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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 C83B9C43468 for ; Sun, 20 Sep 2020 08:49:26 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 70D31214F1 for ; Sun, 20 Sep 2020 08:49:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="h8jv+ylt"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="ZMmhQ6D7" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 70D31214F1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9AD498966B; Sun, 20 Sep 2020 08:49:25 +0000 (UTC) Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by gabe.freedesktop.org (Postfix) with ESMTPS id 146F18966B; Sun, 20 Sep 2020 08:49:23 +0000 (UTC) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1600591762; 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=yl4SJva1ZaL/QSosb5XX7oiMR9yOUZ2hryRMeN6gUOs=; b=h8jv+yltDHIngnBBGJjPbxbwRp4WWvfUYCE010JZcD8mxV4UaeO8dLdDu13Q2cG+LY8JOQ h6npHbPhilGj3v1VUqWxvnxWjS/ksALdSUA+5C9fXgz9TR+62SaZPqFm9CDQlxwGmO5sxH Og/nMSeW9my8zlDQTOZZtLu/e9zkMmPgdx5NK5E8Rcfn4iS1ni7EpBlci97FKZLWMkER3O +JFJopKrMaT622cTfw+fq7PTs6AJTMpiNhuh5DlxWwRcA1+vumWCIqGRFavPq8Rwh2wOji LMGpm7pbhOs/2HMUMaIGkJEZas3RBbG5QRgXaIHLQPqkcnXaia1X2M3U1G452Q== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1600591762; 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=yl4SJva1ZaL/QSosb5XX7oiMR9yOUZ2hryRMeN6gUOs=; b=ZMmhQ6D75ka6LNiomg7OC2DwIv8yEqOFqmHU4LlJlX/duWyJlSPDqvfBsTbUq7MYp5KhFm dW4ZRnByLA6ZBcCQ== To: Linus Torvalds In-Reply-To: <87mu1lc5mp.fsf@nanos.tec.linutronix.de> References: <20200919091751.011116649@linutronix.de> <87mu1lc5mp.fsf@nanos.tec.linutronix.de> Date: Sun, 20 Sep 2020 10:49:21 +0200 Message-ID: <87k0wode9a.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Subject: Re: [Intel-gfx] [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juri Lelli , Peter Zijlstra , Benjamin Herrenschmidt , Sebastian Andrzej Siewior , dri-devel , linux-mips@vger.kernel.org, Ben Segall , Max Filippov , Guo Ren , linux-sparc , Vincent Chen , Will Deacon , Ard Biesheuvel , linux-arch , Herbert Xu , Michael Ellerman , the arch/x86 maintainers , Russell King , linux-csky@vger.kernel.org, David Airlie , Mel Gorman , "open list:SYNOPSYS ARC ARCHITECTURE" , linux-xtensa@linux-xtensa.org, Paul McKenney , intel-gfx , linuxppc-dev , Steven Rostedt , Dietmar Eggemann , Linux ARM , Chris Zankel , Michal Simek , Thomas Bogendoerfer , Nick Hu , Linux-MM , Vineet Gupta , LKML , Arnd Bergmann , Paul Mackerras , Andrew Morton , Daniel Bristot de Oliveira , "David S. Miller" , Greentime Hu Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Sun, Sep 20 2020 at 08:41, Thomas Gleixner wrote: > On Sat, Sep 19 2020 at 10:18, Linus Torvalds wrote: >> Maybe I've missed something. Is it because the new interface still >> does "pagefault_disable()" perhaps? >> >> But does it even need the pagefault_disable() at all? Yes, the >> *atomic* one obviously needed it. But why does this new one need to >> disable page faults? > > It disables pagefaults because it can be called from atomic and > non-atomic context. That was the point to get rid of > > if (preeemptible()) > kmap(); > else > kmap_atomic(); > > If it does not disable pagefaults, then it's just a lightweight variant > of kmap() for short lived mappings. Actually most usage sites of kmap atomic do not need page faults to be disabled at all. As Daniel pointed out the implicit pagefault disable enforces copy_from_user_inatomic() even in places which are clearly preemptible task context. As we need to look at each instance anyway we can add the PF disable explicitely to the very few places which actually need it. Thanks, tglx _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx