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Subject: Re: [PATCH v3 6/8] admin: Add theory of operation for write recording commands
On Mon, Oct 30, 2023 at 9:21âPM Parav Pandit <parav@nvidia.com> wrote: > > During a device migration flow (typically in a precopy phase of the > live migration), a device may write to the guest memory. Some > iommu/hypervisor may not be able to track these written pages. > These pages to be migrated from source to destination hypervisor. > > A device which writes to these pages, provides the page address record > of the to the owner device. The owner device starts write > recording for the device and queries all the page addresses written by > the device. > > Fixes: https://github.com/oasis-tcs/virtio-spec/issues/176 > Signed-off-by: Parav Pandit <parav@nvidia.com> > Signed-off-by: Satananda Burla <sburla@marvell.com> > --- > changelog: > v1->v2: > - addressed comments from Michael > - replaced iova with physical address > --- > admin-cmds-device-migration.tex | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/admin-cmds-device-migration.tex b/admin-cmds-device-migration.tex > index ed911e4..2e32f2c 100644 > --- a/admin-cmds-device-migration.tex > +++ b/admin-cmds-device-migration.tex > @@ -95,6 +95,21 @@ \subsubsection{Device Migration}\label{sec:Basic Facilities of a Virtio Device / > The owner driver can discard any partially read or written device context when > any of the device migration flow should be aborted. > > +During the device migration flow, a passthrough device may write data to the > +guest virtual machine's memory, a source hypervisor needs to keep track of these > +written memory to migrate such memory to destination hypervisor. > +Some systems may not be able to keep track of such memory write addresses at > +hypervisor level. In such a scenario, a device records and reports these > +written memory addresses to the owner device. The owner driver enables write > +recording for one or more physical address ranges per device during device > +migration flow. The owner driver periodically queries these written physical > +address records from the device. I wonder how PA works in this case. Device uses untranslated requests so it can only see IOVA. We can't mandate ATS anyhow. Thanks
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