linux-kernel - RE: [RFC PATCH 2/5] iommu/vt-d: Add generic IO page table support

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Message-ID: <MW5PR11MB5881FC3D9DBF14D6BD07025489AFA@MW5PR11MB5881.namprd11.prod.outlook.com>
Date:   Thu, 9 Nov 2023 00:10:59 +0000
From:   "Zhang, Tina" <tina.zhang@...el.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH 2/5] iommu/vt-d: Add generic IO page table support

Hi Jason,

> -----Original Message-----
> From: Jason Gunthorpe <jgg@...pe.ca>
> Sent: Tuesday, November 7, 2023 3:32 AM
> To: Zhang, Tina <tina.zhang@...el.com>
> Cc: Jean-Philippe Brucker <jean-philippe@...aro.org>; Tian, Kevin
> <kevin.tian@...el.com>; Lu Baolu <baolu.lu@...ux.intel.com>; joro@...tes.org;
> will@...nel.org; Liu, Yi L <yi.l.liu@...el.com>; virtualization@...ts.linux-
> foundation.org; iommu@...ts.linux.dev; linux-kernel@...r.kernel.org
> Subject: Re: [RFC PATCH 2/5] iommu/vt-d: Add generic IO page table support
> 
> On Mon, Nov 06, 2023 at 02:12:23AM -0500, Tina Zhang wrote:
> > Add basic hook up code to implement generic IO page table framework.
> >
> > Signed-off-by: Tina Zhang <tina.zhang@...el.com>
> > ---
> >  drivers/iommu/intel/Kconfig |  1 +
> >  drivers/iommu/intel/iommu.c | 94
> > +++++++++++++++++++++++++++++++++++++
> >  drivers/iommu/intel/iommu.h |  7 +++
> >  drivers/iommu/io-pgtable.c  |  3 ++
> >  include/linux/io-pgtable.h  |  2 +
> >  5 files changed, 107 insertions(+)
> 
> If this is going to happen can we also convert vt-d to actually use the io page
> table stuff directly and shuffle the code around so it is structured like the rest of
> the io page table implementations?
Converting VT-d driver to use io page table involves much code change. I made a local version of it, and it didn't prove much benefit.

VT-d only supports one 1st-stage IO pgtable format and one 2nd-stage IO pgtable format. So, the current IO pgtable handling operations seems more efficient comparing to adding another layer callbacks in them.

We have a plan to add a new io_pgtable.c file under VT-d driver directory and use that file to collect IO pgtable related functions. But we want to hold on converting VT-d to use the IO page table directly unless we can see some benefits.

Regards,
-Tina
> 
> Jason