Re: [PATCH v6 4/5] PCI: Extend isolated function probing to s390

Bjorn Helgaas
2022-07-22T21:13:36Z

On Tue, Jun 28, 2022 at 04:30:59PM +0200, Niklas Schnelle wrote:
> Like the jailhouse hypervisor s390's PCI architecture allows passing
> isolated PCI functions to an OS instance. As of now this is was not
> utilized even with multi-function support as the s390 PCI code makes
> sure that only virtual PCI busses including a function with devfn 0 are
> presented to the PCI subsystem. A subsequent change will remove this
> restriction.
>
> Allow probing such functions by replacing the existing check for
> jailhouse_paravirt() with a new hypervisor_isolated_pci_functions()
> helper.
>
> Cc: Jan Kiszka <jan.kiszka@siemens.com>
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---
> drivers/pci/probe.c | 2 +-
> include/linux/hypervisor.h | 8 ++++++++
> 2 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index a18e07e6a7df..156dd13594b8 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2667,7 +2667,7 @@ int pci_scan_slot(struct pci_bus *bus, int devfn)
> * a hypervisor which passes through individual PCI
> * functions.
> */
> - if (!jailhouse_paravirt())
> + if (!hypervisor_isolated_pci_functions())
> break;
> }
> fn = next_fn(bus, dev, fn);
> diff --git a/include/linux/hypervisor.h b/include/linux/hypervisor.h
> index fc08b433c856..33b1c0482aac 100644
> --- a/include/linux/hypervisor.h
> +++ b/include/linux/hypervisor.h
> @@ -32,4 +32,12 @@ static inline bool jailhouse_paravirt(void)
>
> #endif /* !CONFIG_X86 */
>
> +static inline bool hypervisor_isolated_pci_functions(void)
> +{
> + if (IS_ENABLED(CONFIG_S390))
> + return true;
> + else
> + return jailhouse_paravirt();

It looks kind of wasteful that jailhouse_paravirt() searches the DT
for "jailhouse,cell" several times when I think that's an unchanging
property.

Obviously you didn't add that in this series, and s390 avoids that
cost anyway. But the jailhouse folks might consider optimizing it
somehow.

> +}
> +
> #endif /* __LINUX_HYPEVISOR_H */
> --
> 2.32.0
>