** Changed in: linux-aws (Ubuntu Eoan)
Assignee: (unassigned) => Andrea Righi (arighi)
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https://bugs.launchpad.net/bugs/1879711
Title:
aws: disable CONFIG_DMA_CMA
Status in linux-aws package in Ubuntu:
Invalid
Status in linux-aws source package in Eoan:
In Progress
Status in linux-aws source package in Focal:
In Progress
Bug description:
[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.
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