Re: [PATCH v2 0/2] Fix get a wrong pci host bridge in cxl_setup_parent_dport()

["Li, Ming4" <ming4.li@intel.com>]

On 8/10/2024 5:36 AM, Dan Williams wrote:
> Li Ming wrote:
>> The cxl_test unit test environment on qemu always hit below call trace
>> with KASAN enabled:
>>
>>  BUG: KASAN: slab-out-of-bounds in cxl_setup_parent_dport+0x480/0x530 [cxl_core]
>>  Read of size 1 at addr ff110000676014f8 by task (udev-worker)/676[   24.424403] CPU: 2 PID: 676 Comm: (udev-worker) Tainted: G           O     N 6.10.0-qemucxl #1
>>  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20240214-2.el9 02/14/2024
>>  Call Trace:
>>   <TASK>
>>   dump_stack_lvl+0xea/0x150
>>   print_report+0xce/0x610
>>   ? kasan_complete_mode_report_info+0x40/0x200
>>   kasan_report+0xcc/0x110
>>   __asan_report_load1_noabort+0x18/0x20
>>   cxl_setup_parent_dport+0x480/0x530 [cxl_core]
>>   cxl_mem_probe+0x49b/0xaa0 [cxl_mem]
>>
>> The root cause is that a wrong host bridge was gotten from
>> dport->dport_dev in cxl_setup_parent_dport(). In
>> cxl_setup_parent_dport(), it always calls
>> to_pci_host_bridge(dport->dport_dev) to get a pci_host_bridge structure.
>> There are two issues in the implementation:
>>
>> * to_pci_host_bridge(dport->dport_dev) should be used only for RCH
>>   cases, dport->dport_dev points to a pci device rather than a pci host
>>   bridge in VH cases. The solution is checking if dport is in RCH mode
>>   then calling to_pci_host_bridge().
>>   (Patch 1)
>>
>> * In cxl_test unit test environment, cxl_test will create a emulated CXL
>>   topology with emulated dports, the dport_dev of a emulated dport
>>   points to a platform device. to_pci_host_bridge(dport->dport_dev) also
>>   gets a wrong pci host bridge in the case. The solution is implementing
>>   a new wrap function called __wrap_cxl_setup_parent_dport() on cxl_test
>>   side, the function will filter all emulated dports, make sure only
>>   real dports can be handled by cxl_setup_parent_dport().
>>   (Patch 2)
>>
>> v1 link: https://lore.kernel.org/linux-cxl/ZrHR+0w3bwM1Ik8h@xpf.sh.intel.com/T/#med6200e54ec12f09fdcc04571516adda261c9561
>>
>> v2:
>> - Add call trace log into changelog
>> - Remove 'dev_is_platform(dport->dport_dev)' checking out of cxl driver
>>   scope. Check if dport is emulated in cxl_test.
> I am suprised we got this far without this being a problem earlier.
>
> For the series you can add:
>
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
>
> ...can you also follow along with a rename, documentation, and cleanup
> patch?  cxl_setup_parent_dport() tells the reader absolutely nothing
> about what the function does, and that it is specifically initializing
> PCI AER operation.
>
> It should be called something like cxl_dport_init_aer(), and it should
> have kernel-doc associated with it. The cleanup opportunity I see is to
> consolidate the ->native_aer check for the cxl_rcrb_to_aer() and
> cxl_disable_rch_root_ints() into one location. It is a bit silly that
> cxl_disable_rch_root_ints() needs to check if dport->regs.dport_aer was
> initialized when it was just setup a few lines above. I.e. there are
> just too many helper functions and it all could be consolidated in a
> bigger cxl_dport_init_aer() function.

Sure, I will do that, thanks for review.


>
>> Li Ming (2):
>>   cxl/pci: Get AER capability address from RCRB only for RCH dport
>>   cxl/test: Skip cxl_setup_parent_dport() for emulated dports
> This is the right thing to do whenever possible. The usage of
> dev_is_platform() only makes sense for scenarios where a function is
> called by the cxl_core that needs to avoid getting confused by cxl_test.
>
> In this case, since cxl_mem is making the call to the exported
> cxl_setup_parent_dport() symbol, then mocking it for cxl_test is
> appropriate.