Re: [PATCH v2 10/22] vfio/pci: Skip reset of preserved device after Live Update

David Matlack
2026-02-27T17:08:22Z

On Fri, Feb 27, 2026 at 7:47 AM Alex Williamson <alex@shazbot.org> wrote:
>
> On Fri, 27 Feb 2026 00:51:18 +0000
> David Matlack <dmatlack@google.com> wrote:
>
> > On 2026-02-26 05:00 PM, Alex Williamson wrote:
> > > On Thu, 29 Jan 2026 21:24:57 +0000
> > > David Matlack <dmatlack@google.com> wrote:
> > > >
> > > > - vdev->reset_works = !ret;
> > > > pci_save_state(pdev);
> > > > vdev->pci_saved_state = pci_store_saved_state(pdev);
> > >
> > > Isn't this a problem too? In the first kernel we store the initial,
> > > post reset state of the device, now we're storing some arbitrary state.
> > > This is the state we're restore when the device is closed.
> >
> > The previous kernel resets the device and restores it back to its
> > post reset state in vfio_pci_liveupdate_freeze() before handing off
> > control to the next kernel. So my intention here is that VFIO will
> > receive the device in that state, allowing it to call
> > pci_store_saved_state() here to capture the post reset state of the
> > device again.
> >
> > Eventually we want to drop the reset in vfio_pci_liveupdate_freeze() and
> > preserve vdev->pci_saved_state across the Live Update. But I was hoping
> > to add that in a follow up series to avoid this one getting too long.
>
> I appreciate reviewing this in smaller chunks, but how does userspace
> know whether the kernel contains a stub implementation of liveupdate or
> behaves according to the end goal?

Would a new VFIO_DEVICE_INFO_CAP be a good way to communicate this
information to userspace?

> Also, didn't we violate our own contract in this patch by adding the
> reset_works field to the serialization data without updating the
> compatibility string? Thanks,

Yes, I will fix that in v3.