Re: [Intel-gfx] [PATCH v4 09/14] vfio/pci: Change vfio_pci_try_bus_reset() to use the dev_set

[Cornelia Huck <cohuck@redhat.com>]

On Thu, Aug 05 2021, Jason Gunthorpe <jgg@nvidia.com> wrote:

> vfio_pci_try_bus_reset() is triggering a reset of the entire_dev set if
> any device within it has accumulated a needs_reset. This reset can only be
> done once all of the drivers operating the PCI devices to be reset are in
> a known safe state.
>
> Make this clearer by directly operating on the dev_set instead of the
> vfio_pci_device. Rename the function to vfio_pci_dev_set_try_reset().
>
> Use the device list inside the dev_set to check that all drivers are in a
> safe state instead of working backwards from the pci_device.
>
> The dev_set->lock directly prevents devices from joining/leaving the set,
> or changing their state, which further implies the pci_device cannot
> change drivers or that the vfio_device be freed, eliminating the need for
> get/put's.
>
> If a pci_device to be reset is not in the dev_set then the reset cannot be
> used as we can't know what the state of that driver is. Directly measure
> this by checking that every pci_device is in the dev_set - which
> effectively proves that VFIO drivers are attached to everything.
>
> Remove the odd interaction around vfio_pci_set_power_state() - have the
> only caller avoid its redundant vfio_pci_set_power_state() instead of
> avoiding it inside vfio_pci_dev_set_try_reset().
>
> This restructuring corrects a call to pci_dev_driver() without holding the
> device_lock() and removes a hard wiring to &vfio_pci_driver.
>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>  drivers/vfio/pci/vfio_pci.c | 182 +++++++++++++++++-------------------
>  1 file changed, 86 insertions(+), 96 deletions(-)

Reviewed-by: Cornelia Huck <cohuck@redhat.com>