From: Max Gurtovoy <mgurtovoy@nvidia.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Alex Williamson <alex.williamson@redhat.com>,
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: Thu, 30 Sep 2021 12:34:19 +0300 [thread overview]
Message-ID: <d8324d96-c897-b914-16c6-ad0bbb9b13a5@nvidia.com> (raw)
In-Reply-To: <20210929232109.GC3544071@ziepe.ca>
On 9/30/2021 2:21 AM, Jason Gunthorpe wrote:
> On Thu, Sep 30, 2021 at 12:48:55AM +0300, Max Gurtovoy 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.
> Yes, when a vfio_device first opens it must be running - ie able to do
> DMA and otherwise operational.
how can non resumed device do DMA ?
Also the bus master is not set.
>
> When we add the migration extension this cannot change, so after
> open_device() the device should be operational.
if it's waiting for incoming migration blob, it is not running.
>
> The reported state in the migration region should accurately reflect
> what the device is currently doing. If the device is operational then
> it must report running, not stopped.
STOP in migration meaning.
>
> Thus a driver cannot just zero initalize the migration "registers",
> they have to be accurate.
>
>>>> 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 ?
> It seems semantically fine to me, as per Alex's note what will happen
> is defined:
>
> driver will see RESUMING toggle off so it will trigger a
> de-serialization
You mean stop serialization ?
>
> driver will see SAVING toggled on so it will serialize the new state
> (either the pre-copy state or the post-copy state dpending on the
> running bit)
lets leave the bits and how you implement the state numbering aside.
If you finish resuming you can move to a new state (that we should add)
=> RESUMED.
Now you suggested moving from RESUMED to SAVING to get the state again
from the dst device ? and send it back to src ? before staring the VM
and moving to RUNNING ?
where this is coming from ?
>
> Depending on the running bit the device may or may not be woken up.
lets take about logic here and not bits.
>
> If de-serialization fails then the state goes to error and SAVING is
> ignored.
>
> The driver logic probably looks something like this:
>
> // Running toggles off
> if (oldstate & RUNNING != newstate & RUNNING && oldstate & RUNNING)
> queice
> freeze
>
> // Resuming toggles off
> if (oldstate & RESUMING != newstate & RESUMING && oldstate & RESUMING)
> deserialize
>
> // Saving toggles on
> if (oldstate & SAVING != newstate & SAVING && newstate & SAVING)
> if (!(newstate & RUNNING))
> serialize post copy
>
> // Running toggles on
> if (oldstate & RUNNING != newstate & RUNNING && newstate & RUNNING)
> unfreeze
> unqueice
>
> I'd have to check that carefully against the state chart from my last
> email though..
>
> And need to check how the "Stop Active Transactions" bit fits in there
>
> Jason
next prev parent reply other threads:[~2021-09-30 9:34 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
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 [this message]
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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