On 06/23/2014 03:09 PM, Bjorn Helgaas wrote:
[+cc linux-pci, Don]
Adding Alex Williamson in case he can add more to this conversation...
On Mon, Jun 23, 2014 at 8:29 AM, Yishai Hadas <yishaih@xxxxxxxxxxxxxxxxxx> wrote:Hi Vijay, Trying to add AER support for Mellanox NIC in SRIOV environment, while evaluating/testing encountered a problem which led me to your patch accepted as part of kernel 3.8, commit ID "918b4053184c0ca22236e70e299c5343eea35304". Have some concerns/questions on: When working in SRIOV environment VFs may be un-attached, having no driver assigned to, or may be attached to Virtual machine to work in some pass-through mode. Once working in KVM setup there is pci-stub driver which is loaded in the HYP/PF for a given attached VF.
huh? 'loaded in the hyp/pf? .... um, loaded in the host, and a VF is detached from its host driver -- a VF can be used in the host w/o any virtualization, i.e., that's how guest VM is driving the VF: as if it was used by a guest (host) OS directly -- and attached to pci-stub driver, when assigned to a KVM guest in pre-VFIO days/ways. If VFIO used, then VF is attached to vfio-pci driver.
I'm using the aer-inject kernel module and its corresponding aer-inject tool to simulate an error in the HYP. In both cases your commit will cause the AER recovery to fail as there is no driver assigned to PF's VFs that supports AER, comparing the code before your change.
Without VFIO, I believe that's correct. There was no AER-to-VF support pre-VFIO days. I believe with the recent VFIO support, and modifications to KVM, an AER that is associated with an assigned VF will force the crash/halt of the KVM guest -- can't depend on a guest VF driver clearing the AER in the hyp/host -- guest isn't privileged enough to clear the error. So, crashing the guest is the simple option at the moment, to contain the error. Alex: do I have that (vfio aer default) correct, or is that still site-under-construction?
How such cases should work ? my expectation was that the PF will get the error detected message then will recognize whether issue is its own or one of its VFs
The AER packet will have the tag of the VF in if it was the source of the error;
so the PF will never see it; although one could argue it should be 'promoted'
to the PF if PF/VF needs to clear some state it has wrt the VF (the SRIOV spec is
lacking of info in this space); _but_, VFIO resets the VF (sets FLR bit) when the
device is deassigned and before re-attachment to the host, so that should clear out
any state btwn PF & VF ('should' ... famous last words...).
I'm really not an AER expert, so help me understand this question of recognizing whether an error is associated with a PF or a VF. In terms of hardware, it looks like the device that detects an error logs some information and sends an Error Message upstream. The Root Complex receives the message, captures the source ID from the Error Message, and may generate an interrupt. I expect this source ID can be either a PF or a VF; there's no requirement that a VF error must be reported as though it's from the PF, is there?and work accordingly, in current code looks like recovery failed as part of "voting" once there is no AER handler assigned to the VFs.The commit you mentioned has to do with PCI_ERS_RESULT_NO_AER_DRIVER. We use pci_walk_bus() to figure out whether all the devices in a subtree have a driver. What subtree is involved here? I would expect the VFs to be siblings of the PF, not children of it, so I'm not sure where things went wrong.
Well, VFs could be on virtual busses (ARI turned on), so not necessarily a sibling to PF ... and then we have the problem in PCI code of not being able to traverse these virtual busses (in some cases; not sure if pci_walk_bus(), which is going down the tree vs up the tree, has any problems here w/VFs on virtual busses).
Can you collect "lspci -vvv" output and maybe add some debug so we can see exactly where the error is detected and what devices we're looking at to conclude that one of them doesn't have a driver? Bjorn
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