linux-kernel - RE: [PATCH v2 4/6] iommu/vt-d: Remove 1:1 mappings from identity domain

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <BN9PR11MB5276614392E99F75B6A592C68C8DA@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Wed, 13 Dec 2023 02:20:10 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "Will Deacon" <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "Jason Gunthorpe" <jgg@...pe.ca>
CC:     "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 4/6] iommu/vt-d: Remove 1:1 mappings from identity
 domain

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Tuesday, December 12, 2023 2:21 PM
> >
> > For GFX it's a workaround added since day one. there is even still
> > an option CONFIG_INTEL_IOMMU_BROKEN_GFX_WA available. But
> > now its meaning is really disabling IOMMU instead of using identity.
> >
> > sounds like IDENTMAP_GFX can be fully removed now:
> >
> > #ifdef CONFIG_INTEL_IOMMU_BROKEN_GFX_WA
> > 	dmar_map_gfx = 0;
> > #endif
> 
> We should already remove the workaround for the 2.6 kernel. :-)

I don't know what happened to ignore that temporary option.

> 
> It's default "n". Therefore, if any gfx driver still needs this
> workaround, there should already be a bug report.

It depends on how it is set in distros.

> 
> >
> > 	if (!dmar_map_gfx)
> > 		iommu_identity_mapping |= IDENTMAP_GFX;
> 
> So with above cleaned up, we have no need to worry about drivers that
> are not capable of handling remapped dma address any more.
> 
> Did I miss anything?

I prefer to removing IDENTMAP_GFX in this series and put a comment
explaining why Azalia device has no problem.

Then send a separate patch to remove the GFX workaround option.
If there is any valid usage still relying on that, it's easy to revert.