intel-iommu: Is this a bug?

[Tushar Dave]

Hi,

I am analyzing network performance with intel-iommu enabled.
And found that running with iommu=pt, for every dma map/unmap it
executes this code:

/*
         * At boot time, we don't yet know if devices will be 64-bit 
capable.
         * Assume that they will â if they turn out not to be, then we can
         * take them out of the 1:1 domain later.
         */
        if (!startup) {
                /*
                 * If the device's dma_mask is less than the system's 
memory
                 * size then this is not a candidate for identity mapping.
                 */
                u64 dma_mask = *dev->dma_mask;

                if (dev->coherent_dma_mask &&
                    dev->coherent_dma_mask < dma_mask)
                        dma_mask = dev->coherent_dma_mask;

                return dma_mask >= dma_get_required_mask(dev);
        }


Do we really need this check for every dma/unmap?
Considering it should be only during startup, shouldn't it be,

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 582fd01..3c8f14e 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -2929,7 +2929,7 @@ static int iommu_should_identity_map(struct device 
*dev, int startup)
         * Assume that they will â if they turn out not to be, then we can
         * take them out of the 1:1 domain later.
         */
-       if (!startup) {
+       if (startup) {
                /*
                 * If the device's dma_mask is less than the system's 
memory
                 * size then this is not a candidate for identity mapping.


Thanks.

-Tushar