linux-kernel - Re: [RFC PATCH V2 0/3] IXGBE/VFIO: Add live migration support for SRIOV NIC

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Date:	Wed, 9 Dec 2015 12:37:46 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	"Lan, Tianyu" <tianyu.lan@...el.com>
Cc:	Alexander Duyck <alexander.duyck@...il.com>,
	"Dong, Eddie" <eddie.dong@...el.com>,
	"a.motakis@...tualopensystems.com" <a.motakis@...tualopensystems.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	"b.reynal@...tualopensystems.com" <b.reynal@...tualopensystems.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Wyborny, Carolyn" <carolyn.wyborny@...el.com>,
	"Skidmore, Donald C" <donald.c.skidmore@...el.com>,
	"Jani, Nrupal" <nrupal.jani@...el.com>,
	Alexander Graf <agraf@...e.de>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"Tantilov, Emil S" <emil.s.tantilov@...el.com>,
	Or Gerlitz <gerlitz.or@...il.com>,
	"Rustad, Mark D" <mark.d.rustad@...el.com>,
	Eric Auger <eric.auger@...aro.org>,
	intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Williams, Mitch A" <mitch.a.williams@...el.com>,
	Netdev <netdev@...r.kernel.org>,
	"Nelson, Shannon" <shannon.nelson@...el.com>,
	Wei Yang <weiyang@...ux.vnet.ibm.com>,
	"zajec5@...il.com" <zajec5@...il.com>
Subject: Re: [RFC PATCH V2 0/3] IXGBE/VFIO: Add live migration support for
 SRIOV NIC

On Sat, Dec 05, 2015 at 12:32:00AM +0800, Lan, Tianyu wrote:
> Hi Michael & Alexander:
> Thanks a lot for your comments and suggestions.

It's nice that it's appreciated, but you then go on and ignore
all that I have written here:
https://www.mail-archive.com/kvm@vger.kernel.org/msg123826.html

> We still need to support Windows guest for migration and this is why our
> patches keep all changes in the driver since it's impossible to change
> Windows kernel.

This is not a reasonable argument.  It makes no sense to duplicate code
on Linux because you must duplicate code on Windows.  Let's assume you
must do it in the driver on windows because windows has closed source
drivers.  What does it matter? Linux can still do it as part of DMA API
and have it apply to all drivers.

> Following is my idea to do DMA tracking.
> 
> Inject event to VF driver after memory iterate stage
> and before stop VCPU and then VF driver marks dirty all
> using DMA memory. The new allocated pages also need to
> be marked dirty before stopping VCPU. All dirty memory
> in this time slot will be migrated until stop-and-copy
> stage. We also need to make sure to disable VF via clearing the
> bus master enable bit for VF before migrating these memory.
> 
> The dma page allocated by VF driver also needs to reserve space
> to do dummy write.

I suggested ways to do it all in the hypervisor without driver hacks, or
hide it within DMA API without need to reserve extra space. Both
approaches seem much cleaner.

-- 
MST
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