On 2025/5/21 14:25, Jan Beulich wrote:
> On 21.05.2025 08:08, Chen, Jiqian wrote:
>> On 2025/5/19 21:21, Roger Pau Monné wrote:
>>> On Mon, May 19, 2025 at 03:10:17PM +0200, Jan Beulich wrote:
>>>> On 19.05.2025 09:13, Chen, Jiqian wrote:
>>>>> On 2025/5/19 14:56, Jan Beulich wrote:
>>>>>> On 19.05.2025 08:43, Chen, Jiqian wrote:
>>>>>>> On 2025/5/18 22:20, Jan Beulich wrote:
>>>>>>>> On 09.05.2025 11:05, Jiqian Chen wrote:
>>>>>>>>> @@ -827,6 +827,34 @@ static int vpci_init_capability_list(struct
>>>>>>>>> pci_dev *pdev)
>>>>>>>>>
>>>>>>>>> PCI_STATUS_RSVDZ_MASK);
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>> +static int vpci_init_ext_capability_list(struct pci_dev *pdev)
>>>>>>>>> +{
>>>>>>>>> + unsigned int pos = PCI_CFG_SPACE_SIZE, ttl = 480;
>>>>>>>>
>>>>>>>> The ttl value exists (in the function you took it from) to make sure
>>>>>>>> the loop below eventually ends. That is, to be able to kind of
>>>>>>>> gracefully deal with loops in the linked list. Such loops, however,
>>>>>>>> would ...
>>>>>>>>
>>>>>>>>> + if ( !is_hardware_domain(pdev->domain) )
>>>>>>>>> + /* Extended capabilities read as zero, write ignore for
>>>>>>>>> guest */
>>>>>>>>> + return vpci_add_register(pdev->vpci, vpci_read_val, NULL,
>>>>>>>>> + pos, 4, (void *)0);
>>>>>>>>> +
>>>>>>>>> + while ( pos >= PCI_CFG_SPACE_SIZE && ttl-- )
>>>>>>>>> + {
>>>>>>>>> + uint32_t header = pci_conf_read32(pdev->sbdf, pos);
>>>>>>>>> + int rc;
>>>>>>>>> +
>>>>>>>>> + if ( !header )
>>>>>>>>> + return 0;
>>>>>>>>> +
>>>>>>>>> + rc = vpci_add_register(pdev->vpci, vpci_read_val,
>>>>>>>>> vpci_hw_write32,
>>>>>>>>> + pos, 4, (void *)(uintptr_t)header);
>>>>>>>>
>>>>>>>> ... mean we may invoke this twice for the same capability. Such
>>>>>>>> a secondary invocation would fail with -EEXIST, causing device init
>>>>>>>> to fail altogether. Which is kind of against our aim of exposing
>>>>>>>> (in a controlled manner) as much of the PCI hardware as possible.
>>>>>>> May I know what situation that can make this twice for one capability
>>>>>>> when initialization?
>>>>>>> Does hardware capability list have a cycle?
>>>>>>
>>>>>> Any of this is to work around flawed hardware, I suppose.
>>>>>>
>>>>>>>> Imo we ought to be using a bitmap to detect the situation earlier
>>>>>>>> and hence to be able to avoid redundant register addition. Thoughts?
>>>>>>> Can we just let it go forward and continue to add register for next
>>>>>>> capability when rc == -EXIST, instead of returning error ?
>>>>>>
>>>>>> Possible, but feels wrong.
>>>>> How about when EXIST, setting the next bits of previous extended
>>>>> capability to be zero and return 0? Then we break the cycle.
>>>>
>>>> Hmm. Again an option, yet again I'm not certain. But that's perhaps just
>>>> me, and Roger may be fine with it. IOW we might as well start out this way,
>>>> and adjust if (ever) an issue with a real device is found.
>>>
>>> Returning -EEXIST might be fine, but at that point there's no further
>>> capability to process. There's a loop in the linked capability list,
>>> and we should just exit. There needs to be a warning in this case,
>>> and since this is for the hardware domain only it shouldn't be fatal.
>>>
>> If I understand correctly, I need to add below in next version?
>>
>> rc = vpci_add_register(pdev->vpci, vpci_read_val, vpci_hw_write32,
>> pos, 4, (void *)(uintptr_t)header);
>> +
>> + if ( rc == -EEXIST )
>> + {
>> + printk(XENLOG_WARNING
>> + "%pd %pp: there is a loop in the linked capability
>> list\n",
>
> I think we shouldn't say "loop" unless we firmly know that's what the
> issue is. Maybe use "overlap" instead? And then also log the offending
> register range? (As a nit: "there is" and "linked" are not adding any
> value to the log message; to keep them short [without losing
> information], please try to avoid such.)
OK, below may be more in line with your opinion.
rc = vpci_add_register(pdev->vpci, vpci_read_val, vpci_hw_write32,
pos, 4, (void *)(uintptr_t)header);
+
+ if ( rc == -EEXIST )
+ {
+ printk(XENLOG_WARNING
+ "%pd %pp: overlap in extended cap list, offset %#x\n",
+ pdev->domain, &pdev->sbdf, pos);
+ return 0;
+ }
+
if ( rc )
return rc;
>
> Jan
--
Best regards,
Jiqian Chen.
