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From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     Lu Baolu <baolu.lu@linux.intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        "Raj, Ashok" <ashok.raj@intel.com>
CC:     "Qiang, Chenyi" <chenyi.qiang@intel.com>,
        Ethan Zhao <haifeng.zhao@linux.intel.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        "Pan, Jacob jun" <jacob.jun.pan@intel.com>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH v3 1/1] iommu/vt-d: Fix RID2PASID setup/teardown failure
Thread-Topic: [PATCH v3 1/1] iommu/vt-d: Fix RID2PASID setup/teardown failure
Thread-Index: AQHYhs8ZnDJgEPiUSU6v0m07+WgrOK1eGi/g
Date:   Fri, 24 Jun 2022 06:31:45 +0000
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References: <20220623065720.727849-1-baolu.lu@linux.intel.com>
In-Reply-To: <20220623065720.727849-1-baolu.lu@linux.intel.com>
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> From: Lu Baolu <baolu.lu@linux.intel.com>
> Sent: Thursday, June 23, 2022 2:57 PM
>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> Fixes: ef848b7e5a6a0 ("iommu/vt-d: Setup pasid entry for RID2PASID
> support")
> Reported-by: Chenyi Qiang <chenyi.qiang@intel.com>
> Reported-by: Ethan Zhao <haifeng.zhao@linux.intel.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>

Looks good.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>