Re: [PATCH] PCI: Introduce flag for detached virtual functions

Alex Williamson
2020-08-12T16:44:01Z

On Wed, 12 Aug 2020 10:50:17 -0400
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> s390x has the notion of providing VFs to the kernel in a manner
> where the associated PF is inaccessible other than via firmware.
> These are not treated as typical VFs and access to them is emulated
> by underlying firmware which can still access the PF. After
> abafbc55 however these detached VFs were no longer able to work
> with vfio-pci as the firmware does not provide emulation of the
> PCI_COMMAND_MEMORY bit. In this case, let's explicitly recognize
> these detached VFs so that vfio-pci can allow memory access to
> them again.
>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
> Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---
> arch/s390/pci/pci.c | 8 ++++++++
> drivers/vfio/pci/vfio_pci_config.c | 3 ++-
> include/linux/pci.h | 1 +
> 3 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
> index 3902c9f..04ac76d 100644
> --- a/arch/s390/pci/pci.c
> +++ b/arch/s390/pci/pci.c
> @@ -581,6 +581,14 @@ int pcibios_enable_device(struct pci_dev *pdev, int mask)
> {
> struct zpci_dev *zdev = to_zpci(pdev);
>
> + /*
> + * If we have a VF on a non-multifunction bus, it must be a VF that is
> + * detached from its parent PF. We rely on firmware emulation to
> + * provide underlying PF details.
> + */
> + if (zdev->vfn && !zdev->zbus->multifunction)
> + pdev->detached_vf = 1;
> +
> zpci_debug_init_device(zdev, dev_name(&pdev->dev));
> zpci_fmb_enable_device(zdev);
>
> diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> index d98843f..17845fc 100644
> --- a/drivers/vfio/pci/vfio_pci_config.c
> +++ b/drivers/vfio/pci/vfio_pci_config.c
> @@ -406,7 +406,8 @@ bool __vfio_pci_memory_enabled(struct vfio_pci_device *vdev)
> * PF SR-IOV capability, there's therefore no need to trigger
> * faults based on the virtual value.
> */
> - return pdev->is_virtfn || (cmd & PCI_COMMAND_MEMORY);
> + return pdev->is_virtfn || pdev->detached_vf ||
> + (cmd & PCI_COMMAND_MEMORY);
> }
>
> /*

Wouldn't we also want to enable the is_virtfn related code in
vfio_basic_config_read() and at least the initial setting of the
command register in vfio_config_init()? Otherwise we're extending the
incomplete emulation out to userspace. Thanks,

Alex

> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 8355306..23a6972 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -445,6 +445,7 @@ struct pci_dev {
> unsigned int is_probed:1; /* Device probing in progress */
> unsigned int link_active_reporting:1;/* Device capable of reporting link active */
> unsigned int no_vf_scan:1; /* Don't scan for VFs after IOV enablement */
> + unsigned int detached_vf:1; /* VF without local PF access */
> pci_dev_flags_t dev_flags;
> atomic_t enable_cnt; /* pci_enable_device has been called */
>