linux-kernel - Re: [PATCH 02/13] iommu: Move bus setup to IOMMU device registration

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Message-ID: <60d6a35e-5d12-b8c2-b0d2-7155965a10e5@linux.intel.com>
Date:   Sat, 23 Apr 2022 17:00:45 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Robin Murphy <robin.murphy@....com>, joro@...tes.org,
        will@...nel.org
Cc:     jean-philippe@...aro.org, zhang.lyra@...il.com,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        thierry.reding@...il.com, linux-arm-kernel@...ts.infradead.org,
        gerald.schaefer@...ux.ibm.com
Subject: Re: [PATCH 02/13] iommu: Move bus setup to IOMMU device registration

On 2022/4/23 16:51, Lu Baolu wrote:
> On 2022/4/23 16:37, Robin Murphy wrote:
>> On 2022-04-23 09:01, Lu Baolu wrote:
>>> Hi Robin,
>>>
>>> On 2022/4/19 15:20, Robin Murphy wrote:
>>>> On 2022-04-19 00:37, Lu Baolu wrote:
>>>>> On 2022/4/19 6:09, Robin Murphy wrote:
>>>>>> On 2022-04-16 01:04, Lu Baolu wrote:
>>>>>>> On 2022/4/14 20:42, Robin Murphy wrote:
>>>>>>>> @@ -1883,27 +1900,12 @@ static int iommu_bus_init(struct 
>>>>>>>> bus_type *bus)
>>>>>>>>    */
>>>>>>>>   int bus_set_iommu(struct bus_type *bus, const struct iommu_ops 
>>>>>>>> *ops)
>>>>>>>>   {
>>>>>>>> -    int err;
>>>>>>>> -
>>>>>>>> -    if (ops == NULL) {
>>>>>>>> -        bus->iommu_ops = NULL;
>>>>>>>> -        return 0;
>>>>>>>> -    }
>>>>>>>> -
>>>>>>>> -    if (bus->iommu_ops != NULL)
>>>>>>>> +    if (bus->iommu_ops && ops && bus->iommu_ops != ops)
>>>>>>>>           return -EBUSY;
>>>>>>>>       bus->iommu_ops = ops;
>>>>>>>
>>>>>>> Do we still need to keep above lines in bus_set_iommu()?
>>>>>>
>>>>>> It preserves the existing behaviour until each callsite and its 
>>>>>> associated error handling are removed later on, which seems like 
>>>>>> as good a thing to do as any. Since I'm already relaxing 
>>>>>> iommu_device_register() to a warn-but-continue behaviour while it 
>>>>>> keeps the bus ops on life-support internally, I figured not 
>>>>>> changing too much at once would make it easier to bisect any 
>>>>>> potential issues arising from this first step.
>>>>>
>>>>> Fair enough. Thank you for the explanation.
>>>>>
>>>>> Do you have a public tree that I could pull these patches and try them
>>>>> on an Intel hardware? Or perhaps you have done this? I like the whole
>>>>> idea of this series, but it's better to try it with a real hardware.
>>>>
>>>> I haven't bothered with separate branches since there's so many 
>>>> different pieces in-flight, but my complete (unstable) development 
>>>> branch can be found here:
>>>>
>>>> https://gitlab.arm.com/linux-arm/linux-rm/-/commits/iommu/bus
>>>>
>>>> For now I'd recommend winding the head back to "iommu: Clean up 
>>>> bus_set_iommu()" for testing - some of the patches above that have 
>>>> already been posted and picked up by their respective subsystems, 
>>>> but others are incomplete and barely compile-tested. I'll probably 
>>>> rearrange it later this week to better reflect what's happened so far.
>>>
>>> I wound the head back to "iommu: Clean up bus_set_iommu" and tested it
>>> on an Intel machine. It got stuck during boot. This test was on a remote
>>> machine and I have no means to access it physically. So I can't get any
>>> kernel debugging messages. (I have to work from home these days. :-()
>>>
>>> I guess it's due to the fact that intel_iommu_probe_device() callback
>>> only works for the pci devices. The issue occurs when probing a device
>>> other than a PCI one.
>>
>> Yeah, I was wondering if that would be significant, since it's the 
>> only driver that never registered itself for platform_bus_type so 
>> won't have actually seen those calls before. I'm inclined to bodge 
>> that as below for now, as long as it then works OK in terms of the 
>> rest of the changes.
>>
>> Thanks,
>> Robin.
>>
>> ----->8-----
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>> index 9fa1b98186a3..6e359f92ec00 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -4565,6 +4565,10 @@ static struct iommu_device 
>> *intel_iommu_probe_device(struct device *dev)
>>       unsigned long flags;
>>       u8 bus, devfn;
>>
>> +    /* ANDD platform device support needs fixing */
>> +    if (!pdev)
>> +        return ERR_PTR(-ENODEV);
>> +
>>       iommu = device_to_iommu(dev, &bus, &devfn);
>>       if (!iommu)
>>           return ERR_PTR(-ENODEV);
> 
> I haven't seen any real ANDD platform devices, hence this works for me.

Or more precisely, return NULL when @dev goes through device_to_iommu()?

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index df5c62ecf942..0d447739e076 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -797,8 +797,11 @@ struct intel_iommu *device_to_iommu(struct device 
*dev, u8 *bus, u8 *devfn)
                 pf_pdev = pci_physfn(pdev);
                 dev = &pf_pdev->dev;
                 segment = pci_domain_nr(pdev->bus);
-       } else if (has_acpi_companion(dev))
+       } else if (has_acpi_companion(dev)) {
                 dev = &ACPI_COMPANION(dev)->dev;
+       } else {
+               return NULL;
+       }

         rcu_read_lock();
         for_each_iommu(iommu, drhd) {

Best regards,
baolu