ACK: [SRU][F/E][aws][PATCH v2 0/1] aws: disable CONFIG_DMA_CMA

[Stefan Bader]

On 22.05.20 15:34, Andrea Righi wrote:
> 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 on amd64 and re-align config and annotations file
> with master kernel.
> 
> 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.
> 
> Changes in v2:
>  - disable CONFIG_DMA_CMA only on amd64 and re-align annotations file
>    with master kernel
>  - provide patch for eoan:linux-aws
> 
> 
Acked-by: Stefan Bader <stefan.bader at canonical.com>

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