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

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Message-ID: <a6288e81-76de-956a-77e9-bccbcbba366f@linux.intel.com>
Date:   Tue, 25 Aug 2020 11:13:06 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Chris Wilson <chris@...is-wilson.co.uk>,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>
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

Hi Chris,

On 8/24/20 4:35 PM, Chris Wilson wrote:
> 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.

It's caused by left switching 36 bits operation against a 32-bit
integer. Your patch fixes this by converting the integer from unsigned
long to u64. It looks good to me. Thanks!

> -Chris
> 

Best regards,
baolu