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

[Andrea Righi]

On Sat, Jul 17, 2021 at 12:58:02AM +0800, Kai-Heng Feng wrote:
> 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.

Applied to impish:linux 5.13.

-Andrea