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Date: Thu, 3 Mar 2022 13:27:47 +0000
From: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
"cohuck@...hat.com" <cohuck@...hat.com>,
"mgurtovoy@...dia.com" <mgurtovoy@...dia.com>,
"yishaih@...dia.com" <yishaih@...dia.com>,
Linuxarm <linuxarm@...wei.com>,
liulongfang <liulongfang@...wei.com>,
"Zengtao (B)" <prime.zeng@...ilicon.com>,
Jonathan Cameron <jonathan.cameron@...wei.com>,
"Wangzhou (B)" <wangzhou1@...ilicon.com>
Subject: RE: [PATCH v7 09/10] hisi_acc_vfio_pci: Add support for VFIO live
migration
> -----Original Message-----
> From: Jason Gunthorpe [mailto:jgg@...dia.com]
> Sent: 03 March 2022 13:20
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
> Cc: kvm@...r.kernel.org; linux-kernel@...r.kernel.org;
> linux-crypto@...r.kernel.org; linux-pci@...r.kernel.org;
> alex.williamson@...hat.com; cohuck@...hat.com; mgurtovoy@...dia.com;
> yishaih@...dia.com; Linuxarm <linuxarm@...wei.com>; liulongfang
> <liulongfang@...wei.com>; Zengtao (B) <prime.zeng@...ilicon.com>;
> Jonathan Cameron <jonathan.cameron@...wei.com>; Wangzhou (B)
> <wangzhou1@...ilicon.com>
> Subject: Re: [PATCH v7 09/10] hisi_acc_vfio_pci: Add support for VFIO live
> migration
>
> On Thu, Mar 03, 2022 at 01:17:05PM +0000, Shameerali Kolothum Thodi
> wrote:
> > > Tthere is a scenario that transfers only QM_MATCH_SIZE in stop_copy?
> > > This doesn't seem like a good idea, I think you should transfer a
> > > positive indication 'this device is not ready' instead of truncating
> > > the stream. A truncated stream should not be a valid stream.
> > >
> > > ie always transfer the whole struct.
> >
> > We could add a 'qm_state' and return the whole struct. But the rest
> > of the struct is basically invalid if qm_state = QM_NOT_REDAY.
>
> This seems like the right thing to do to me
>
> > > > Looks like setting the total_length = 0 in STOP_COPY is a better
> > > > solution(If there are no other issues with that) as it will avoid
> > > > grabbing the state_mutex as you mentioned above.
> > >
> > > That seems really weird, I wouldn't recommend doing that..
> >
> > Does that mean we don't support a zero data transfer in STOP_COPY?
>
> total_length should not go backwards
>
> > The concern is if we always transfer the whole struct, we end up reading
> > and writing the whole thing even if most of the data is invalid.
>
> Well, you can't know if the device is not ready or not until the
> reaching STOP_COPY, so you have to transfer something to avoid
> truncating the data stream. The state here is tiny, is the extra
> transfer a real worry?
Ok, don't think so. I will introduce the 'qm_state' and handle it as discussed
above then.
Thanks,
Shameer
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