linux-kernel - Re: [PATCH] pci: Add a acs_disable option for pci kernel parameter

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Message-ID: <7AEEED4D-1C64-4330-96E2-AB665E3D4B7D@raithlin.com>
Date:   Mon, 30 Oct 2017 01:04:47 +0000
From:   "Stephen  Bates" <sbates@...thlin.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     "corbet@....net" <corbet@....net>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "cdall@...aro.org" <cdall@...aro.org>,
        "marc.zyngier@....com" <marc.zyngier@....com>,
        "zohar@...ux.vnet.ibm.com" <zohar@...ux.vnet.ibm.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "logang@...tatee.com" <logang@...tatee.com>,
        "tom@...pey.com" <tom@...pey.com>
Subject: Re: [PATCH] pci: Add a acs_disable option for pci kernel parameter

>> This patch adds a new boot option to the pci kernel parameter called
>> "acs_disable" that will disable ACS. This is useful for PCI peer to
>> peer communication but can cause problems when IOVA isolation is
>> required and an IOMMU is enabled. Use with care.

> Eww.

Thanks for the feedback Christoph. My sentiments exactly ;-).  

> Can we please add smbios quirks for the systems where you've
> observed this? 

I can look at doing this. The issue with this approach is that it will require a kernel patch for each new system that is detected.

> we probably also want to keep the option just in case).

Agreed. At least then operators have a path to ACS disable prior to a quirk being accepted.

Stephen