Re: [PATCH v3 4/8] PCI: Add quirk to disable MSI-X support for Amazon's Annapurna Labs Root Port

[Chocron, Jonathan]

On Tue, 2019-08-20 at 16:25 +0100, Andrew Murray wrote:
> On Tue, Aug 20, 2019 at 02:52:30PM +0000, Chocron, Jonathan wrote:
> > On Mon, 2019-08-19 at 19:23 +0100, Andrew Murray wrote:
> > > On Tue, Jul 23, 2019 at 12:25:29PM +0300, Jonathan Chocron wrote:
> > > > The Root Port (identified by [1c36:0032]) doesn't support MSI-
> > > > X. On
> > > > some
> > > 
> > > Shouldn't this read [1c36:0031]?
> > > 
> > 
> > Indeed. Thanks for catching this.
> > 
> > > 
> > > > platforms it is configured to not advertise the capability at
> > > > all,
> > > > while
> > > > on others it (mistakenly) does. This causes a panic during
> > > > initialization by the pcieport driver, since it tries to
> > > > configure
> > > > the
> > > > MSI-X capability. Specifically, when trying to access the MSI-X
> > > > table
> > > > a "non-existing addr" exception occurs.
> > > > 
> > > > Example stacktrace snippet:
> > > > 
> > > > [    1.632363] SError Interrupt on CPU2, code 0xbf000000 --
> > > > SError
> > > > [    1.632364] CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.2.0-
> > > > rc1-
> > > > Jonny-14847-ge76f1d4a1828-dirty #33
> > > > [    1.632365] Hardware name: Annapurna Labs Alpine V3 EVP (DT)
> > > > [    1.632365] pstate: 80000005 (Nzcv daif -PAN -UAO)
> > > > [    1.632366] pc : __pci_enable_msix_range+0x4e4/0x608
> > > > [    1.632367] lr : __pci_enable_msix_range+0x498/0x608
> > > > [    1.632367] sp : ffffff80117db700
> > > > [    1.632368] x29: ffffff80117db700 x28: 0000000000000001
> > > > [    1.632370] x27: 0000000000000001 x26: 0000000000000000
> > > > [    1.632372] x25: ffffffd3e9d8c0b0 x24: 0000000000000000
> > > > [    1.632373] x23: 0000000000000000 x22: 0000000000000000
> > > > [    1.632375] x21: 0000000000000001 x20: 0000000000000000
> > > > [    1.632376] x19: ffffffd3e9d8c000 x18: ffffffffffffffff
> > > > [    1.632378] x17: 0000000000000000 x16: 0000000000000000
> > > > [    1.632379] x15: ffffff80116496c8 x14: ffffffd3e9844503
> > > > [    1.632380] x13: ffffffd3e9844502 x12: 0000000000000038
> > > > [    1.632382] x11: ffffffffffffff00 x10: 0000000000000040
> > > > [    1.632384] x9 : ffffff801165e270 x8 : ffffff801165e268
> > > > [    1.632385] x7 : 0000000000000002 x6 : 00000000000000b2
> > > > [    1.632387] x5 : ffffffd3e9d8c2c0 x4 : 0000000000000000
> > > > [    1.632388] x3 : 0000000000000000 x2 : 0000000000000000
> > > > [    1.632390] x1 : 0000000000000000 x0 : ffffffd3e9844680
> > > > [    1.632392] Kernel panic - not syncing: Asynchronous SError
> > > > Interrupt
> > > > [    1.632393] CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.2.0-
> > > > rc1-
> > > > Jonny-14847-ge76f1d4a1828-dirty #33
> > > > [    1.632394] Hardware name: Annapurna Labs Alpine V3 EVP (DT)
> > > > [    1.632394] Call trace:
> > > > [    1.632395]  dump_backtrace+0x0/0x140
> > > > [    1.632395]  show_stack+0x14/0x20
> > > > [    1.632396]  dump_stack+0xa8/0xcc
> > > > [    1.632396]  panic+0x140/0x334
> > > > [    1.632397]  nmi_panic+0x6c/0x70
> > > > [    1.632398]  arm64_serror_panic+0x74/0x88
> > > > [    1.632398]  __pte_error+0x0/0x28
> > > > [    1.632399]  el1_error+0x84/0xf8
> > > > [    1.632400]  __pci_enable_msix_range+0x4e4/0x608
> > > > [    1.632400]  pci_alloc_irq_vectors_affinity+0xdc/0x150
> > > > [    1.632401]  pcie_port_device_register+0x2b8/0x4e0
> > > > [    1.632402]  pcie_portdrv_probe+0x34/0xf0
> > > > 
> > > > Signed-off-by: Jonathan Chocron <jonnyc@xxxxxxxxxx>
> > > > Reviewed-by: Gustavo Pimentel <gustavo.pimentel@xxxxxxxxxxxx>
> > > > ---
> > > >  drivers/pci/quirks.c | 15 +++++++++++++++
> > > >  1 file changed, 15 insertions(+)
> > > > 
> > > > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > > > index 23672680dba7..11f843aa96b3 100644
> > > > --- a/drivers/pci/quirks.c
> > > > +++ b/drivers/pci/quirks.c
> > > > @@ -2925,6 +2925,21 @@
> > > > DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_ATTANSIC, 0x10a1,
> > > >  			quirk_msi_intx_disable_qca_bug);
> > > >  DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_ATTANSIC, 0xe091,
> > > >  			quirk_msi_intx_disable_qca_bug);
> > > > +
> > > > +/*
> > > > + * Amazon's Annapurna Labs 1c36:0031 Root Ports don't support
> > > > MSI-
> > > > X, so it
> > > > + * should be disabled on platforms where the device
> > > > (mistakenly)
> > > > advertises it.
> > > > + *
> > > > + * The 0031 device id is reused for other non Root Port device
> > > > types,
> > > > + * therefore the quirk is registered for the
> > > > PCI_CLASS_BRIDGE_PCI
> > > > class.
> > > > + */
> > > > +static void quirk_al_msi_disable(struct pci_dev *dev)
> > > > +{
> > > > +	dev->no_msi = 1;
> > > > +	pci_warn(dev, "Disabling MSI-X\n");
> > > 
> > > This will disable both MSI and MSI-X support - is this really the
> > > intention
> > > here? Do the root ports support MSI and legacy, or just legacy?
> > > 
> > 
> > The HW should support MSI, but we currently don't have a use case
> > for
> > it so it hasn't been tested and therefore we are okay with
> > disabling
> > it.
> 
> OK - then the commit message and comment (for quirk_al_msi_disable)
> should
> probably be updated to reflect this. 

If you mean that we should explicitly state that MSI is possibly
supported then I don't think it is very relevant here. If we decide to
test and enable it in the future, then the new quirk (which would only
disable MSI-x) would reflect the fact that MSI works. Sounds ok?

> Especially given that the device id
> may be used on other device types - implying that a use-case for this
> may later arise.
> 
Not sure I understood that last line. This patch is relevant only for
the BRIDGE class 0x0031 device. The other device types, which (sadly)
happen to re-use the dev_id, have are totally different and shouldn't
be mixed in here.

> > 
> > For future knowledge, how can just MSI-X be disabled?
> > I see that in pcie_port_enable_irq_vec(), the pcieport driver calls
> > pci_alloc_irq_vectors() with PCI_IRQ_MSIX | PCI_IRQ_MSI. And
> > internally, both __pci_enable_msix_range() and
> > __pci_enable_msi_range()
> > use pci_msi_supported() which doesn't differentiate between MSI and
> > MSI-x.
> 
> The documentation [1] would suggest that once upon a time
> pci_disable_msix
> was used - but now should let pci_alloc_irq_vectors cap the max
> number
> of vectors. However in your case it's the PCIe port driver that is
> attempting
> to allocate MSI-X's and so the solution isn't an obvious one.
> 
> Setting dev->msix_enabled to false (i.e. through pci_disable_msix)
> would
> result in an un-necessary WARN_ON_ONCE. 

Per my understanding, it seems that dev->msix_enabled indicates if the
MSI-X capability has already been enabled or not, and not as an
indication if it is supported by the device. If that is the case, then
not sure pci_disable_msix() would result in the desired effect.

> I think you'd need to ensure
> devi->msix_cap is NULL (which makes sense as your hardware shouldn't
> be
> exposing this capability).
> 
> I guess the right way of achieving this would be through a quirk,
> though you'd
> be the first to do this and you'd have to ensure the quirk runs
> before
> anyone tests for msix_cap.
> 
> That's my view, though others may have different suggestions.
> 
I think that maybe a dev->no_msix field should be added and then a
corresponding pci_msix_supported() function as well. I'd be glad to
take it offline or on a dedicated thread, but it shouldn't block this
patchset.

> [1] Documentation/PCI/msi-howto.rst
> 
> Thanks,
> 
> Andrew Murray
> 
> > 
> > > Thanks,
> > > 
> > > Andrew Murray
> > > 
> > > > +}
> > > > +DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_AMAZON_ANNAPURNA_L
> > > > ABS,
> > > > 0x0031,
> > > > +			      PCI_CLASS_BRIDGE_PCI, 8,
> > > > quirk_al_msi_disable);
> > > >  #endif /* CONFIG_PCI_MSI */
> > > >  
> > > >  /*
> > > > -- 
> > > > 2.17.1
> > > >