revert scope for 5.8, was Re: dma-pool fixes

David Rientjes rientjes at
Mon Aug 3 14:30:47 EDT 2020

On Mon, 3 Aug 2020, Christoph Hellwig wrote:

> On Sun, Aug 02, 2020 at 09:14:41PM -0700, David Rientjes wrote:
> > Christoph: since we have atomic DMA coherent pools in 5.8 now, recall our 
> > previous discussions, including Greg KH, regarding backports to stable 
> > trees (we are interested in 5.4 and 5.6) of this support for the purposes 
> > of confidential VM users who wish to run their own SEV-enabled guests in 
> > cloud.
> > 
> > Would you have any objections to backports being offered for this support 
> > now?  We can prepare them immediately.  Or, if you would prefer we hold 
> > off for a while, please let me know and we can delay it until you are more 
> > comfortable.  (For confidential VM users, the ability to run your own 
> > unmodified stable kernel is a much different security story than a guest 
> > modified by the cloud provider.)
> Before we start backporting I think we need the two fixes from
> the "dma pool fixes" series.  Can you start reviewing them?  I also
> think we should probably wait at least until -rc2 for any fallout
> before starting the backport.

Thanks Christoph, this makes perfect sense.  I see Nicolas has refreshed 
the two patches:

dma-pool: fix coherent pool allocations for IOMMU mappings
dma-pool: Only allocate from CMA when in same memory zone

and posted them again today on LKML for review.  I'll review those and 
we'll send a full series of backports for stable consideration for 5.4 LTS 
and 5.6 around 5.9-rc2 timeframe.


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