linux-kernel - Re: [PATCH RFCv1 1/3] PCI: Allow ATS to be always on for CXL.cache capable devices

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Message-ID: <aXJQVprkiMCWxDyp@Asurada-Nvidia>
Date: Thu, 22 Jan 2026 08:29:10 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <dan.j.williams@...el.com>, Jonathan Cameron
	<jonathan.cameron@...wei.com>, "Tian, Kevin" <kevin.tian@...el.com>,
	"will@...nel.org" <will@...nel.org>, "robin.murphy@....com"
	<robin.murphy@....com>, "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"joro@...tes.org" <joro@...tes.org>, "praan@...gle.com" <praan@...gle.com>,
	"baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
	"miko.lenczewski@....com" <miko.lenczewski@....com>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-pci@...r.kernel.org"
	<linux-pci@...r.kernel.org>, <linux-cxl@...r.kernel.org>
Subject: Re: [PATCH RFCv1 1/3] PCI: Allow ATS to be always on for CXL.cache
 capable devices

On Thu, Jan 22, 2026 at 09:14:32AM -0400, Jason Gunthorpe wrote:
> On Wed, Jan 21, 2026 at 09:44:32PM -0800, dan.j.williams@...el.com wrote:
> > "We have a less than perfect legacy way (PCI untrusted flag) to nod at
> >  ATS security problems. Let us ignore even that for a new class of
> >  devices that advertise they can trigger all the old security problems
> >  plus new ones."
> 
> Ah, I missed that we are already force disabling ATS in this untrusted
> case, so we should ensure that continues to be the case here
> too. Nicolin does it need a change?

pci_ats_always_on() validates against !pci_ats_supported(pdev), so
we ensured that untrusted devices would not be always on.

Perhaps we should highlight in the commit message, as it's a topic?

Nicolin