RE: [PATCH v3 0/6] vfio/hisilicon: add acc live migration driver

[Tian, Kevin]

> From: Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@xxxxxxxxxx>
> 
> Hi Kevin,
> 
> > From: Tian, Kevin [mailto:kevin.tian@xxxxxxxxx]
> > Sent: 29 September 2021 04:58
> >
> > Hi, Shameer,
> >
> > > From: Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx>
> > > Sent: Wednesday, September 15, 2021 5:51 PM
> > >
> > > Hi,
> > >
> > > Thanks to the introduction of vfio_pci_core subsystem framework[0],
> > > now it is possible to provide vendor specific functionality to
> > > vfio pci devices. This series attempts to add vfio live migration
> > > support for HiSilicon ACC VF devices based on the new framework.
> > >
> > > HiSilicon ACC VF device MMIO space includes both the functional
> > > register space and migration control register space. As discussed
> > > in RFCv1[1], this may create security issues as these regions get
> > > shared between the Guest driver and the migration driver.
> > > Based on the feedback, we tried to address those concerns in
> > > this version.
> >
> > This series doesn't mention anything related to dirty page tracking.
> > Are you rely on Keqian's series for utilizing hardware iommu dirty
> > bit (e.g. SMMU HTTU)?
> 
> Yes, this doesn't have dirty page tracking and the plan is to make use of
> Keqian's SMMU HTTU work to improve performance. We have done basic
> sanity testing with those patches.
> 

Do you plan to support migration w/o HTTU as the fallback option? 
Generally one would expect the basic functionality ready before talking
about optimization.

If not, how does userspace know that migration of a given device can 
be allowed only when the iommu supports hardware dirty bit?

Thanks
Kevin