Re: [PATCH] PCI: controller: Restore PCI_REASSIGN_ALL_BUS when PCI_PROBE_ONLY is enabled

From: Manivannan Sadhasivam
Date: Wed Mar 05 2025 - 01:06:47 EST

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On Fri, Feb 28, 2025 at 07:58:10PM +0800, Bo Sun wrote:
> On 2/15/25 1:00 AM, Manivannan Sadhasivam wrote:
> > CAUTION: This email comes from a non Wind River email account!
> > Do not click links or open attachments unless you recognize the sender and know the content is safe.
> >
> > On Wed, Feb 12, 2025 at 03:07:56PM +0800, Bo Sun wrote:
> > > On 2/10/25 18:37, Manivannan Sadhasivam wrote:
> > > > CAUTION: This email comes from a non Wind River email account!
> > > > Do not click links or open attachments unless you recognize the sender and know the content is safe.
> > > >
> > > > On Fri, Jan 17, 2025 at 04:24:14PM +0800, Bo Sun wrote:
> > > > > On our Marvell OCTEON CN96XX board, we observed the following panic on
> > > > > the latest kernel:
> > > > > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000080
> > > > > Mem abort info:
> > > > > ESR = 0x0000000096000005
> > > > > EC = 0x25: DABT (current EL), IL = 32 bits
> > > > > SET = 0, FnV = 0
> > > > > EA = 0, S1PTW = 0
> > > > > FSC = 0x05: level 1 translation fault
> > > > > Data abort info:
> > > > > ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
> > > > > CM = 0, WnR = 0, TnD = 0, TagAccess = 0
> > > > > GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
> > > > > [0000000000000080] user address but active_mm is swapper
> > > > > Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
> > > > > Modules linked in:
> > > > > CPU: 9 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.13.0-rc7-00149-g9bffa1ad25b8 #1
> > > > > Hardware name: Marvell OcteonTX CN96XX board (DT)
> > > > > pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> > > > > pc : of_pci_add_properties+0x278/0x4c8
> > > > > lr : of_pci_add_properties+0x258/0x4c8
> > > > > sp : ffff8000822ef9b0
> > > > > x29: ffff8000822ef9b0 x28: ffff000106dd8000 x27: ffff800081bc3b30
> > > > > x26: ffff800081540118 x25: ffff8000813d2be0 x24: 0000000000000000
> > > > > x23: ffff00010528a800 x22: ffff000107c50000 x21: ffff0001039c2630
> > > > > x20: ffff0001039c2630 x19: 0000000000000000 x18: ffffffffffffffff
> > > > > x17: 00000000a49c1b85 x16: 0000000084c07b58 x15: ffff000103a10f98
> > > > > x14: ffffffffffffffff x13: ffff000103a10f96 x12: 0000000000000003
> > > > > x11: 0101010101010101 x10: 000000000000002c x9 : ffff800080ca7acc
> > > > > x8 : ffff0001038fd900 x7 : 0000000000000000 x6 : 0000000000696370
> > > > > x5 : 0000000000000000 x4 : 0000000000000002 x3 : ffff8000822efa40
> > > > > x2 : ffff800081341000 x1 : ffff000107c50000 x0 : 0000000000000000
> > > > > Call trace:
> > > > > of_pci_add_properties+0x278/0x4c8 (P)
> > > > > of_pci_make_dev_node+0xe0/0x158
> > > > > pci_bus_add_device+0x158/0x210
> > > > > pci_bus_add_devices+0x40/0x98
> > > > > pci_host_probe+0x94/0x118
> > > > > pci_host_common_probe+0x120/0x1a0
> > > > > platform_probe+0x70/0xf0
> > > > > really_probe+0xb4/0x2a8
> > > > > __driver_probe_device+0x80/0x140
> > > > > driver_probe_device+0x48/0x170
> > > > > __driver_attach+0x9c/0x1b0
> > > > > bus_for_each_dev+0x7c/0xe8
> > > > > driver_attach+0x2c/0x40
> > > > > bus_add_driver+0xec/0x218
> > > > > driver_register+0x68/0x138
> > > > > __platform_driver_register+0x2c/0x40
> > > > > gen_pci_driver_init+0x24/0x38
> > > > > do_one_initcall+0x4c/0x278
> > > > > kernel_init_freeable+0x1f4/0x3d0
> > > > > kernel_init+0x28/0x1f0
> > > > > ret_from_fork+0x10/0x20
> > > > > Code: aa1603e1 f0005522 d2800044 91000042 (f94040a0)
> > > > >
> > > > > This regression was introduced by commit 7246a4520b4b ("PCI: Use
> > > > > preserve_config in place of pci_flags"). On our board, the 002:00:07.0
> > > > > bridge is misconfigured by the bootloader. Both its secondary and
> > > > > subordinate bus numbers are initialized to 0, while its fixed secondary
> > > > > bus number is set to 8.
> > > >
> > > > What do you mean by 'fixed secondary bus number'?
> > > >
> > >
> > > The 'fixed secondary bus number' refers to the value returned by the
> > > function pci_ea_fixed_busnrs(), which reads the fixed Secondary and
> > > Subordinate bus numbers from the EA (Extended Attributes) capability, if
> > > present.
> >
> > Thanks! It'd be good to mention the EA capability.
> >
> > > In the code at drivers/pci/probe.c, line 1439, we have the
> > > following:
> > >
> > > /* Read bus numbers from EA Capability (if present) */
> > > fixed_buses = pci_ea_fixed_busnrs(dev, &fixed_sec, &fixed_sub);
> > > if (fixed_buses)
> > > next_busnr = fixed_sec;
> > > else
> > > next_busnr = max + 1;
> > >
> > > > > However, bus number 8 is also assigned to another
> > > > > bridge (0002:00:0f.0). Although this is a bootloader issue, before the
> > > > > change in commit 7246a4520b4b, the PCI_REASSIGN_ALL_BUS flag was
> > > > > set by default when PCI_PROBE_ONLY was enabled, ensuing that all the
> > > > > bus number for these bridges were reassigned, avoiding any conflicts.
> > > > >
> > > >
> > > > Isn't the opposite? PCI_REASSIGN_ALL_BUS was only added if the PCI_PROBE_ONLY
> > > > flag was not set:
> > > >
> > > > /* Do not reassign resources if probe only */
> > > > if (!pci_has_flag(PCI_PROBE_ONLY))
> > > > pci_add_flags(PCI_REASSIGN_ALL_BUS);
> > > >
> > >
> > > Yes, you are correct. It’s a typo; it should be "when PCI_PROBE_ONLY was not
> > > enabled." I will fix this in v2.
> > >
> > > >
> > > > > After the change introduced in commit 7246a4520b4b, the bus numbers
> > > > > assigned by the bootloader are reused by all other bridges, except
> > > > > the misconfigured 002:00:07.0 bridge. The kernel attempt to reconfigure
> > > > > 002:00:07.0 by reusing the fixed secondary bus number 8 assigned by
> > > > > bootloader. However, since a pci_bus has already been allocated for
> > > > > bus 8 due to the probe of 0002:00:0f.0, no new pci_bus allocated for
> > > > > 002:00:07.0.
> > > >
> > > > How come 0002:00:0f.0 is enumerated before 0002:00:07.0 in a depth first manner?
> > > >
> > >
> > > The device 0002:00:07.0 is actually enumerated before 0002:00:0f.0, but it
> > > appears misconfigured. The kernel attempts to reconfigure it during
> > > initialization, which is where the issue arises.
> > >
> >
> > Ok, thanks for the clarification. I think the bug is in this part of the code:
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/probe.c#n1451
> >
> > It just reuses the fixed bus number even if the bus already exists, which is
> > wrong. I think this should be fixed by evaluating the bus number read from EA
> > capability as below:
> >
> > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> > index b6536ed599c3..097e2a01faae 100644
> > --- a/drivers/pci/probe.c
> > +++ b/drivers/pci/probe.c
> > @@ -1438,10 +1438,21 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
> >
> > /* Read bus numbers from EA Capability (if present) */
> > fixed_buses = pci_ea_fixed_busnrs(dev, &fixed_sec, &fixed_sub);
> > - if (fixed_buses)
> > - next_busnr = fixed_sec;
> > - else
> > + if (fixed_buses) {
> > + /*
> > + * If the fixed bus number is already taken, use the
> > + * next available bus number. This can happen if the
> > + * bootloader has assigned a wrong bus number in EA
> > + * capability of the bridge.
> > + */
> > + child = pci_find_bus(pci_domain_nr(bus), fixed_sec);
> > + if (child)
> > + next_busnr = max + 1;
> > + else
> > + next_busnr = fixed_sec;
> > + } else {
> > next_busnr = max + 1;
> > + }
> >
> > /*
> > * Prevent assigning a bus number that already exists.
>
> You proposed solution doesn't work on our Marvell OCTEON CN96XX board.
>
> When probing the bus 0002:00, the bus number preset by the bootloader for
> the bridges under this bus start with 0xf9. Before configure of
> 0002:00:07.0, the 'max' bus number has already reached 0xff. With your
> proposed fix, the next_busnr is set to (0xff + 1), which evaluate to 0x100.
> This results in a 0 being assigned to the secondary bus number of
> 0002:00:07.0 bridge, causing a recursive bus probe.
>

Oops. This is turning out to be too much of a problem.

> For reference, you can take a look at the code in probe.c and the
> corresponding log.
>
> pci_read_config_dword(dev, PCI_PRIMARY_BUS, &buses);
>
> primary = buses & 0xFF;
>
> secondary = (buses >> 8) & 0xFF;
>
> subordinate = (buses >> 16) & 0xFF;
>
>
> pci_dbg(dev, "scanning [bus %02x-%02x] behind bridge, pass %d\n",
>
> secondary, subordinate, pass);
>
> pci_bus 0002:00: fixups for bus
> pci 0002:00:00.0: scanning [bus f9-f9] behind bridge, pass 0
> pci_bus 0002:f9: scanning bus
> pci_bus 0002:f9: fixups for bus
> pci_bus 0002:f9: bus scan returning with max=f9
> ...
> pci 0002:00:06.0: scanning [bus ff-ff] behind bridge, pass 0
> pci_bus 0002:ff: scanning bus
> pci_bus 0002:ff: fixups for bus
> pci_bus 0002:ff: bus scan returning with max=ff
> pci 0002:00:07.0: scanning [bus 00-00] behind bridge, pass 0
> pci 0002:00:07.0: bridge configuration invalid ([bus 00-00]), reconfiguring
> ...
> Kernel panic - not syncing: kernel stack overflow
> CPU: 12 UID: 0 PID: 1 Comm: swapper/0 Not tainted
> 6.14.0-rc4-00091-ga58485af8826 #16
> Hardware name: Marvell OcteonTX CN96XX board (DT)
> Call trace:
> show_stack+0x20/0x38 (C)
> dump_stack_lvl+0x38/0x90
> dump_stack+0x18/0x28
> panic+0x3ac/0x3c8
> nmi_panic+0x48/0xa0
> panic_bad_stack+0x118/0x140
> handle_bad_stack+0x34/0x38
> __bad_stack+0x80/0x88
> format_decode+0x4/0x2e8 (P)
> va_format.constprop.0+0x74/0x130
> pointer+0x204/0x4f8
> vsnprintf+0x2c4/0x5a0
> vscnprintf+0x34/0x58
> printk_sprint+0x48/0x170
> vprintk_store+0x2d0/0x478
> vprintk_emit+0xb0/0x2b0
> dev_vprintk_emit+0xe0/0x1b0
> dev_printk_emit+0x60/0x90
> __dev_printk+0x44/0x98
> _dev_printk+0x5c/0x90
> pci_scan_child_bus_extend+0x5c/0x2c0
> pci_scan_bridge_extend+0x16c/0x630
> pci_scan_child_bus_extend+0xfc/0x2c0
> pci_scan_bridge_extend+0x320/0x630
> pci_scan_child_bus_extend+0x1b0/0x2c0
> pci_scan_bridge_extend+0x320/0x630
>
> So, I propose the following solution as a workaround to handle these edge
> cases.
>
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 82b21e34c545..af8efebc7e7d 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -6181,6 +6181,13 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x1536,
> rom_bar_overlap_defect);
> DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x1537,
> rom_bar_overlap_defect);
> DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x1538,
> rom_bar_overlap_defect);
>
> +static void quirk_marvell_cn96xx_cn10xxx_reassign_all_busnr(struct pci_dev
> *dev)
> +{
> + if (!pci_has_flag(PCI_PROBE_ONLY))
> + pci_add_flags(PCI_REASSIGN_ALL_BUS);
> +}
> +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_CAVIUM, 0xa002,
> quirk_marvell_cn96xx_cn10xxx_reassign_all_busnr);
> +

LGTM. Please add a comment about this quirk too.

- Mani

--
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