linux-kernel - RE: [PATCH 1/1] iommu/vt-d: Add opt-in for ATS support on discrete devices

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Date:   Tue, 7 Mar 2023 05:20:07 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     Robin Murphy <robin.murphy@....com>,
        Baolu Lu <baolu.lu@...ux.intel.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/1] iommu/vt-d: Add opt-in for ATS support on discrete
 devices

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Friday, March 3, 2023 9:18 PM
> 
> On Fri, Mar 03, 2023 at 08:19:29AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@...dia.com>
> > > Sent: Thursday, March 2, 2023 1:43 AM
> > >
> > > If Intel BIOS's have populated the "satcu" to say that ATS is not
> > > supported by the HW when the HW supports ATS perfectly fine, then get
> > > the BIOS fixed or patch the ACPI until it is fixed. The BIOS should
> > > not be saying that the HW does not support ATS when it does, it is a
> > > simple BIOS bug.
> > >
> >
> > That is not the purpose of SATC.
> >
> > The ATS support in VT-d side is reported in two interfaces:
> >
> > 1) "Device-TLB support" in Extended Capability Register;
> > 2) Root port ATS capability in ACPI ATSR structure;
> >
> > A device gets ATS enabled if 1/2 are true and !pdev->untrusted. Same
> > as SMMU does.
> >
> > The main purpose of SATC is to describe which ATS-capable integrated
> > device meets the requirements of securely using ATS as stated in VT-d
> > spec 4.4.
> 
> Then it should be mapped to pdev->untrusted and possibly
> pdev->untrusted to be enhanced to be more descriptive.
> 
> iommu driver and BIOS should have no role in security policy beyond
> feeding in data to a common policy engine.
> 

That makes sense.