Re: [PATCH][v2] iommu: arm-smmu-v3: Copy SMMU table for kdump kernel

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, May 27, 2020 at 05:14:39PM +0530, Prabhakar Kushwaha wrote:
> On Fri, May 22, 2020 at 4:19 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > On Thu, May 21, 2020 at 09:28:20AM +0530, Prabhakar Kushwaha wrote:
> > > On Wed, May 20, 2020 at 4:52 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > > > On Thu, May 14, 2020 at 12:47:02PM +0530, Prabhakar Kushwaha wrote:
> > > > > On Wed, May 13, 2020 at 3:33 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > > > > > On Mon, May 11, 2020 at 07:46:06PM -0700, Prabhakar Kushwaha wrote:
> > > > > > > An SMMU Stream table is created by the primary kernel. This table is
> > > > > > > used by the SMMU to perform address translations for device-originated
> > > > > > > transactions. Any crash (if happened) launches the kdump kernel which
> > > > > > > re-creates the SMMU Stream table. New transactions will be translated
> > > > > > > via this new table..
> > > > > > >
> > > > > > > There are scenarios, where devices are still having old pending
> > > > > > > transactions (configured in the primary kernel). These transactions
> > > > > > > come in-between Stream table creation and device-driver probe.
> > > > > > > As new stream table does not have entry for older transactions,
> > > > > > > it will be aborted by SMMU.
> > > > > > >
> > > > > > > Similar observations were found with PCIe-Intel 82576 Gigabit
> > > > > > > Network card. It sends old Memory Read transaction in kdump kernel.
> > > > > > > Transactions configured for older Stream table entries, that do not
> > > > > > > exist any longer in the new table, will cause a PCIe Completion Abort.
> > > > > >
> > > > > > That sounds like exactly what we want, doesn't it?
> > > > > >
> > > > > > Or do you *want* DMA from the previous kernel to complete?  That will
> > > > > > read or scribble on something, but maybe that's not terrible as long
> > > > > > as it's not memory used by the kdump kernel.
> > > > >
> > > > > Yes, Abort should happen. But it should happen in context of driver.
> > > > > But current abort is happening because of SMMU and no driver/pcie
> > > > > setup present at this moment.
> > > >
> > > > I don't understand what you mean by "in context of driver."  The whole
> > > > problem is that we can't control *when* the abort happens, so it may
> > > > happen in *any* context.  It may happen when a NIC receives a packet
> > > > or at some other unpredictable time.
> > > >
> > > > > Solution of this issue should be at 2 place
> > > > > a) SMMU level: I still believe, this patch has potential to overcome
> > > > > issue till finally driver's probe takeover.
> > > > > b) Device level: Even if something goes wrong. Driver/device should
> > > > > able to recover.
> > > > >
> > > > > > > Returned PCIe completion abort further leads to AER Errors from APEI
> > > > > > > Generic Hardware Error Source (GHES) with completion timeout.
> > > > > > > A network device hang is observed even after continuous
> > > > > > > reset/recovery from driver, Hence device is no more usable.
> > > > > >
> > > > > > The fact that the device is no longer usable is definitely a problem.
> > > > > > But in principle we *should* be able to recover from these errors.  If
> > > > > > we could recover and reliably use the device after the error, that
> > > > > > seems like it would be a more robust solution that having to add
> > > > > > special cases in every IOMMU driver.
> > > > > >
> > > > > > If you have details about this sort of error, I'd like to try to fix
> > > > > > it because we want to recover from that sort of error in normal
> > > > > > (non-crash) situations as well.
> > > > > >
> > > > > Completion abort case should be gracefully handled.  And device should
> > > > > always remain usable.
> > > > >
> > > > > There are 2 scenario which I am testing with Ethernet card PCIe-Intel
> > > > > 82576 Gigabit Network card.
> > > > >
> > > > > I)  Crash testing using kdump root file system: De-facto scenario
> > > > >     -  kdump file system does not have Ethernet driver
> > > > >     -  A lot of AER prints [1], making it impossible to work on shell
> > > > > of kdump root file system.
> > > >
> > > > In this case, I think report_error_detected() is deciding that because
> > > > the device has no driver, we can't do anything.  The flow is like
> > > > this:
> > > >
> > > >   aer_recover_work_func               # aer_recover_work
> > > >     kfifo_get(aer_recover_ring, entry)
> > > >     dev = pci_get_domain_bus_and_slot
> > > >     cper_print_aer(dev, ...)
> > > >       pci_err("AER: aer_status:")
> > > >       pci_err("AER:   [14] CmpltTO")
> > > >       pci_err("AER: aer_layer=")
> > > >     if (AER_NONFATAL)
> > > >       pcie_do_recovery(dev, pci_channel_io_normal)
> > > >         status = CAN_RECOVER
> > > >         pci_walk_bus(report_normal_detected)
> > > >           report_error_detected
> > > >             if (!dev->driver)
> > > >               vote = NO_AER_DRIVER
> > > >               pci_info("can't recover (no error_detected callback)")
> > > >             *result = merge_result(*, NO_AER_DRIVER)
> > > >             # always NO_AER_DRIVER
> > > >         status is now NO_AER_DRIVER
> > > >
> > > > So pcie_do_recovery() does not call .report_mmio_enabled() or .slot_reset(),
> > > > and status is not RECOVERED, so it skips .resume().
> > > >
> > > > I don't remember the history there, but if a device has no driver and
> > > > the device generates errors, it seems like we ought to be able to
> > > > reset it.
> > >
> > > But how to reset the device considering there is no driver.
> > > Hypothetically, this case should be taken care by PCIe subsystem to
> > > perform reset at PCIe level.
> >
> > I don't understand your question.  The PCI core (not the device
> > driver) already does the reset.  When pcie_do_recovery() calls
> > reset_link(), all devices on the other side of the link are reset.
> >
> > > > We should be able to field one (or a few) AER errors, reset the
> > > > device, and you should be able to use the shell in the kdump kernel.
> > > >
> > > here kdump shell is usable only problem is a "lot of AER Errors". One
> > > cannot see what they are typing.
> >
> > Right, that's what I expect.  If the PCI core resets the device, you
> > should get just a few AER errors, and they should stop after the
> > device is reset.
> >
> > > > >     -  Note kdump shell allows to use makedumpfile, vmcore-dmesg applications.
> > > > >
> > > > > II) Crash testing using default root file system: Specific case to
> > > > > test Ethernet driver in second kernel
> > > > >    -  Default root file system have Ethernet driver
> > > > >    -  AER error comes even before the driver probe starts.
> > > > >    -  Driver does reset Ethernet card as part of probe but no success.
> > > > >    -  AER also tries to recover. but no success.  [2]
> > > > >    -  I also tries to remove AER errors by using "pci=noaer" bootargs
> > > > > and commenting ghes_handle_aer() from GHES driver..
> > > > >           than different set of errors come which also never able to recover [3]
> > > > >
> > >
> > > Please suggest your view on this case. Here driver is preset.
> > > (driver/net/ethernet/intel/igb/igb_main.c)
> > > In this case AER errors starts even before driver probe starts.
> > > After probe, driver does the device reset with no success and even AER
> > > recovery does not work.
> >
> > This case should be the same as the one above.  If we can change the
> > PCI core so it can reset the device when there's no driver,  that would
> > apply to case I (where there will never be a driver) and to case II
> > (where there is no driver now, but a driver will probe the device
> > later).
> 
> Does this means change are required in PCI core.

Yes, I am suggesting that the PCI core does not do the right thing
here.

> I tried following changes in pcie_do_recovery() but it did not help.
> Same error as before.
> 
> -- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
>         pci_info(dev, "broadcast resume message\n");
>         pci_walk_bus(bus, report_resume, &status);
> @@ -203,7 +207,12 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>         return status;
> 
>  failed:
>         pci_uevent_ers(dev, PCI_ERS_RESULT_DISCONNECT);
> +       pci_reset_function(dev);
> +       pci_aer_clear_device_status(dev);
> +       pci_aer_clear_nonfatal_status(dev);

Did you confirm that this resets the devices in question (0000:09:00.0
and 0000:09:00.1, I think), and what reset mechanism this uses (FLR,
PM, etc)?

Case I is using APEI, and it looks like that can queue up 16 errors
(AER_RECOVER_RING_SIZE), so that queue could be completely full before
we even get a chance to reset the device.  But I would think that the
reset should *eventually* stop the errors, even though we might log
30+ of them first.

As an experiment, you could reduce AER_RECOVER_RING_SIZE to 1 or 2 and
see if it reduces the logging.

> > > Problem mentioned in case I and II goes away if do pci_reset_function
> > > during enumeration phase of kdump kernel.
> > > can we thought of doing pci_reset_function for all devices in kdump
> > > kernel or device specific quirk.
> > >
> > > --pk
> > >
> > >
> > > > > As per my understanding, possible solutions are
> > > > >  - Copy SMMU table i.e. this patch
> > > > > OR
> > > > >  - Doing pci_reset_function() during enumeration phase.
> > > > > I also tried clearing "M" bit using pci_clear_master during
> > > > > enumeration but it did not help. Because driver re-set M bit causing
> > > > > same AER error again.
> > > > >
> > > > >
> > > > > -pk
> > > > >
> > > > > ---------------------------------------------------------------------------------------------------------------------------
> > > > > [1] with bootargs having pci=noaer
> > > > >
> > > > > [   22.494648] {4}[Hardware Error]: Hardware error from APEI Generic
> > > > > Hardware Error Source: 1
> > > > > [   22.512773] {4}[Hardware Error]: event severity: recoverable
> > > > > [   22.518419] {4}[Hardware Error]:  Error 0, type: recoverable
> > > > > [   22.544804] {4}[Hardware Error]:   section_type: PCIe error
> > > > > [   22.550363] {4}[Hardware Error]:   port_type: 0, PCIe end point
> > > > > [   22.556268] {4}[Hardware Error]:   version: 3.0
> > > > > [   22.560785] {4}[Hardware Error]:   command: 0x0507, status: 0x4010
> > > > > [   22.576852] {4}[Hardware Error]:   device_id: 0000:09:00.1
> > > > > [   22.582323] {4}[Hardware Error]:   slot: 0
> > > > > [   22.586406] {4}[Hardware Error]:   secondary_bus: 0x00
> > > > > [   22.591530] {4}[Hardware Error]:   vendor_id: 0x8086, device_id: 0x10c9
> > > > > [   22.608900] {4}[Hardware Error]:   class_code: 000002
> > > > > [   22.613938] {4}[Hardware Error]:   serial number: 0xff1b4580, 0x90e2baff
> > > > > [   22.803534] pci 0000:09:00.1: AER: aer_status: 0x00004000,
> > > > > aer_mask: 0x00000000
> > > > > [   22.810838] pci 0000:09:00.1: AER:    [14] CmpltTO                (First)
> > > > > [   22.817613] pci 0000:09:00.1: AER: aer_layer=Transaction Layer,
> > > > > aer_agent=Requester ID
> > > > > [   22.847374] pci 0000:09:00.1: AER: aer_uncor_severity: 0x00062011
> > > > > [   22.866161] mpt3sas_cm0: 63 BIT PCI BUS DMA ADDRESSING SUPPORTED,
> > > > > total mem (8153768 kB)
> > > > > [   22.946178] pci 0000:09:00.0: AER: can't recover (no error_detected callback)
> > > > > [   22.995142] pci 0000:09:00.1: AER: can't recover (no error_detected callback)
> > > > > [   23.002300] pcieport 0000:00:09.0: AER: device recovery failed
> > > > > [   23.027607] pci 0000:09:00.1: AER: aer_status: 0x00004000,
> > > > > aer_mask: 0x00000000
> > > > > [   23.044109] pci 0000:09:00.1: AER:    [14] CmpltTO                (First)
> > > > > [   23.060713] pci 0000:09:00.1: AER: aer_layer=Transaction Layer,
> > > > > aer_agent=Requester ID
> > > > > [   23.068616] pci 0000:09:00.1: AER: aer_uncor_severity: 0x00062011
> > > > > [   23.122056] pci 0000:09:00.0: AER: can't recover (no error_detected callback)

<snip>

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec