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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 03DFEC5DF60 for ; Fri, 8 Nov 2019 11:03:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C501D21924 for ; Fri, 8 Nov 2019 11:03:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573210996; bh=J/Gsm5N/mj+ik5tmWzF15ve/593DRKXBLK4N9zKCikI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=oa5w4zCicV2OgE2bdl6n+8aSVCzDrXbvqe57H8szaftSxT9fyYO+T37aO1iBbs0G1 FBNrRln2s41P0Z0lK5lSjG/yEUOgY+F57EHVVnQjUBxkjwPJKMQXM6LRHBY7bCzXIW GmwQyp6PZlVToPA7OxGmaDLRWuodfx/2d7CEKC1o= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731752AbfKHLDP (ORCPT ); Fri, 8 Nov 2019 06:03:15 -0500 Received: from mail.kernel.org ([198.145.29.99]:39474 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726149AbfKHLDP (ORCPT ); Fri, 8 Nov 2019 06:03:15 -0500 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C72EF206BA; Fri, 8 Nov 2019 11:03:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573210994; bh=J/Gsm5N/mj+ik5tmWzF15ve/593DRKXBLK4N9zKCikI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=GPUpB2qieVF3EyX+Obw28FlE6xo23nwE/xykonNN3EZtnaxcpvEFeX+8ufsaXb5th +ksXQteLE30PzN2sUWXuJdcrvuV/YqSRLbHtKk9h1qsPcUG586CeeZJJMYvyQclJah tyoRDGyrsSCcnNRNjplrIRLCVouz6GYQbwN+T1LQ= Date: Fri, 8 Nov 2019 11:03:10 +0000 From: Will Deacon To: Joerg Roedel Cc: iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Robin Murphy , Bjorn Helgaas , Lorenzo Pieralisi Subject: Re: [PATCH 5/7] iommu/arm-smmu-v3: Allow building as a module Message-ID: <20191108110310.GC19153@willie-the-truck> References: <20191030145112.19738-1-will@kernel.org> <20191030145112.19738-6-will@kernel.org> <20191030193148.GA8432@8bytes.org> <20191031154247.GB28061@willie-the-truck> <20191105121508.GA3479@8bytes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191105121508.GA3479@8bytes.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Joerg, On Tue, Nov 05, 2019 at 01:15:08PM +0100, Joerg Roedel wrote: > On Thu, Oct 31, 2019 at 03:42:47PM +0000, Will Deacon wrote: > > Generally, I think unloading the IOMMU driver module while there are > > active users is a pretty bad idea, much like unbinding the driver via > > /sys in the same situation would also be fairly daft. However, I *think* > > the code in __device_release_driver() tries to deal with this by > > iterating over the active consumers and ->remove()ing them first. > > > > I'm without hardware access at the moment, so I haven't been able to > > test this myself. We could nobble the module_exit() hook, but there's > > still the "force unload" option depending on the .config. > > Okay, but besides the force-unload case, can we prevent accidential > unloading by taking a reference to the module in add_device() and release > it in remove_device()? That's probably a sensible starting point, yes. In conjunction with the patch from Jean-Philippe to introduce bus_unset_iommu(), we might have a fighting chance of getting this to work. I'll spin a v2. Thanks! Will