[SRU][F][aws][PATCH 0/1] aws: disable CONFIG_DMA_CMA

[Andrea Righi]

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

[Impact]

The option CONFIG_DMA_CMA seems to cause hibernation failures 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).

With this option disabled the success rate of hibernation on the t2.*
instance types during our tests jumped to 100%.

[Regression potential]

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

----------------------------------------------------------------
Andrea Righi (1):
      UBUNTU: [Config] aws: disable CONFIG_DMA_CMA

 debian.aws/abi/5.4.0-1010.10/amd64/aws.modules |  1 -
 debian.aws/abi/5.4.0-1010.10/arm64/aws.modules |  1 -
 debian.aws/config/config.common.ubuntu         | 11 ++---------
 3 files changed, 2 insertions(+), 11 deletions(-)