Re: [PATCH v2 1/1] powerpc/pseries: fix EEH recovery of some IOV devices

On Mon, Jul 02, 2018 at 10:59:24AM +1000, Michael Ellerman wrote:

Sam Bobroff [off-list ref] writes:

quoted

EEH recovery currently fails on pSeries for some IOV capable PCI
devices, if CONFIG_PCI_IOV is on and the hypervisor doesn't provide
certain device tree properties for the device. (Found on an IOV
capable device using the ipr driver.)

Recovery fails in pci_enable_resources() at the check on r->parent,
because r->flags is set and r->parent is not.  This state is due to
sriov_init() setting the start, end and flags members of the IOV BARs
but the parent not being set later in
pseries_pci_fixup_iov_resources(), because the
"ibm,open-sriov-vf-bar-info" property is missing.

Correct this by zeroing the resource flags for IOV BARs when they
can't be configured.

Signed-off-by: Sam Bobroff <redacted>
---
Hi,

This is a fix to allow EEH recovery to succeed in a specific situation,
which I've tried to explain in the commit message.

As with the RFC version, the IOV BARs are disabled by setting the resource
flags to 0 but the other fields are now left as-is because that is what is done
elsewhere (see sriov_init() and __pci_read_base()).

I've also examined the concern raised by Bjorn Helgaas, that VFs could be
enabled later after the BARs are disabled, and it already seems safe: enabling
VFs (on pseries) depends on another device tree property,
"ibm,number-of-configurable-vfs" as well as support for the RTAS function
"ibm_map_pes". Since these are all part of the hypervisor's support for IOV it
seems unlikely that we would ever see some of them but not all. (None are
currently provided by QEMU/KVM.) (Additionally, the ipr driver on which the EEH
recovery failure was discovered doesn't even seem to have SR-IOV support so it
certainly can't enable VFs.)

Can you fold/reword the above into the change log, it seems like useful
detail.

cheers

Sure, sounds good.