linux-kernel - Re: [RESEND PATCH v3] iommu/vt-d: Use passthrough mode for the Intel IPUs

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Message-ID: <d9d8fba9-a53a-11ea-9b28-ee5695da48eb@linux.intel.com>
Date:   Thu, 5 Jan 2023 18:49:09 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     bingbu.cao@...el.com, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, iommu@...ts.linux.dev
Cc:     baolu.lu@...ux.intel.com, senozhatsky@...omium.org,
        bingbu.cao@...ux.intel.com, sangram.k.y@...el.com
Subject: Re: [RESEND PATCH v3] iommu/vt-d: Use passthrough mode for the Intel
 IPUs

On 2023/1/5 16:28, bingbu.cao@...el.com wrote:
> Intel IPU(Image Processing Unit) has its own (IO)MMU hardware,
> The IPU driver allocates its own page table that is not mapped
> via the DMA, and thus the Intel IOMMU driver blocks access giving
> this error:
> 
> DMAR: DRHD: handling fault status reg 3
> DMAR: [DMA Read] Request device [00:05.0] PASID ffffffff
>        fault addr 76406000 [fault reason 06] PTE Read access is not set

Do you mind telling why does such DMA fault occur? How does the IPU
driver map the fault address 76406000 ?

> As IPU is not an external facing device which is not risky, so use
> IOMMU passthrough mode for Intel IPUs.

You can also set the passthrough mode with kernel option iommu=pt
(globally) or by writing IDENTITY to

/sys/..path_to_device../iommu_group/type

(per-device).

> Fixes: 26f5689592e2 ("media: staging/intel-ipu3: mmu: Implement driver")

Please don't try to fix any problem in the device driver by adding any
hard-coded quirky code in the IOMMU code.

> Signed-off-by: Bingbu Cao<bingbu.cao@...el.com>

--
Best regards,
baolu