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    SubjectRe: [PATCH v3 8/8] vfio/pci: Add the support for PCI D3cold state
    On Wed, Jun 01, 2022 at 10:21:51AM -0600, Alex Williamson wrote:

    > Some ioctls clearly cannot occur while the device is in low power, such
    > as resets and interrupt control, but even less obvious things like
    > getting region info require device access. Migration also provides a
    > channel to device access.

    I wonder what power management means in a case like that.

    For the migration drivers they all rely on a PF driver that is not
    VFIO, so it should be impossible for power management to cause the PF
    to stop working.

    I would expect any sane design of power management for a VF to not
    cause any harm to the migration driver..

    > I'm also still curious how we're going to handle devices that cannot
    > return to low power such as the self-refresh mode on the GPU. We can
    > potentially prevent any wake-ups from the vfio device interface, but
    > that doesn't preclude a wake-up via an external lspci. I think we need
    > to understand how we're going to handle such devices before we can
    > really complete the design. AIUI, we cannot disable the self-refresh
    > sleep mode without imposing unreasonable latency and memory
    > requirements on the guest and we cannot retrigger the self-refresh
    > low-power mode without non-trivial device specific code.

    It begs the question if power management should be something that only
    a device-specific drivers should allow?

    Jason

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