linux-kernel - Re: [PATCH v4 07/15] iommu/vt-d: Delegate the dma domain to upper layer

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Message-ID: <159825811140.30134.5347490249201789397@build.alporthouse.com>
Date:   Mon, 24 Aug 2020 09:35:11 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     baolu.lu@...ux.intel.com, ashok.raj@...el.com,
        jacob.jun.pan@...el.com, kevin.tian@...el.com,
        jamessewart@...sta.com, tmurphy@...sta.com, dima@...sta.com,
        sai.praneeth.prakhya@...el.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 07/15] iommu/vt-d: Delegate the dma domain to upper layer

Quoting Lu Baolu (2020-08-24 07:31:23)
> Hi Chris,
> 
> On 2020/8/22 2:33, Chris Wilson wrote:
> > Quoting Lu Baolu (2019-05-25 06:41:28)
> >> This allows the iommu generic layer to allocate a dma domain and
> >> attach it to a device through the iommu api's. With all types of
> >> domains being delegated to upper layer, we can remove an internal
> >> flag which was used to distinguish domains mananged internally or
> >> externally.
> > 
> > I'm seeing some really strange behaviour with this patch on a 32b
> > Skylake system (and still present on mainline). Before this patch
> > everything is peaceful and appears to work correctly. Applying this patch,
> > and we fail to initialise the GPU with a few DMAR errors reported, e.g.
> > 
> > [   20.279445] DMAR: DRHD: handling fault status reg 3
> > [   20.279508] DMAR: [DMA Read] Request device [00:02.0] fault addr 8900a000 [fault reason 05] PTE Write access is not set
> > 
> > Setting an identity map for the igfx made the DMAR errors disappear, but
> > the GPU still failed to initialise.
> > 
> > There's no difference in the DMAR configuration dmesg between working and
> > the upset patch. And the really strange part is that switching to a 64b
> > kernel with this patch, it's working.
> > 
> > Any suggestions on what I should look for?
> 
> Can the patch titled "[PATCH] iommu/intel: Handle 36b addressing for
> x86-32" solve this problem?

It does. Not sure why, but that mystery I can leave for others.
-Chris