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

[Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>]

> -----Original Message-----
> From: Tian, Kevin [mailto:kevin.tian@intel.com]
> Sent: 29 September 2021 10:06
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>;
> kvm@vger.kernel.org; linux-kernel@vger.kernel.org;
> linux-crypto@vger.kernel.org
> Cc: alex.williamson@redhat.com; jgg@nvidia.com; mgurtovoy@nvidia.com;
> Linuxarm <linuxarm@huawei.com>; liulongfang <liulongfang@huawei.com>;
> Zengtao (B) <prime.zeng@hisilicon.com>; Jonathan Cameron
> <jonathan.cameron@huawei.com>; Wangzhou (B)
> <wangzhou1@hisilicon.com>; He, Shaopeng <shaopeng.he@intel.com>; Zhao,
> Yan Y <yan.y.zhao@intel.com>
> Subject: RE: [PATCH v3 0/6] vfio/hisilicon: add acc live migration driver
> 
> > From: Shameerali Kolothum Thodi
> > <shameerali.kolothum.thodi@huawei.com>
> >
> > Hi Kevin,
> >
> > > From: Tian, Kevin [mailto:kevin.tian@intel.com]
> > > Sent: 29 September 2021 04:58
> > >
> > > Hi, Shameer,
> > >
> > > > From: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> > > > 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.

Yes, the plan is to get the basic live migration working and then we can optimize
it with SMMU HTTU when it is available.

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

Yes. It would be nice to have that info available I guess. But for these devices,
they are integrated end point devices and the platform that supports these
will have SMMUv3 with HTTU.

Thanks,
Shameer

> Thanks
> Kevin