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Message-ID: <6ef6c341-924c-57a6-154e-b804d8b0f2c7@linux.intel.com>
Date:   Fri, 24 Jun 2022 15:56:20 +0800
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Subject: Re: [PATCH v3 1/1] iommu/vt-d: Fix RID2PASID setup/teardown failure
To:     Baolu Lu <baolu.lu@linux.intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        Kevin Tian <kevin.tian@intel.com>,
        Ashok Raj <ashok.raj@intel.com>
Cc:     Chenyi Qiang <chenyi.qiang@intel.com>,
        Liu Yi L <yi.l.liu@intel.com>,
        Jacob jun Pan <jacob.jun.pan@intel.com>,
        iommu@lists.linux-foundation.org, iommu@lists.linux.dev,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
References: <20220623065720.727849-1-baolu.lu@linux.intel.com>
 <eb2257b1-1213-1001-74bd-085af5d50dad@linux.intel.com>
 <b8a7ab77-935d-459c-7f65-628fcf828fad@linux.intel.com>
From:   Ethan Zhao <haifeng.zhao@linux.intel.com>
In-Reply-To: <b8a7ab77-935d-459c-7f65-628fcf828fad@linux.intel.com>
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在 2022/6/24 14:54, Baolu Lu 写道:
> On 2022/6/24 14:02, Ethan Zhao wrote:
>> 在 2022/6/23 14:57, Lu Baolu 写道:
>>> The IOMMU driver shares the pasid table for PCI alias devices. When the
>>> RID2PASID entry of the shared pasid table has been filled by the first
>>> device, the subsequent device will encounter the "DMAR: Setup RID2PASID
>>> failed" failure as the pasid entry has already been marked as present.
>>> As the result, the IOMMU probing process will be aborted.
>>>
>>> On the contrary, when any alias device is hot-removed from the system,
>>> for example, by writing to /sys/bus/pci/devices/.../remove, the shared
>>> RID2PASID will be cleared without any notifications to other devices.
>>> As the result, any DMAs from those rest devices are blocked.
>>>
>>> Sharing pasid table among PCI alias devices could save two memory pages
>>> for devices underneath the PCIe-to-PCI bridges. Anyway, considering 
>>> that
>>> those devices are rare on modern platforms that support VT-d in 
>>> scalable
>>> mode and the saved memory is negligible, it's reasonable to remove this
>>> part of immature code to make the driver feasible and stable.
>> In my understanding, thus cleanning will make the pasid table become
>> per-dev datastructure whatever the dev is pci-alias or not, and the
>> pasid_pte_is_present(pte)will only check against every pci-alias' own
>> private pasid table,the setup stagewouldn't break, so does the
>> detach/release path, and little value to code otherreference counter
>> like complex implenmataion, looks good to me !
>
> Thanks! Can I add a Reviewd-by from you?
Sure !
>
> Best regards,
> baolu

-- 
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