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,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 8613FC4742C for ; Mon, 2 Nov 2020 16:42:35 +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 A582B222B9 for ; Mon, 2 Nov 2020 16:42:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="DejrOT1E" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A582B222B9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ffwll.ch Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id BEECC6E47B; Mon, 2 Nov 2020 16:42:33 +0000 (UTC) Received: from mail-ot1-x342.google.com (mail-ot1-x342.google.com [IPv6:2607:f8b0:4864:20::342]) by gabe.freedesktop.org (Postfix) with ESMTPS id F09FD6E47B for ; Mon, 2 Nov 2020 16:42:32 +0000 (UTC) Received: by mail-ot1-x342.google.com with SMTP id j14so2969702ots.1 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=DOdjvr/rIEQoOkk3QfKAZuhlIQPOf5DRLCqGwgEbr6pbJ8eBBueE8BT8c2M5738IEC TKzanrFFVhfVCXhlacODkKA7IElROs6OTVsphAYBb7Cm7Ux6hqmactaEoztDpJubdE5u 5j33IHF+h/74JW+ZW2dsYfQRfSsqiK/AJiHVTyFcfhIgln06++B0206fm+19D3r1uIrf coNRi26zC3jinDwGQyfFxjc3yMhlH3lO4c5PVKCuGFrqHGLvOlxFLydgVNXSPfyGdlw1 W4NZpidWjpk2vG8jgS27PYKaHeHPQN8mtOEOytDP2auQ5H8JI1Qw87ybOBspEYowdHnV wp7A== X-Gm-Message-State: AOAM530+UMn+24ee6cznP7cxedguY1TDbDx+i5moBWnhY+VVgmwHsc6c T3mwcV0vwQQL7vhQHuHABSM0zg7zwuSh5kj82DzVxg== 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 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-samsung-soc , Jan Kara , Kees Cook , KVM list , John Hubbard , LKML , DRI Development , Christoph Hellwig , Linux MM , J??r??me Glisse , Daniel Vetter , Dan Williams , Andrew Morton , Linux ARM , "open list:DMA BUFFER SHARING FRAMEWORK" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" 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 _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel