On Tue, Jul 30, 2024 at 09:59:13PM +0200, Niklas Schnelle wrote:
> On Tue, 2024-07-30 at 21:36 +0200, Niklas Schnelle wrote:
> > On s390 PCI busses are virtualized and the downstream ports are
> > invisible to the OS and struct pci_bus::self is NULL. This associated
> > struct pci_dev is however relied upon in pci_ari_enabled() to check
> > whether ARI is enabled for the bus. ARI is therefor always detected as
> > disabled.
> >
> > At the same time firmware on s390 always enables and relies upon ARI
> > thus causing a mismatch. Moreover with per-PCI function pass-through
> > there may exist busses with no function with devfn 0. For example
> > a SR-IOV capable device with two PFs may have separate function
> > dependency link chains for each of the PFs and their child VFs. In this
> > case the OS may only see the second PF and its child VFs on a bus
> > without a devfn 0 function. A situation which is also not supported by
> > the common pci_configure_ari() code.
> >
> > Dispite simply being a mismatch this causes problems as some PCI devices
> > present a different SR-IOV topology depending on PCI_SRIOV_CTRL_ARI.
> >
> > A similar mismatch may occur with SR-IOV when virtfn_add_bus() creates new
> > busses with no associated struct pci_dev. Here too pci_ari_enabled()
> > on these busses would return false even if ARI is actually used.
> >
> > Prevent both mismatches by moving the ari_enabled flag from struct
> > pci_dev to struct pci_bus making it independent from struct pci_bus::
> > self. Let the bus inherit the ari_enabled state from its parent bus when
> > there is no bridge device such that busses added by virtfn_add_bus()
> > match their parent. For s390 set ari_enabled when the device supports
> > ARI in the awareness that all PCIe ports on s390 systems are ARI
> > capable.
> >
> > Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> > ---
> > arch/s390/pci/pci_bus.c | 12 ++++++++++++
> > drivers/pci/pci.c | 4 ++--
> > drivers/pci/probe.c | 1 +
> > include/linux/pci.h | 4 ++--
> > 4 files changed, 17 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/s390/pci/pci_bus.c b/arch/s390/pci/pci_bus.c
> > index daa5d7450c7d..021319438dad 100644
> > --- a/arch/s390/pci/pci_bus.c
> > +++ b/arch/s390/pci/pci_bus.c
> > @@ -278,6 +278,18 @@ void pcibios_bus_add_device(struct pci_dev *pdev)
> > {
> > struct zpci_dev *zdev = to_zpci(pdev);
> >
> > + /*
> > + * On s390 PCI busses are virtualized and the bridge
> > + * devices are invisible to the OS. Furthermore busses
> > + * may exist without a devfn 0 function. Thus the normal
> > + * ARI detection does not work. At the same time fw/hw
> > + * has always enabled ARI when possible. Reflect the actual
> > + * state by setting ari_enabled whenever a device on the bus
> > + * supports it.
> > + */
> > + if (pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_ARI))
> > + zdev->zbus->bus->ari_enabled = 1;
> > +
>
> @Bjorn unstead of adding the above code to s390 specific code an
> alternative I considered would be to modify pci_configure_ari() like
> below. I tested this as well but wasn't sure if it is too much churn
> especially the handling of the dev->devfn != 0 case. Then again it
> might be nice to have this in common code.
>
> @@ -3523,12 +3524,18 @@ void pci_configure_ari(struct pci_dev *dev)
> u32 cap;
> struct pci_dev *bridge;
>
> - if (pcie_ari_disabled || !pci_is_pcie(dev) || dev->devfn)
> + if (pcie_ari_disabled || !pci_is_pcie(dev))
> + return;
> +
> + if (dev->devfn && !hypervisor_isolated_pci_functions())
> return;
>
> bridge = dev->bus->self;
> - if (!bridge)
> + if (!bridge) {
> + if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ARI))
> + dev->bus->ari_enabled = 1;
In the generic case here, how do we know whether the invisible bridge
leading here has ARI enabled? If that's known to always be the case
for s390, I understand that, but I don't understand the other cases
(jailhouse, passthrough, etc).
> return;
> + }
>
> pcie_capability_read_dword(bridge, PCI_EXP_DEVCAP2, &cap);
> if (!(cap & PCI_EXP_DEVCAP2_ARI))
>
