Comment 0 for bug 1806488

[Impact]
There's a significant performance gain to be had by removing the need to flush the IOMMU TLB on every unmap. I'm seeing a 25% performance gain w/ fio reads on a single NVMe device. This mode of operation is available for x86 via the "intel_iommu=strict" parameter. This support is now available upstream for ARM platforms via the "iommu.strict=[0|1]" parameter, while keeping the default in strict mode.

[Test Case]
$ cat fio.rc
[global]
rw=read
direct=1
ioengine=libaio
iodepth=2048
numjobs=10
bs=4k
group_reporting=1
group_reporting=1
cpumask=0xff
runtime=100
loops = 10000

[job1]
filename=/dev/nvme0n1

[Fix]
44f6876a00e83 iommu/arm-smmu: Support non-strict mode
b2dfeba654cb0 iommu/io-pgtable-arm-v7s: Add support for non-strict mode
9662b99a19abc iommu/arm-smmu-v3: Add support for non-strict mode
b6b65ca20bc93 iommu/io-pgtable-arm: Add support for non-strict mode
68a6efe86f6a1 iommu: Add "iommu.strict" command line option
2da274cdf998a iommu/dma: Add support for non-strict mode
07fdef34d2be6 iommu/arm-smmu-v3: Implement flush_iotlb_all hook
85c7a0f1ef624 iommu/io-pgtable-arm: Fix race handling in split_blk_unmap()

[Regression Risk]