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Date:   Thu, 4 Feb 2021 17:27:58 -0600
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc:     Bjorn Helgaas <bhelgaas@google.com>,
        Russell Currey <ruscur@russell.cc>,
        Oliver O'Halloran <oohall@gmail.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Lalithambika Krishnakumar <lalithambika.krishnakumar@intel.com>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Joerg Roedel <jroedel@suse.de>,
        Alex Williamson <alex.williamson@redhat.com>,
        "open list:PCI ENHANCED ERROR HANDLING (EEH) FOR POWERPC" 
        <linuxppc-dev@lists.ozlabs.org>,
        "open list:PCI SUBSYSTEM" <linux-pci@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] PCI/AER: Disable AER interrupt during suspend
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[+cc Alex]

On Thu, Jan 28, 2021 at 12:09:37PM +0800, Kai-Heng Feng wrote:
> On Thu, Jan 28, 2021 at 4:51 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > On Thu, Jan 28, 2021 at 01:31:00AM +0800, Kai-Heng Feng wrote:
> > > Commit 50310600ebda ("iommu/vt-d: Enable PCI ACS for platform opt in
> > > hint") enables ACS, and some platforms lose its NVMe after resume from
> > > firmware:
> > > [   50.947816] pcieport 0000:00:1b.0: DPC: containment event, status:0x1f01 source:0x0000
> > > [   50.947817] pcieport 0000:00:1b.0: DPC: unmasked uncorrectable error detected
> > > [   50.947829] pcieport 0000:00:1b.0: PCIe Bus Error: severity=Uncorrected (Non-Fatal), type=Transaction Layer, (Receiver ID)
> > > [   50.947830] pcieport 0000:00:1b.0:   device [8086:06ac] error status/mask=00200000/00010000
> > > [   50.947831] pcieport 0000:00:1b.0:    [21] ACSViol                (First)
> > > [   50.947841] pcieport 0000:00:1b.0: AER: broadcast error_detected message
> > > [   50.947843] nvme nvme0: frozen state error detected, reset controller
> > >
> > > It happens right after ACS gets enabled during resume.
> > >
> > > To prevent that from happening, disable AER interrupt and enable it on
> > > system suspend and resume, respectively.
> >
> > Lots of questions here.  Maybe this is what we'll end up doing, but I
> > am curious about why the error is reported in the first place.
> >
> > Is this a consequence of the link going down and back up?
> 
> Could be. From the observations, it only happens when firmware suspend
> (S3) is used.
> Maybe it happens when it's gets powered up, but I don't have equipment
> to debug at hardware level.
> 
> If we use non-firmware suspend method, enabling ACS after resume won't
> trip AER and DPC.
> 
> > Is it consequence of the device doing a DMA when it shouldn't?
> 
> If it's doing DMA while suspending, the same error should also happen
> after NVMe is suspended and before PCIe port suspending.
> Furthermore, if non-firmware suspend method is used, there's so such
> issue, so less likely to be any DMA operation.
> 
> > Are we doing something in the wrong order during suspend?  Or maybe
> > resume, since I assume the error is reported during resume?
> 
> Yes the error is reported during resume. The suspend/resume order
> seems fine as non-firmware suspend doesn't have this issue.

I really feel like we need a better understanding of what's going on
here.  Disabling the AER interrupt is like closing our eyes and
pretending that because we don't see it, it didn't happen.

An ACS error is triggered by a DMA, right?  I'm assuming an MMIO
access from the CPU wouldn't trigger this error.  And it sounds like
the error is triggered before we even start running the driver after
resume.

If we're powering up an NVMe device from D3cold and it DMAs before the
driver touches it, something would be seriously broken.  I doubt
that's what's happening.  Maybe a device could resume some previously
programmed DMA after powering up from D3hot.

Or maybe the error occurred on suspend, like if the device wasn't
quiesced or something, but we didn't notice it until resume?  The 
AER error status bits are RW1CS, which means they can be preserved
across hot/warm/cold resets.

Can you instrument the code to see whether the AER error status bit is
set before enabling ACS?  I'm not sure that merely enabling ACS (I
assume you mean pci_std_enable_acs(), where we write PCI_ACS_CTRL)
should cause an interrupt for a previously-logged error.  I suspect
that could happen when enabling *AER*, but I wouldn't think it would
happen when enabling *ACS*.

Does this error happen on multiple machines from different vendors?
Wondering if it could be a BIOS issue, e.g., BIOS not cleaning up
after it did something to cause an error.

> > If we *do* take the error, why doesn't DPC recovery work?
> 
> It works for the root port, but not for the NVMe drive:
> [   50.947816] pcieport 0000:00:1b.0: DPC: containment event,
> status:0x1f01 source:0x0000
> [   50.947817] pcieport 0000:00:1b.0: DPC: unmasked uncorrectable error detected
> [   50.947829] pcieport 0000:00:1b.0: PCIe Bus Error:
> severity=Uncorrected (Non-Fatal), type=Transaction Layer, (Receiver
> ID)
> [   50.947830] pcieport 0000:00:1b.0:   device [8086:06ac] error
> status/mask=00200000/00010000
> [   50.947831] pcieport 0000:00:1b.0:    [21] ACSViol                (First)
> [   50.947841] pcieport 0000:00:1b.0: AER: broadcast error_detected message
> [   50.947843] nvme nvme0: frozen state error detected, reset controller
> [   50.948400] ACPI: EC: event unblocked
> [   50.948432] xhci_hcd 0000:00:14.0: PME# disabled
> [   50.948444] xhci_hcd 0000:00:14.0: enabling bus mastering
> [   50.949056] pcieport 0000:00:1b.0: PME# disabled
> [   50.949068] pcieport 0000:00:1c.0: PME# disabled
> [   50.949416] e1000e 0000:00:1f.6: PME# disabled
> [   50.949463] e1000e 0000:00:1f.6: enabling bus mastering
> [   50.951606] sd 0:0:0:0: [sda] Starting disk
> [   50.951610] nvme 0000:01:00.0: can't change power state from D3hot
> to D0 (config space inaccessible)
> [   50.951730] nvme nvme0: Removing after probe failure status: -19
> [   50.952360] nvme nvme0: failed to set APST feature (-19)
> [   50.971136] snd_hda_intel 0000:00:1f.3: PME# disabled
> [   51.089330] pcieport 0000:00:1b.0: AER: broadcast resume message
> [   51.089345] pcieport 0000:00:1b.0: AER: device recovery successful
> 
> But I think why recovery doesn't work for NVMe is for another discussion...
> 
> Kai-Heng
> 
> >
> > > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=209149
> > > Fixes: 50310600ebda ("iommu/vt-d: Enable PCI ACS for platform opt in hint")
> > > Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> > > ---
> > >  drivers/pci/pcie/aer.c | 18 ++++++++++++++++++
> > >  1 file changed, 18 insertions(+)
> > >
> > > diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
> > > index 77b0f2c45bc0..0e9a85530ae6 100644
> > > --- a/drivers/pci/pcie/aer.c
> > > +++ b/drivers/pci/pcie/aer.c
> > > @@ -1365,6 +1365,22 @@ static int aer_probe(struct pcie_device *dev)
> > >       return 0;
> > >  }
> > >
> > > +static int aer_suspend(struct pcie_device *dev)
> > > +{
> > > +     struct aer_rpc *rpc = get_service_data(dev);
> > > +
> > > +     aer_disable_rootport(rpc);
> > > +     return 0;
> > > +}
> > > +
> > > +static int aer_resume(struct pcie_device *dev)
> > > +{
> > > +     struct aer_rpc *rpc = get_service_data(dev);
> > > +
> > > +     aer_enable_rootport(rpc);
> > > +     return 0;
> > > +}
> > > +
> > >  /**
> > >   * aer_root_reset - reset Root Port hierarchy, RCEC, or RCiEP
> > >   * @dev: pointer to Root Port, RCEC, or RCiEP
> > > @@ -1437,6 +1453,8 @@ static struct pcie_port_service_driver aerdriver = {
> > >       .service        = PCIE_PORT_SERVICE_AER,
> > >
> > >       .probe          = aer_probe,
> > > +     .suspend        = aer_suspend,
> > > +     .resume         = aer_resume,
> > >       .remove         = aer_remove,
> > >  };
> > >
> > > --
> > > 2.29.2
> > >