intel-iommu: Speed up processing of the identity_mapping function

When there are a large count of PCI devices, and the pass through
option for iommu is set, much time is spent in the identity_mapping
function hunting though the iommu domains to check if a specific
device is "identity mapped".

Speed up the function by checking the cached info to see if
it's mapped to the static identity domain.

Signed-off-by: Mike Travis <travis@sgi.com>
Reviewed-by: Mike Habeck <habeck@sgi.com>
Cc: stable@kernel.org
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
index dcf051d53b74..98be0b55ac0b 100644
--- a/drivers/pci/intel-iommu.c
+++ b/drivers/pci/intel-iommu.c
@@ -2235,10 +2235,10 @@ static int identity_mapping(struct pci_dev *pdev)
         if (likely(!iommu_identity_mapping))
                 return 0;
 
+        info = pdev->dev.archdata.iommu;
+        if (info && info != DUMMY_DEVICE_DOMAIN_INFO)
+                return (info->domain == si_domain);
 
-        list_for_each_entry(info, &si_domain->devices, link)
-                if (info->dev == pdev)
-                        return 1;
         return 0;
 }