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    Subject[PATCH 5.4 08/38] iommu/vt-d: Fix PCI bus rescan device hot add
    Date
    From: Yian Chen <yian.chen@intel.com>

    commit 316f92a705a4c2bf4712135180d56f3cca09243a upstream.

    Notifier calling chain uses priority to determine the execution
    order of the notifiers or listeners registered to the chain.
    PCI bus device hot add utilizes the notification mechanism.

    The current code sets low priority (INT_MIN) to Intel
    dmar_pci_bus_notifier and postpones DMAR decoding after adding
    new device into IOMMU. The result is that struct device pointer
    cannot be found in DRHD search for the new device's DMAR/IOMMU.
    Subsequently, the device is put under the "catch-all" IOMMU
    instead of the correct one. This could cause system hang when
    device TLB invalidation is sent to the wrong IOMMU. Invalidation
    timeout error and hard lockup have been observed and data
    inconsistency/crush may occur as well.

    This patch fixes the issue by setting a positive priority(1) for
    dmar_pci_bus_notifier while the priority of IOMMU bus notifier
    uses the default value(0), therefore DMAR decoding will be in
    advance of DRHD search for a new device to find the correct IOMMU.

    Following is a 2-step example that triggers the bug by simulating
    PCI device hot add behavior in Intel Sapphire Rapids server.

    echo 1 > /sys/bus/pci/devices/0000:6a:01.0/remove
    echo 1 > /sys/bus/pci/rescan

    Fixes: 59ce0515cdaf ("iommu/vt-d: Update DRHD/RMRR/ATSR device scope")
    Cc: stable@vger.kernel.org # v3.15+
    Reported-by: Zhang, Bernice <bernice.zhang@intel.com>
    Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
    Signed-off-by: Yian Chen <yian.chen@intel.com>
    Link: https://lore.kernel.org/r/20220521002115.1624069-1-yian.chen@intel.com
    Signed-off-by: Joerg Roedel <jroedel@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/iommu/dmar.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/iommu/dmar.c
    +++ b/drivers/iommu/dmar.c
    @@ -363,7 +363,7 @@ static int dmar_pci_bus_notifier(struct

    static struct notifier_block dmar_pci_bus_nb = {
    .notifier_call = dmar_pci_bus_notifier,
    - .priority = INT_MIN,
    + .priority = 1,
    };

    static struct dmar_drhd_unit *

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