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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 0F8C9CA9ECB for ; Thu, 31 Oct 2019 15:42:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D537B2086D for ; Thu, 31 Oct 2019 15:42:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572536577; bh=GRreUt5vILq8iwJLnTWSsnpWtfLL+f+wCy2zYdNxf6o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=Q1aJKquVchuU9hc9d3fwceUAdP9OcWQ9DkzfSC9eYy58MMPBn0tis2xkBnzzpbWo5 sZE8tpneleer19tR3a1+3n8ylc/WhDNZyuY+v38ZnH7IMI/rQb7PGcGE7bgn0vMMTm lO452WZpTl6tT2OEnfsIfh6k3S0DRHuYtEw+kICc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728446AbfJaPm4 (ORCPT ); Thu, 31 Oct 2019 11:42:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:50140 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727579AbfJaPmw (ORCPT ); Thu, 31 Oct 2019 11:42:52 -0400 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 DECD82086D; Thu, 31 Oct 2019 15:42:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572536572; bh=GRreUt5vILq8iwJLnTWSsnpWtfLL+f+wCy2zYdNxf6o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qaAJ8XcWGfT4LUOvU811aRsvOWAxezJATr7Uk9nzN23oXUvKxtHZVcY0AqzVTOyjZ Epk2/3n2IWDhuOaWcOoDQDWApaqgYgldCxMrpckQEgKjPXnL2Tv96+pJVdwc1WPwcm ftKHIyiFmV9Fi/cSBRpiXvhFrSLJm+8Fm2Mkj3Fg= Date: Thu, 31 Oct 2019 15:42:47 +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: <20191031154247.GB28061@willie-the-truck> References: <20191030145112.19738-1-will@kernel.org> <20191030145112.19738-6-will@kernel.org> <20191030193148.GA8432@8bytes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191030193148.GA8432@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 Wed, Oct 30, 2019 at 08:31:48PM +0100, Joerg Roedel wrote: > On Wed, Oct 30, 2019 at 02:51:10PM +0000, Will Deacon wrote: > > By removing the redundant call to 'pci_request_acs()' we can allow the > > ARM SMMUv3 driver to be built as a module. > > > > Signed-off-by: Will Deacon > > --- > > drivers/iommu/Kconfig | 2 +- > > drivers/iommu/arm-smmu-v3.c | 1 - > > 2 files changed, 1 insertion(+), 2 deletions(-) > > > > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig > > index e3842eabcfdd..7583d47fc4d5 100644 > > --- a/drivers/iommu/Kconfig > > +++ b/drivers/iommu/Kconfig > > @@ -388,7 +388,7 @@ config ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT > > config. > > > > config ARM_SMMU_V3 > > - bool "ARM Ltd. System MMU Version 3 (SMMUv3) Support" > > + tristate "ARM Ltd. System MMU Version 3 (SMMUv3) Support" > > depends on ARM64 > > select IOMMU_API > > select IOMMU_IO_PGTABLE_LPAEa > > Sorry for the stupid question, but what prevents the iommu module from > being unloaded when there are active users? There are no symbol > dependencies to endpoint device drivers, because the interface is only > exposed through the iommu-api, right? Is some sort of manual module > reference counting needed? 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. Will