linux-kernel - RE: [PATCH v3 1/1] iommu/vt-d: Fix RID2PASID setup/teardown failure

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Message-ID: <BN9PR11MB5276A576BABC8E9525966E388CB49@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Fri, 24 Jun 2022 06:31:45 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "Raj, Ashok" <ashok.raj@...el.com>
CC:     "Qiang, Chenyi" <chenyi.qiang@...el.com>,
        Ethan Zhao <haifeng.zhao@...ux.intel.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH v3 1/1] iommu/vt-d: Fix RID2PASID setup/teardown failure

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Thursday, June 23, 2022 2:57 PM
> 
> 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.
> 
> Fixes: ef848b7e5a6a0 ("iommu/vt-d: Setup pasid entry for RID2PASID
> support")
> Reported-by: Chenyi Qiang <chenyi.qiang@...el.com>
> Reported-by: Ethan Zhao <haifeng.zhao@...ux.intel.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>

Looks good.

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