[SRU] [H/I/Unstable/OEM-5.10/OEM-5.13] [PATCH 0/1] Fix kernel panic caused by legacy devices on AMD platforms

[Kai-Heng Feng]

BugLink: https://bugs.launchpad.net/bugs/1936682

[Impact]
When a legacy device is only 32bit DMA capable and it's in the same
IOMMU group with iommu_v2 capable devices, the device in question will
be forced to use identity mapping and triggers kernel panic on DMA
operation because it can't do 64bit DMA.

[Fix]
Keep swiotlb enabled so legacy devices can do 64bit DMA. This is also
how Intel and ARM64 platforms deal with legacy devices.

[Test]
Boot an affected system. Kernel panic in Realtek WiFi driver's probe
routine.
After the patch is applied, the system can work normally.

[Where problems could occur]
The default swiotlb uses 64MB memory, so if the system doesn't have any
legacy device, there are 64MB ram less for the system to use.

Kai-Heng Feng (1):
  UBUNTU: SAUCE: iommu/amd: Keep swiotlb enabled to ensure devices with
    32bit DMA still work

 drivers/iommu/amd/iommu.c | 2 --
 1 file changed, 2 deletions(-)

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2.31.1