[PATCH v2] vfio: do not coalesce DMA mappings

[Burakov, Anatoly]

On 2/7/2023 8:56 AM, Gupta, Nipun wrote:
> [AMD Official Use Only - General]
> 
> Hi David,
> 
> I agree that change is not straightforward to review, but it should not cause any functional issue as we are still creating all the memory mappings, but one by one for each segment.
> For hot plug case this causes issue as mentioned, that VFIO does not allow unmap of the individual segments in case mapping was created of a single coalesced segment.
> 
> But yes, I am not sure why this code was added, which Anatoly may have more understanding on.

The motivation behind this code was that Linux allows limited amount of 
page mappings, so we were trying to save on those. However, since then 
there have been a few changes related to partial unmaps that may make it 
so that this code is not only no longer necessary, but is in fact 
actively harmful. I agree that this at least warrants a second look.

> 
> Anatoly,
> 
> Can you please provide your feedback on this change?

The patch probably shouldn't include the mailmap changes :)

Could you please provide some steps to reproduce the hotplug issue 
you're having? It would be great to have a test case for this patchset 
to put it in context.

-- 
Thanks,
Anatoly