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

["Gupta, Nipun" <Nipun.Gupta@amd.com>]

Hi David,
	As the DPDK 23.03 release is out can we have a relook at this change?

Thanks,
Nipun

> -----Original Message-----
> From: Gupta, Nipun
> Sent: Tuesday, February 7, 2023 2:27 PM
> To: David Marchand <david.marchand@redhat.com>;
> anatoly.burakov@intel.com
> Cc: dev@dpdk.org; thomas@monjalon.net; Yigit, Ferruh
> <Ferruh.Yigit@amd.com>; Agarwal, Nikhil <nikhil.agarwal@amd.com>
> Subject: RE: [PATCH v2] vfio: do not coalesce DMA mappings
> 
> [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.
> 
> Anatoly,
> 
> Can you please provide your feedback on this change?
> 
> Thanks,
> Nipun
> 
> > -----Original Message-----
> > From: David Marchand <david.marchand@redhat.com>
> > Sent: Thursday, February 2, 2023 4:19 PM
> > To: anatoly.burakov@intel.com; Gupta, Nipun <Nipun.Gupta@amd.com>
> > Cc: dev@dpdk.org; thomas@monjalon.net; Yigit, Ferruh
> > <Ferruh.Yigit@amd.com>; Agarwal, Nikhil <nikhil.agarwal@amd.com>
> > Subject: Re: [PATCH v2] vfio: do not coalesce DMA mappings
> >
> > Caution: This message originated from an External Source. Use proper caution
> > when opening attachments, clicking links, or responding.
> >
> >
> > Hi,
> >
> > On Wed, Jan 4, 2023 at 6:19 AM Nipun Gupta <nipun.gupta@amd.com>
> wrote:
> > >
> > > At the cleanup time when dma unmap is done, linux kernel
> > > does not allow unmap of individual segments which were
> > > coalesced together while creating the DMA map for type1 IOMMU
> > > mappings. So, this change updates the mapping of the memory
> > > segments(hugepages) on a per-page basis.
> > >
> > > Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
> > > Signed-off-by: Nikhil Agarwal <nikhil.agarwal@amd.com>
> >
> > This change is scary.
> >
> > I won't take it without a review from the maintainer.
> > Anatoly, can you have a look?
> >
> >
> > Thanks.
> > --
> > David Marchand