netdev - RE: [PATCH V2 vfio 03/11] vfio: Introduce DMA logging uAPIs

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Date:   Tue, 19 Jul 2022 01:39:07 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Yishai Hadas <yishaih@...dia.com>
CC:     "jgg@...dia.com" <jgg@...dia.com>,
        "saeedm@...dia.com" <saeedm@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "Martins, Joao" <joao.m.martins@...cle.com>,
        "leonro@...dia.com" <leonro@...dia.com>,
        "maorg@...dia.com" <maorg@...dia.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>
Subject: RE: [PATCH V2 vfio 03/11] vfio: Introduce DMA logging uAPIs

> From: Alex Williamson <alex.williamson@...hat.com>
> Sent: Tuesday, July 19, 2022 6:30 AM
> 
> On Thu, 14 Jul 2022 11:12:43 +0300
> Yishai Hadas <yishaih@...dia.com> wrote:
> 
> > DMA logging allows a device to internally record what DMAs the device is
> > initiating and report them back to userspace. It is part of the VFIO
> > migration infrastructure that allows implementing dirty page tracking
> > during the pre copy phase of live migration. Only DMA WRITEs are logged,
> > and this API is not connected to
> VFIO_DEVICE_FEATURE_MIG_DEVICE_STATE.
> >
> > This patch introduces the DMA logging involved uAPIs.
> >
> > It uses the FEATURE ioctl with its GET/SET/PROBE options as of below.
> >
> > It exposes a PROBE option to detect if the device supports DMA logging.
> > It exposes a SET option to start device DMA logging in given IOVAs
> > ranges.
> > It exposes a SET option to stop device DMA logging that was previously
> > started.
> > It exposes a GET option to read back and clear the device DMA log.
> >
> > Extra details exist as part of vfio.h per a specific option.
> 
> 
> Kevin, Kirti, others, any comments on this uAPI proposal?  Are there
> potentially other devices that might make use of this or is everyone
> else waiting for IOMMU based dirty tracking?
> 

I plan to take a look later this week.

>From Intel side I'm not aware of such device so far and IOMMU based
dirty tracking would be the standard way to go.