From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751374AbeECWw5 (ORCPT ); Thu, 3 May 2018 18:52:57 -0400 Received: from mail.kernel.org ([198.145.29.99]:45450 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751111AbeECWw4 (ORCPT ); Thu, 3 May 2018 18:52:56 -0400 Date: Thu, 3 May 2018 17:52:54 -0500 From: Bjorn Helgaas To: Sinan Kaya Cc: Joerg Roedel , Gil Kupfer , dwmw2@infradead.org, bhelgaas@google.com, iommu@lists.linux-foundation.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, nadav.amit@gmail.com, Gil Kupfer , Will Deacon Subject: Re: [RFC/RFT] Add noats flag to boot parameters Message-ID: <20180503225254.GC15790@bhelgaas-glaptop.roam.corp.google.com> References: <1525025808-2365-1-git-send-email-gilkup@cs.technion.ac.il> <20180503133459.waawna3ebtu3udn6@8bytes.org> <359d736a-a7ac-f0e4-f4db-dc7bb506481c@codeaurora.org> <20180503135920.o2rdh3exai7qmkvu@8bytes.org> <5cf699f1-90c1-5ad8-07fe-a65042395d05@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5cf699f1-90c1-5ad8-07fe-a65042395d05@codeaurora.org> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 03, 2018 at 10:23:02AM -0400, Sinan Kaya wrote: > +Bjorn, > > On 5/3/2018 9:59 AM, Joerg Roedel wrote: > > On Thu, May 03, 2018 at 09:46:34AM -0400, Sinan Kaya wrote: > >> I also like the idea in general. > >> Minor nit.. > >> > >> Shouldn't this be an iommu parameter rather than a PCI kernel command line parameter? > >> We now have an iommu.passthrough argument that prevents page translation. > >> > >> Doesn't this fit into the same category especially when it is the IOMMU drivers that > >> call ATS functions for enablement not the PCI drivers. > > > > ATS is a bit of a grey area between PCI and IOMMU, but since ATS is > > PCI-specific and the code to enable/disable it is in PCI as well, I > > think the parameter makes sense for PCI too. > > OK. Bjorn was interested in having a command line driven feature enables > in driver/pci directory with bitmasks for each optional PCI spec > capability rather than noXYZ feature. It's true that I try to avoid adding *any* kernel parameters as much as possible because they're usually not practical for end-users. I think it's unreasonable to expect users to use "pci=" parameters based on what specific hardware they have. That's too hard to discover and too hard to use. I did wonder about a "pci=safe" parameter that would disable potentially risky features just as a debugging feature [1]. This ATS case is a security question and the parameter is not something that would have to be used to get certain hardware to work, so I think it's probably reasonable to add. I would maybe expand the documentation so it includes the reason somebody might want it, i.e., to defend against malicious PCIe devices. A parameter using bitmasks could be conceivable for developers but sounds too unwieldy for end-users. [1] https://bugzilla.kernel.org/show_bug.cgi?id=196197#c53