Re: [PATCH v2] vfio: do not coalesce DMA mappings

[Nipun Gupta <nipun.gupta@amd.com>]

On 4/4/2023 8:43 PM, Burakov, Anatoly wrote:
> Caution: This message originated from an External Source. Use proper 
> caution when opening attachments, clicking links, or responding.
> 
> 
> 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 :)

I see in "git log" that all the mailmap changes are with the patch 
submitted, probably as it shows checkpatch warning, so it seems this 
should be fine?

Thanks,
Nipun

> 
> 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
>