RE: [PATCH 1/1] iommu/vt-d: Fix WARN_ON in iommu probe path

[Tian, Kevin]

> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Thursday, April 11, 2024 10:48 AM
> 
> On 4/7/24 9:14 AM, Lu Baolu wrote:
> > Commit 1a75cc710b95 ("iommu/vt-d: Use rbtree to track iommu probed
> > devices") adds all devices probed by the iommu driver in a rbtree
> > indexed by the source ID of each device. It assumes that each device
> > has a unique source ID. This assumption is incorrect and the VT-d
> > spec doesn't state this requirement either.
> >
> > The reason for using a rbtree to track devices is to look up the device
> > with PCI bus and devfunc in the paths of handling ATS invalidation time
> > out error and the PRI I/O page faults. Both are PCI ATS feature related.
> >
> > Only track the devices that have PCI ATS capabilities in the rbtree to
> > avoid unnecessary WARN_ON in the iommu probe path. Otherwise, on
> some
> > platforms below kernel splat will be displayed and the iommu probe results
> > in failure.
> >
> >   WARNING: CPU: 3 PID: 166 at drivers/iommu/intel/iommu.c:158
> intel_iommu_probe_device+0x319/0xd90
> >   Call Trace:
> >    <TASK>
> >    ? __warn+0x7e/0x180
> >    ? intel_iommu_probe_device+0x319/0xd90
> >    ? report_bug+0x1f8/0x200
> >    ? handle_bug+0x3c/0x70
> >    ? exc_invalid_op+0x18/0x70
> >    ? asm_exc_invalid_op+0x1a/0x20
> >    ? intel_iommu_probe_device+0x319/0xd90
> >    ? debug_mutex_init+0x37/0x50
> >    __iommu_probe_device+0xf2/0x4f0
> >    iommu_probe_device+0x22/0x70
> >    iommu_bus_notifier+0x1e/0x40
> >    notifier_call_chain+0x46/0x150
> >    blocking_notifier_call_chain+0x42/0x60
> >    bus_notify+0x2f/0x50
> >    device_add+0x5ed/0x7e0
> >    platform_device_add+0xf5/0x240
> >    mfd_add_devices+0x3f9/0x500
> >    ? preempt_count_add+0x4c/0xa0
> >    ? up_write+0xa2/0x1b0
> >    ? __debugfs_create_file+0xe3/0x150
> >    intel_lpss_probe+0x49f/0x5b0
> >    ? pci_conf1_write+0xa3/0xf0
> >    intel_lpss_pci_probe+0xcf/0x110 [intel_lpss_pci]
> >    pci_device_probe+0x95/0x120
> >    really_probe+0xd9/0x370
> >    ? __pfx___driver_attach+0x10/0x10
> >    __driver_probe_device+0x73/0x150
> >    driver_probe_device+0x19/0xa0
> >    __driver_attach+0xb6/0x180
> >    ? __pfx___driver_attach+0x10/0x10
> >    bus_for_each_dev+0x77/0xd0
> >    bus_add_driver+0x114/0x210
> >    driver_register+0x5b/0x110
> >    ? __pfx_intel_lpss_pci_driver_init+0x10/0x10 [intel_lpss_pci]
> >    do_one_initcall+0x57/0x2b0
> >    ? kmalloc_trace+0x21e/0x280
> >    ? do_init_module+0x1e/0x210
> >    do_init_module+0x5f/0x210
> >    load_module+0x1d37/0x1fc0
> >    ? init_module_from_file+0x86/0xd0
> >    init_module_from_file+0x86/0xd0
> >    idempotent_init_module+0x17c/0x230
> >    __x64_sys_finit_module+0x56/0xb0
> >    do_syscall_64+0x6e/0x140
> >    entry_SYSCALL_64_after_hwframe+0x71/0x79
> >
> > Fixes: 1a75cc710b95 ("iommu/vt-d: Use rbtree to track iommu probed
> devices")
> > Signed-off-by: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/intel/iommu.c | 11 +++++++----
> >   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> This patch closes a boot bug described here.
> 
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/10689
> 
> I will queue it for v6.9-rc if no objection.
> 

let's do it. the issue which I raised is rare and can be tackled when
it arises.

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>