Re: [PATCH 0/2] iommu: Add io_ptdump debug interface for iommu

[Qinxin Xia <xiaqinxin@huawei.com>]

On 2025/9/16 00:28:10, Jason Gunthorpe <jgg@ziepe.ca> wrote:
> On Thu, Sep 11, 2025 at 10:08:55PM +0800, Qinxin Xia wrote:
>>
>>
>> On 2025/9/10 22:15:47, Jason Gunthorpe <jgg@ziepe.ca> wrote:
>>> On Wed, Sep 10, 2025 at 11:20:08AM +0800, Qinxin Xia wrote:
>>>> Ok, I see, my colleague Wang Zhou also released a version of io_ptdump
>>>> a long time ago, which is implemented in smmu debugfs. Will recommends that
>>>> io_ptdump be implemented in a way similar to CPU page table dump. Using
>>>> debugfs to expose the data and using format-specific callbacks to implement
>>>> specific data dumps, I'll talk to him about this as well.
>>>
>>> I feel we should have a iommu subsystem debugfs and per-iommu_domain
>>> directories to dump the page tables.
>>>
>>> The smmu debugfs can report what iommu_domains each STE/CD is
>>> referencing.
>>>
>>> This also needs RCU freeing of page table levels as a locking
>>> strategy.
>>
>> Thanks, I'll add RCU in the next version, but there's some
>> confusion,
> 
> Please don't, RCU is quite complicated, I don't really want to see
> attempts to retrofit it into the existing page table code. This is why
> I've said debugging like this needs to go along with the new iommu pt
> work to consolidate the page table code.
> 
>> Do you
>> mean to create a directory for each domain? like：
>>
>> /sys/kernel/debug/io_page_tables/domain_xxxx (xxxx=domain addr)
> 
> Something like this could be a reasonable option.
> 
>> tree domain_xxxx like:
>> domain_xxxx
>> └── group x
>> │ └── device
> 
> Though I would probably not include this information..
> 
Users could be difficult to map domain to devices, so I think maybe
we should provide the device information contained in the domain.>> └── 
DebugFS file: /sys/kernel/debug/io_page_tables
>> └── Operation: Reading this file triggers the entire debug information
>> collection process
> 
> I don't think we want to dump every page table in the system in one
> file.
> 
>> Do you mean that the interface in io-pgtable-arm.c is directly invoked
>> during the process of obtaining page table information without passing
>> through arm-smmu-v3.c?
> 
> Yes, this is what iommu pt brings.
> 
> Jason