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    Subject[PATCH v4 7/7] iommu/vt-d: Disable multiple GPASID-dev bind
    Date
    For the unlikely use case where multiple aux domains from the same pdev
    are attached to a single guest and then bound to a single process
    (thus same PASID) within that guest, we cannot easily support this case
    by refcounting the number of users. As there is only one SL page table
    per PASID while we have multiple aux domains thus multiple SL page tables
    for the same PASID.

    Extra unbinding guest PASID can happen due to race between normal and
    exception cases. Termination of one aux domain may affect others unless
    we actively track and switch aux domains to ensure the validity of SL
    page tables and TLB states in the shared PASID entry.

    Support for sharing second level PGDs across domains can reduce the
    complexity but this is not available due to the limitations on VFIO
    container architecture. We can revisit this decision once sharing PGDs
    are available.

    Overall, the complexity and potential glitch do not warrant this unlikely
    use case thereby removed by this patch.

    Fixes: 56722a4398a30 ("iommu/vt-d: Add bind guest PASID support")
    Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
    Cc: Kevin Tian <kevin.tian@intel.com>
    Cc: Lu Baolu <baolu.lu@linux.intel.com>
    Reviewed-by: Eric Auger <eric.auger@redhat.com>
    Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
    Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
    ---
    drivers/iommu/intel/svm.c | 22 +++++++++-------------
    1 file changed, 9 insertions(+), 13 deletions(-)

    diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
    index 6c87c807a0ab..d386853121a2 100644
    --- a/drivers/iommu/intel/svm.c
    +++ b/drivers/iommu/intel/svm.c
    @@ -277,20 +277,16 @@ int intel_svm_bind_gpasid(struct iommu_domain *domain, struct device *dev,
    goto out;
    }

    + /*
    + * Do not allow multiple bindings of the same device-PASID since
    + * there is only one SL page tables per PASID. We may revisit
    + * once sharing PGD across domains are supported.
    + */
    for_each_svm_dev(sdev, svm, dev) {
    - /*
    - * For devices with aux domains, we should allow
    - * multiple bind calls with the same PASID and pdev.
    - */
    - if (iommu_dev_feature_enabled(dev,
    - IOMMU_DEV_FEAT_AUX)) {
    - sdev->users++;
    - } else {
    - dev_warn_ratelimited(dev,
    - "Already bound with PASID %u\n",
    - svm->pasid);
    - ret = -EBUSY;
    - }
    + dev_warn_ratelimited(dev,
    + "Already bound with PASID %u\n",
    + svm->pasid);
    + ret = -EBUSY;
    goto out;
    }
    } else {
    --
    2.7.4
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