linux-kernel - RE: [PATCH v5 7/8] hisi_acc_vfio_pci: Add support for VFIO live migration

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Message-ID: <60d48005f88a4d63b9a9228c0f4d95b9@huawei.com>
Date:   Wed, 23 Feb 2022 17:07:06 +0000
From:   Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        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>,
        "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 v5 7/8] hisi_acc_vfio_pci: Add support for VFIO live
 migration



> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@...hat.com]
> Sent: 23 February 2022 16:35
> To: Jason Gunthorpe <jgg@...dia.com>
> Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>;
> kvm@...r.kernel.org; linux-kernel@...r.kernel.org;
> linux-crypto@...r.kernel.org; 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 v5 7/8] hisi_acc_vfio_pci: Add support for VFIO live
> migration
> 
> On Tue, 22 Feb 2022 20:52:51 -0400
> Jason Gunthorpe <jgg@...dia.com> wrote:
> 
> > On Mon, Feb 21, 2022 at 11:40:42AM +0000, Shameer Kolothum wrote:
> >
> > > +	/*
> > > +	 * ACC VF dev BAR2 region consists of both functional register space
> > > +	 * and migration control register space. For migration to work, we
> > > +	 * need access to both. Hence, we map the entire BAR2 region here.
> > > +	 * But from a security point of view, we restrict access to the
> > > +	 * migration control space from Guest(Please see mmap/ioctl/read/write
> > > +	 * override functions).
> > > +	 *
> > > +	 * Also the HiSilicon ACC VF devices supported by this driver on
> > > +	 * HiSilicon hardware platforms are integrated end point devices
> > > +	 * and has no capability to perform PCIe P2P.
> >
> > If that is the case why not implement the RUNNING_P2P as well as a
> > NOP?
> >
> > Alex expressed concerned about proliferation of non-P2P devices as it
> > complicates qemu to support mixes
> 
> I read the above as more of a statement about isolation, ie. grouping.

That's right. That's what I meant by " no capability to perform PCIe P2P"

Thanks,
Shameer

> Given that all DMA from the device is translated by the IOMMU, how is
> it possible that a device can entirely lack p2p support, or even know
> that the target address post-translation is to a peer device rather
> than system memory.  If this is the case, it sounds like a restriction
> of the SMMU not supporting translations that reflect back to the I/O
> bus rather than a feature of the device itself.  Thanks,
> 
> Alex