Public bug reported:

[Impact]

The option CONFIG_DMA_CMA seems to cause resume problems on the t2.*
instance types (Xen).

With this option enabled device drivers are allowed to use the Contiguous 
Memory Allocator (CMA) for DMA operations. So, drivers can allocate large 
physically-contiguous blocks of memory, instead of relying on the I/O map or 
scatter-gather support.
    
However, on resume, the memory used by DMA needs to be re-initialized / 
re-allocated, but it may fail to allocate large chunks of contiguous memory due 
to the fact that we also need to restore the hibernation image, using more 
memory and causing a system hang during the resume process.

[Test case]

Hibernate / resume any t2.* instance (especially t2.nano, where the
problem seems to happen 100% of the times after 2 consecutive
hibernate/resume cycles).

[Fix]

Disable CONFIG_DMA_CMA.

NOTE: this option is already disabled in the generic kernel (see LP:
#1362261).

[Regression potential]

It is a .config change, no regression potential except with the fact
that disabling this option also disables the module 'etnaviv' (Vivante
graphic card), that is not really needed in the aws kernel.

** Affects: linux-aws (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: linux-aws (Ubuntu Focal)
     Importance: High
     Assignee: Andrea Righi (arighi)
         Status: New

** Also affects: linux (Ubuntu Focal)
   Importance: Undecided
       Status: New

** Package changed: linux (Ubuntu) => linux-aws (Ubuntu)

** Changed in: linux-aws (Ubuntu Focal)
   Importance: Undecided => High

** Changed in: linux-aws (Ubuntu Focal)
     Assignee: (unassigned) => Andrea Righi (arighi)

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https://bugs.launchpad.net/bugs/1879711

Title:
  aws: disable CONFIG_DMA_CMA

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