linux-kernel - Re: [PATCH v7 4/4] PCI: Introduce the disable_acs

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Message-ID: <a3197c27-1b41-7784-374b-948e43471789@deltatee.com>
Date:   Tue, 17 Jul 2018 11:49:22 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-doc@...r.kernel.org, Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christian König <christian.koenig@....com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v7 4/4] PCI: Introduce the disable_acs_redir parameter



On 17/07/18 11:48 AM, Alex Williamson wrote:
> On Tue, 17 Jul 2018 11:02:04 -0600
> Logan Gunthorpe <logang@...tatee.com> wrote:
> 
>> In order to support P2P traffic on a segment of the PCI hierarchy,
>> we must be able to disable the ACS redirect bits for select
>> PCI bridges. The bridges must be selected before the devices are
>> discovered by the kernel and the IOMMU groups created. Therefore,
>> a kernel command line parameter is created to specify devices
>> which must have their ACS bits disabled.
>>
>> The new parameter takes a list of devices separated by a semicolon.
>> Each device specified will have it's ACS redirect bits disabled.
>> This is similar to the existing 'resource_alignment' parameter.
>>
>> The ACS Request P2P Request Redirect, P2P Completion Redirect and P2P
>> Egress Control bits are disabled which is sufficient to always allow
>> passing P2P traffic uninterrupted. The bits are set after the kernel
>> (optionally) enables the ACS bits itself. It is also done regardless of
>> whether the kernel sets the bits or not seeing some BIOS firmware is known
>> to set the bits on boot.
>>
>> If the user tries to disable the ACS redirct for a device without the
>> ACS capability, a warning is printed to dmesg.
>>
>> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
>> Reviewed-by: Stephen Bates <sbates@...thlin.com>
>> Acked-by: Christian König <christian.koenig@....com>
>> ---
>>  Documentation/admin-guide/kernel-parameters.txt |  9 +++
>>  drivers/pci/pci.c                               | 76 ++++++++++++++++++++++++-
>>  2 files changed, 83 insertions(+), 2 deletions(-)
> 
> Thanks for the re-spins!
> 
> Reviewed-by: Alex Williamson <alex.williamson@...hat.com>


Thanks for all the thorough review!

Logan