Re: [PATCH v5 4/7] PCI: Add quirk to disable MSI-X support for Amazon's Annapurna Labs Root Port

["Chocron, Jonathan" <jonnyc@amazon.com>]

On Sat, 2019-09-07 at 11:55 -0500, Bjorn Helgaas wrote:
> s/Add quirk to disable/Disable/ in subject
> 
> On Thu, Sep 05, 2019 at 05:00:18PM +0300, Jonathan Chocron wrote:
> > The Root Port (identified by [1c36:0031]) doesn't support MSI-X. On
> > some
> > 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.
> 
> MSI-X configuration is all in memory space (not config space), so I
> guess this device has a BAR (maybe more) and the MSI-X table access
> would be to something in that BAR?  Or is there junk in the
> capability
> so we try to access something completely outside the BAR?  [I wonder
> if
> it'd be worth adding some validation to make sure the Table and PBA
> areas are contained in the BAR?]
> 
There is no actual memory allocated for the MSI-X table behind the BAR,
so it attempts to access non existing regs, resulting in the SError.

> The reason I'm curious about all this is because on the PCI side this
> is probably an Unsupported Request or similar error, and on *most*
> platforms, this does not cause a panic.  If it was a read, the read
> usually gets ~0 data, and writes are dropped.
> 
I'm not entirely sure how this is implemented in the HW (i.e. accessing
the Host controller's memory space), but I assume that an AXI error
returns, which translates to the Serror. I can verify with our HW
engineers if you think it is blocking.

> So my concern is that we'll avoid this panic by disabling MSI, but
> we'll see other panics in other places.
> 
> > Example stacktrace snippet:
> 
> [Remove the timestamps since they're not really relevant and indent
> the quote a couple spaces]
> 
Ack.

> > [    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
> > 
> > Notice that this quirk also disables MSI (which may work, but
> > hasn't
> > been tested nor has a current use case), since currently there is
> > no
> > standard way to disable only MSI-X.
> > 
> > Signed-off-by: Jonathan Chocron <jonnyc@amazon.com>
> > Reviewed-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
> > Reviewed-by: Andrew Murray <andrew.murray@arm.com>
> > ---
> >  drivers/pci/quirks.c | 18 ++++++++++++++++++
> >  1 file changed, 18 insertions(+)
> > 
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index 8fe765592943..5a8ea5fdeae7 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -2977,6 +2977,24 @@
> > 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.
> > + *
> > + * Notice that this quirk also disables MSI (which may work, but
> > hasn't been
> > + * tested), since currently there is no standard way to disable
> > only MSI-X.
> > + *
> > + * 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/MSI-X\n");
> > +}
> > +DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_AMAZON_ANNAPURNA_LABS,
> > 0x0031,
> > +			      PCI_CLASS_BRIDGE_PCI, 8,
> > quirk_al_msi_disable);
> >  #endif /* CONFIG_PCI_MSI */
> >  
> >  /*
> > -- 
> > 2.17.1
> >