pIL6LMaz6yDqISWtV082sZby+eUJYHhPHZSuxMGdcllbxYl qQ/7nvxbGePtOn6SDA8Bi+zAxXBj+TvBWAwr7ALWt4wsGLJLJU/NhQ4k2+3KDg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1600622689; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ELUNMLCQYXoHQWzGjHTiBi/GvrgBrzUdsStDgdETjPA=; b=Ajg419VRwVNBaCnESvnWBGYX1dQ8DDFprO3wwe5+UvEno+/XgboH3A5bxhtY6hr785JAXL VPGuKWoChMzzg9BQ== To: Daniel Vetter Cc: Daniel Vetter , LKML , "open list\:GENERIC INCLUDE\/A..." , Linus Torvalds , Paul McKenney , X86 ML , Sebastian Andrzej Siewior , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Will Deacon , Andrew Morton , Linux-MM , Russell King , Linux ARM , Chris Zankel , Max Filippov , linux-xtensa@linux-xtensa.org, Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , David Airlie , intel-gfx , dri-devel , Ard Biesheuvel , Herbert Xu , Vineet Gupta , arcml , Arnd Bergmann , Guo Ren , linux-csky@vger.kernel.org, Michal Simek , Thomas Bogendoerfer , linux-mips@vger.kernel.org, Nick Hu , Greentime Hu , Vincent Chen , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev , "David S. Miller" , sparclinux@vger.kernel.org Subject: Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends In-Reply-To: <20200920082353.GG438822@phenom.ffwll.local> References: <20200919091751.011116649@linutronix.de> <87pn6hc6g1.fsf@nanos.tec.linutronix.de> <20200920082353.GG438822@phenom.ffwll.local> Date: Sun, 20 Sep 2020 19:24:49 +0200 Message-ID: <87h7rscqe6.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-csky@vger.kernel.org On Sun, Sep 20 2020 at 10:23, Daniel Vetter wrote: > On Sun, Sep 20, 2020 at 08:23:26AM +0200, Thomas Gleixner wrote: >> On Sat, Sep 19 2020 at 12:37, Daniel Vetter wrote: >> > On Sat, Sep 19, 2020 at 12:35 PM Daniel Vetter wrote: >> >> I think it should be the case, but I want to double check: Will >> >> copy_*_user be allowed within a kmap_temporary section? This would >> >> allow us to ditch an absolute pile of slowpaths. >> > >> > (coffee just kicked in) copy_*_user is ofc allowed, but if you hit a >> > page fault you get a short read/write. This looks like it would remove >> > the need to handle these in a slowpath, since page faults can now be >> > served in this new kmap_temporary sections. But this sounds too good >> > to be true, so I'm wondering what I'm missing. >> >> In principle we could allow pagefaults, but not with the currently >> proposed interface which can be called from any context. Obviously if >> called from atomic context it can't handle user page faults. > > Yeah that's clear, but does the implemention need to disable pagefaults > unconditionally? As I wrote in the other reply it's not required and the final interface will neither disable preemption nor pagefaults (except for the atomic wrapper around it). Thanks, tglx