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Re: [PATCH v11 05/11] vfio/migration: Block multiple devices migration
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From: |
Jason Gunthorpe |
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Subject: |
Re: [PATCH v11 05/11] vfio/migration: Block multiple devices migration |
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Date: |
Tue, 16 May 2023 08:59:39 -0300 |
On Tue, May 16, 2023 at 10:03:54AM +0000, Shameerali Kolothum Thodi wrote:
> > Currently VFIO migration doesn't implement some kind of intermediate
> > quiescent state in which P2P DMAs are quiesced before stopping or
> > running the device. This can cause problems in multi-device migration
> > where the devices are doing P2P DMAs, since the devices are not stopped
> > together at the same time.
> >
> > Until such support is added, block migration of multiple devices.
>
> Missed this one. Currently this blocks even if the attached devices are not
> capable of P2P DMAs. eg; HiSilicon ACC devices. These are integrated end point
> devices without any P2P capability between them. Is it Ok to check for
> VFIO_MIGRATION_P2P flag and allow if the devices are not supporting that?
Lacking VFIO_MIGRATION_P2P doesn't mean the device is incapable of
P2P, it means the migration can't support P2P.
We'd need some kind of new flag to check and such devices should be
blocked from creating P2P mappings. Basically we don't currently
fully support devices that are incapable of P2P operations.
What happens on your platform if a guest tries to do P2P? Does the
platform crash?
Jason