linux-kernel - Re: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state transition validity

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Message-ID: <20210929161433.GA1808627@ziepe.ca>
Date:   Wed, 29 Sep 2021 13:14:33 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Max Gurtovoy <mgurtovoy@...dia.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Doug Ledford <dledford@...hat.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Kirti Wankhede <kwankhede@...dia.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
        Saeed Mahameed <saeedm@...dia.com>,
        Cornelia Huck <cohuck@...hat.com>
Subject: Re: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state
 transition validity

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"

> 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.

Jason