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=-3.8 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 D5E75C55179 for ; Mon, 2 Nov 2020 16:42:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8E2F2223AC for ; Mon, 2 Nov 2020 16:42:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="DejrOT1E" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726886AbgKBQme (ORCPT ); Mon, 2 Nov 2020 11:42:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41486 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727332AbgKBQmd (ORCPT ); Mon, 2 Nov 2020 11:42:33 -0500 Received: from mail-ot1-x341.google.com (mail-ot1-x341.google.com [IPv6:2607:f8b0:4864:20::341]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E36B9C061A47 for ; Mon, 2 Nov 2020 08:42:32 -0800 (PST) Received: by mail-ot1-x341.google.com with SMTP id n11so13195963ota.2 for ; Mon, 02 Nov 2020 08:42:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=LkcPNNpMLX6kEqUed20/jhdzhJZXy+qPlqOir1Z4UWg=; b=DejrOT1ET977KzMedOZFf/nvESeZd35VW615DHzfUVNv/jtr5S39tQRR1rkXRrNQsS 8e7QakA0NQZajazNYknFTyPn7wzCTD0MaLh6LD79vAKy5J2WjkyqZwU1hUMlTMpcVTcY aRcqJL/19jZSjJmXa+xeFfRoO2oW4s/0IBZV8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=LkcPNNpMLX6kEqUed20/jhdzhJZXy+qPlqOir1Z4UWg=; b=JJ1eSY0ngR5jkBS2o3E+5uk5/h7sekmsSc330Rkppk03cKFCcPe3A5c/xW+VNxjU2l JHo307fn+ilD91OnhZlKKJCqii1TREHI/sJP0xuv4yt4h9NJWYEHH61xeOQFClNj5FfL FEcZorY61ht47wbC86AILdkUqOc+LI5XljdfGig0kB8lhugs4FsuxX/uFuXBQKQsmgTM bCnY4p4SS8mF1QdmCNnCvVArkssGN9x70tLVS1gjFu14i2Ty62Vw5c/fb8zMpgrYld1S 7Z3NIlS53aFxZAdqhJMdjQlAiRwv1To47jPkb35o6fz9iTE7iWH6d879tpaDDHSPxQTj H/hQ== X-Gm-Message-State: AOAM532EVJ/mcUdEMsRiAKoGqsZ/LfEqnfL51NYe1PnXtycNAtsc5xJX yIv4aRWJ6BQKo/eRUAxfhTeBph9SsPOvK/VqV5Ie1Q== X-Google-Smtp-Source: ABdhPJw6fgeaE8WrMv6/yjTLi0nLsEgIsTJGq7lnieyfjRKsxeZQjFjVvPlXPA1vJ6n1s7o3wIRvF8cXTGM5e/OE7rM= X-Received: by 2002:a05:6830:1647:: with SMTP id h7mr13325941otr.281.1604335352341; Mon, 02 Nov 2020 08:42:32 -0800 (PST) MIME-Version: 1.0 References: <20201030100815.2269-1-daniel.vetter@ffwll.ch> <20201030100815.2269-9-daniel.vetter@ffwll.ch> <20201102072931.GA16419@infradead.org> <20201102130115.GC36674@ziepe.ca> <20201102155256.GG36674@ziepe.ca> In-Reply-To: <20201102155256.GG36674@ziepe.ca> From: Daniel Vetter Date: Mon, 2 Nov 2020 17:42:20 +0100 Message-ID: Subject: Re: [PATCH v5 08/15] mm: Add unsafe_follow_pfn To: Jason Gunthorpe Cc: Christoph Hellwig , DRI Development , LKML , KVM list , Linux MM , Linux ARM , linux-samsung-soc , "open list:DMA BUFFER SHARING FRAMEWORK" , Daniel Vetter , Kees Cook , Dan Williams , Andrew Morton , John Hubbard , "J??r??me Glisse" , Jan Kara Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-samsung-soc@vger.kernel.org On Mon, Nov 2, 2020 at 4:52 PM Jason Gunthorpe wrote: > > On Mon, Nov 02, 2020 at 02:23:58PM +0100, Daniel Vetter wrote: > > On Mon, Nov 2, 2020 at 2:01 PM Jason Gunthorpe wrote: > > > > > > On Mon, Nov 02, 2020 at 01:56:10PM +0100, Daniel Vetter wrote: > > > > On Mon, Nov 2, 2020 at 8:29 AM Christoph Hellwig wrote: > > > > > > > > > > On Fri, Oct 30, 2020 at 11:08:08AM +0100, Daniel Vetter wrote: > > > > > > Also mark up follow_pfn as EXPORT_SYMBOL_GPL. The only safe way to use > > > > > > that by drivers/modules is together with an mmu_notifier, and that's > > > > > > all _GPL stuff. > > > > > > > > > > I also think it also needs to be renamed to explicitly break any existing > > > > > users out of tree or int the submission queue. > > > > > > > > Ok I looked at the mmu notifier locking again and noticed that > > > > mm->subscriptions has its own spinlock. Since there usually shouldn't > > > > be a huge pile of these I think it's feasible to check for the mmu > > > > notifier in follow_pfn. And that would stuff this gap for good. I'll > > > > throw that on top as a final patch and see what people think. > > > > > > Probably the simplest is to just check mm_has_notifiers() when in > > > lockdep or something very simple like that > > > > lockdep feels wrong, was locking more at CONFIG_DEBUG_VM. And since > > generally you only have 1 mmu notifier (especially for kvm) I think we > > can also pay the 2nd cacheline miss and actually check the right mmu > > notifier is registered. > > Need to hold the lock to check that and there are two ways to register > notifiers these days, so it feels to expensive to me. Uh I mixed stuff up all along, struct mmu_notifier *subcription that all the mmu notifier users use has the ->mm pointer we want right there. That's good enough I think. Now I'm kinda lost in kvm code trying to wire it through, but it's looking ok-ish thus far :-) -Daniel > CH's 'export symbol only for kvm' really does seem the most robust way > to handle this though. > > Jason -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch