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From: Max Gurtovoy <mgurtovoy@nvidia.com>
To: Alex Williamson <alex.williamson@redhat.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 16:26:55 +0300	[thread overview]
Message-ID: <1eba059c-4743-4675-9f72-1a26b8f3c0f6@nvidia.com> (raw)
In-Reply-To: <20210929063551.47590fbb.alex.williamson@redhat.com>


On 9/29/2021 3:35 PM, Alex Williamson wrote:
> On Wed, 29 Sep 2021 13:44:10 +0300
> Max Gurtovoy <mgurtovoy@nvidia.com> wrote:
>
>> On 9/28/2021 2:12 AM, Jason Gunthorpe wrote:
>>> On Mon, Sep 27, 2021 at 04:46:48PM -0600, Alex Williamson wrote:
>>>>> +	enum { MAX_STATE = VFIO_DEVICE_STATE_RESUMING };
>>>>> +	static const u8 vfio_from_state_table[MAX_STATE + 1][MAX_STATE + 1] = {
>>>>> +		[VFIO_DEVICE_STATE_STOP] = {
>>>>> +			[VFIO_DEVICE_STATE_RUNNING] = 1,
>>>>> +			[VFIO_DEVICE_STATE_RESUMING] = 1,
>>>>> +		},
>>>> Our state transition diagram is pretty weak on reachable transitions
>>>> out of the _STOP state, why do we select only these two as valid?
>>> I have no particular opinion on specific states here, however adding
>>> more states means more stuff for drivers to implement and more risk
>>> driver writers will mess up this uAPI.
>> _STOP == 000b => Device Stopped, not saving or resuming (from UAPI).
>>
>> This is the default initial state and not RUNNING.
>>
>> The user application should move device from STOP => RUNNING or STOP =>
>> RESUMING.
>>
>> Maybe we need to extend the comment in the UAPI file.
>
> include/uapi/linux/vfio.h:
> ...
>   *  +------- _RESUMING
>   *  |+------ _SAVING
>   *  ||+----- _RUNNING
>   *  |||
>   *  000b => Device Stopped, not saving or resuming
>   *  001b => Device running, which is the default state
>                              ^^^^^^^^^^^^^^^^^^^^^^^^^^
> ...
>   * State transitions:
>   *
>   *              _RESUMING  _RUNNING    Pre-copy    Stop-and-copy   _STOP
>   *                (100b)     (001b)     (011b)        (010b)       (000b)
>   * 0. Running or default state
>   *                             |
>                   ^^^^^^^^^^^^^
> ...
>   * 0. Default state of VFIO device is _RUNNING when the user application starts.
>        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> The uAPI is pretty clear here.  A default state of _STOP is not
> compatible with existing devices and userspace that does not support
> migration.  Thanks,

Why do you need this state machine for userspace that doesn't support 
migration ?

What is the definition of RUNNING state for a paused VM that is waiting 
for incoming migration blob ?

>
> Alex
>

  reply	other threads:[~2021-09-29 13:27 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 [this message]
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
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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