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

[Andrea Righi]

Just for the records, this patch wasn't applied to eoan:linux-aws (it's
been applied now), but it was applied only to focal.

So, if you are planning to crank this kernel keep in mind that it needs
a respin to include this patch.

-Andrea

On Thu, Jun 04, 2020 at 03:45:45AM -0400, Khaled Elmously wrote:
> On 2020-05-22 15:34:31 , 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
> > 
> > 
> > -- 
> > kernel-team mailing list
> > kernel-team at lists.ubuntu.com
> > https://lists.ubuntu.com/mailman/listinfo/kernel-team