** Description changed:
[Impact]
To properly support instance types in AWS with > 255 cores we need to
make sure that commit c40aaaac1018ff1382f2d35df5129a6bcea3df6b
("iommu/vt-d: Gracefully handle DMAR units with no supported address
widths") is applied across all our linux-aws kernels.
[Test Case]
Tests performed by AWS.
[Fix]
Apply/backport commit c40aaaac1018ff1382f2d35df5129a6bcea3df6b.
+ For groovy it's a clean cherry pick.
+
+ For Focal/Bionic the backport activity is to simply rename the patched
+ file.
+
+ Only Xenial requires a little more backporting activity, in particular
+ we need to change the condition in free_iommu() checking if
+ iommu->iommu_dev is defined (instead of checking for iommu->iommu.ops,
+ that is not available in the 4.4 kernel).
+
[Regression potential]
- The fix is affecting only intel IOMMU and it is an upstream fix, so the
- regression potential is minimal.
+ This change allows to use DMAR units that were not used before (for
+ interrupt remapping). Theoretically this should provide a performance
+ improvement, but we should keep an eye about potential performance
+ regressions of drivers that are using IOMMU, in case they're using this
+ new behavior incorrectly.
+
+ Moreover, the Xenial backport required an adjustment in free_iommu() to
+ check when we need to call iommu_device_destroy(), if the adjustment is
+ not 100% correct we could introduce a potential memory leak.
** No longer affects: linux-aws (Ubuntu Hirsute)
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https://bugs.launchpad.net/bugs/1913739
Title:
aws: properly support instance types with > 255 cpu cores
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