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=-3.5 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 37B5EC4363A for ; Fri, 30 Oct 2020 13:13:29 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 3C86120731 for ; Fri, 30 Oct 2020 13:13:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="JKDGOHNW" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3C86120731 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4CN2mz0jPBzDqf3 for ; Sat, 31 Oct 2020 00:13:23 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=infradead.org (client-ip=2001:8b0:10b:1236::1; helo=casper.infradead.org; envelope-from=willy@infradead.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=infradead.org Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) (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 4CN2gT4YSVzDqmq for ; Sat, 31 Oct 2020 00:08:37 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=rfcpHo3sYbHG9663+/oEKU5+yDacWVNSfCtmxqY30IA=; b=JKDGOHNWU/V8Y+2rs/k7xDcd+D ywFaOKdh66CG7CRxohaMqHaFLXYS9D8UEmY4cTPadxISCv3CHKX+79wCldI0LV8nLjJimNpRjUFot BbcFgkfMoOoVVqbSn6at/tUwkE3W4TeiBSkn85uGjZxEhlxcEUEn86bKSTG6W3x+/e6w76iTiIDMo +S7YG45wv9UKO0gFrKbYfO0n5SfTbF1pG2kSlc2FKZXNaKU1XoICbQHjohPVjgTGHFNPIe1Xmtc6u jm1U+Hxe5+XhivRe6Qrj/AgJuMiGDjrS/uMW8LgIirsxF3LkwsBxbZgQIkCutkdRTk0XP+Op+X95w kA9B9H+g==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kYU6t-0002Yw-HM; Fri, 30 Oct 2020 13:06:27 +0000 Date: Fri, 30 Oct 2020 13:06:27 +0000 From: Matthew Wilcox To: Thomas Gleixner Subject: Re: [patch V2 00/18] mm/highmem: Preemptible variant of kmap_atomic & friends Message-ID: <20201030130627.GI27442@casper.infradead.org> References: <20201029221806.189523375@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201029221806.189523375@linutronix.de> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juri Lelli , linux-xtensa@linux-xtensa.org, Peter Zijlstra , Sebastian Andrzej Siewior , linux-mips@vger.kernel.org, Ben Segall , linux-mm@kvack.org, Guo Ren , sparclinux@vger.kernel.org, Vincent Chen , Ingo Molnar , linux-arch@vger.kernel.org, Vincent Guittot , Herbert Xu , x86@kernel.org, Russell King , linux-csky@vger.kernel.org, Christoph Hellwig , David Airlie , Mel Gorman , linux-snps-arc@lists.infradead.org, Ard Biesheuvel , Paul McKenney , linuxppc-dev@lists.ozlabs.org, Steven Rostedt , Linus Torvalds , Greentime Hu , Dietmar Eggemann , linux-arm-kernel@lists.infradead.org, Chris Zankel , Michal Simek , Thomas Bogendoerfer , Nick Hu , Max Filippov , Vineet Gupta , LKML , Arnd Bergmann , Daniel Vetter , Paul Mackerras , Andrew Morton , Daniel Bristot de Oliveira , "David S. Miller" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Oct 29, 2020 at 11:18:06PM +0100, Thomas Gleixner wrote: > This series provides kmap_local.* iomap_local variants which only disable > migration to keep the virtual mapping address stable accross preemption, > but do neither disable pagefaults nor preemption. The new functions can be > used in any context, but if used in atomic context the caller has to take > care of eventually disabling pagefaults. Could I ask for a CONFIG_KMAP_DEBUG which aliases all the kmap variants to vmap()? I think we currently have a problem in iov_iter on HIGHMEM configs: copy_page_to_iter() calls page_copy_sane() which checks: head = compound_head(page); if (likely(n <= v && v <= page_size(head))) return true; but then: void *kaddr = kmap_atomic(page); size_t wanted = copy_to_iter(kaddr + offset, bytes, i); kunmap_atomic(kaddr); so if offset to offset+bytes is larger than PAGE_SIZE, this is going to work for lowmem pages and fail miserably for highmem pages. I suggest vmap() because vmap has a PAGE_SIZE gap between each allocation. Alternatively if we could have a kmap_atomic_compound(), that would be awesome, but probably not realistic to implement. I've more or less resigned myself to having to map things one page at a time.