[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 kai.heng.feng at canonical.com
Fri Jul 16 16:58:02 UTC 2021

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

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.

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

Boot an affected system. Kernel panic in Realtek WiFi driver's probe
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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