From: Alex Williamson <alex.williamson@redhat.com>
To: Max Gurtovoy <mgurtovoy@nvidia.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>, Leon Romanovsky <leon@kernel.org>,
Doug Ledford <dledford@redhat.com>,
Yishai Hadas <yishaih@nvidia.com>,
Bjorn Helgaas <bhelgaas@google.com>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Kirti Wankhede <kwankhede@nvidia.com>, <kvm@vger.kernel.org>,
<linux-kernel@vger.kernel.org>, <linux-pci@vger.kernel.org>,
<linux-rdma@vger.kernel.org>, <netdev@vger.kernel.org>,
Saeed Mahameed <saeedm@nvidia.com>,
Cornelia Huck <cohuck@redhat.com>
Subject: Re: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state transition validity
Date: Wed, 29 Sep 2021 16:44:09 -0600 [thread overview]
Message-ID: <20210929164409.3c33e311.alex.williamson@redhat.com> (raw)
In-Reply-To: <29835bf4-d094-ae6d-1a32-08e65847b52c@nvidia.com>
On Thu, 30 Sep 2021 00:48:55 +0300
Max Gurtovoy <mgurtovoy@nvidia.com> wrote:
> On 9/29/2021 7:14 PM, Jason Gunthorpe wrote:
> > On Wed, Sep 29, 2021 at 06:28:44PM +0300, Max Gurtovoy wrote:
> >
> >>> So you have a device that's actively modifying its internal state,
> >>> performing I/O, including DMA (thereby dirtying VM memory), all while
> >>> in the _STOP state? And you don't see this as a problem?
> >> I don't see how is it different from vfio-pci situation.
> > vfio-pci provides no way to observe the migration state. It isn't
> > "000b"
>
> Alex said that there is a problem of compatibility.
>
> I migration SW is not involved, nobody will read this migration state.
The _STOP state has a specific meaning regardless of whether userspace
reads the device state value. I think what you're suggesting is that
the device reports itself as _STOP'd but it's actually _RUNNING. Is
that the compatibility workaround, create a self inconsistency?
We cannot impose on userspace to move a device from _STOP to _RUNNING
simply because the device supports the migration region, nor should we
report a device state that is inconsistent with the actual device state.
> >> Maybe we need to rename STOP state. We can call it READY or LIVE or
> >> NON_MIGRATION_STATE.
> > It was a poor choice to use 000b as stop, but it doesn't really
> > matter. The mlx5 driver should just pre-init this readable to running.
>
> I guess we can do it for this reason. There is no functional problem nor
> compatibility issue here as was mentioned.
>
> But still we need the kernel to track transitions. We don't want to
> allow moving from RESUMING to SAVING state for example. How this
> transition can be allowed ?
>
> In this case we need to fail the request from the migration SW...
_RESUMING to _SAVING seems like a good way to test round trip migration
without running the device to modify the state. Potentially it's a
means to update a saved device migration data stream to a newer format
using an intermediate driver version.
If a driver is written such that it simply sees clearing the _RESUME
bit as an indicator to de-serialize the data stream to the device, and
setting the _SAVING flag as an indicator to re-serialize that data
stream from the device, then this is just a means to make use of
existing data paths.
The uAPI specifies a means for drivers to reject a state change, but
that risks failing to support a transition which might find mainstream
use cases. I don't think common code should be responsible for
filtering out viable transitions. Thanks,
Alex
next prev parent reply other threads:[~2021-09-29 22:44 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1632305919.git.leonro@nvidia.com>
2021-09-22 10:38 ` [PATCH mlx5-next 1/7] PCI/IOV: Provide internal VF index Leon Romanovsky
2021-09-22 21:59 ` Bjorn Helgaas
2021-09-23 6:35 ` Leon Romanovsky
2021-09-24 13:08 ` Bjorn Helgaas
2021-09-25 10:10 ` Leon Romanovsky
2021-09-25 17:41 ` Bjorn Helgaas
2021-09-26 6:36 ` Leon Romanovsky
2021-09-26 20:23 ` Bjorn Helgaas
2021-09-27 11:55 ` Leon Romanovsky
2021-09-27 14:47 ` Bjorn Helgaas
2021-09-22 10:38 ` [PATCH mlx5-next 2/7] vfio: Add an API to check migration state transition validity Leon Romanovsky
2021-09-23 10:33 ` Shameerali Kolothum Thodi
2021-09-23 11:17 ` Leon Romanovsky
2021-09-23 13:55 ` Max Gurtovoy
2021-09-24 7:44 ` Shameerali Kolothum Thodi
2021-09-24 9:37 ` Kirti Wankhede
2021-09-26 9:09 ` Max Gurtovoy
2021-09-26 16:17 ` Shameerali Kolothum Thodi
2021-09-27 18:24 ` Max Gurtovoy
2021-09-27 18:29 ` Shameerali Kolothum Thodi
2021-09-27 22:46 ` Alex Williamson
2021-09-27 23:12 ` Jason Gunthorpe
2021-09-28 19:19 ` Alex Williamson
2021-09-28 19:35 ` Jason Gunthorpe
2021-09-28 20:18 ` Alex Williamson
2021-09-29 16:16 ` Jason Gunthorpe
2021-09-29 18:06 ` Alex Williamson
2021-09-29 18:26 ` Jason Gunthorpe
2021-09-29 10:57 ` Max Gurtovoy
2021-09-29 10:44 ` Max Gurtovoy
2021-09-29 12:35 ` Alex Williamson
2021-09-29 13:26 ` Max Gurtovoy
2021-09-29 13:50 ` Alex Williamson
2021-09-29 14:36 ` Max Gurtovoy
2021-09-29 15:17 ` Alex Williamson
2021-09-29 15:28 ` Max Gurtovoy
2021-09-29 16:14 ` Jason Gunthorpe
2021-09-29 21:48 ` Max Gurtovoy
2021-09-29 22:44 ` Alex Williamson [this message]
2021-09-30 9:25 ` Max Gurtovoy
2021-09-30 12:41 ` Alex Williamson
2021-09-29 23:21 ` Jason Gunthorpe
2021-09-30 9:34 ` Max Gurtovoy
2021-09-30 14:47 ` Jason Gunthorpe
2021-09-30 15:32 ` Max Gurtovoy
2021-09-30 16:24 ` Jason Gunthorpe
2021-09-30 16:51 ` Max Gurtovoy
2021-09-30 17:01 ` Jason Gunthorpe
2021-09-22 10:38 ` [PATCH mlx5-next 3/7] vfio/pci_core: Make the region->release() function optional Leon Romanovsky
2021-09-23 13:57 ` Max Gurtovoy
2021-09-22 10:38 ` [PATCH mlx5-next 4/7] net/mlx5: Introduce migration bits and structures Leon Romanovsky
2021-09-24 5:48 ` Mark Zhang
2021-09-22 10:38 ` [PATCH mlx5-next 5/7] net/mlx5: Expose APIs to get/put the mlx5 core device Leon Romanovsky
2021-09-22 10:38 ` [PATCH mlx5-next 6/7] mlx5_vfio_pci: Expose migration commands over mlx5 device Leon Romanovsky
2021-09-28 20:22 ` Alex Williamson
2021-09-29 5:36 ` Leon Romanovsky
2021-09-22 10:38 ` [PATCH mlx5-next 7/7] mlx5_vfio_pci: Implement vfio_pci driver for mlx5 devices Leon Romanovsky
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