linux-kernel - Re: [PATCH 0/5] iommu/vt-d: debugfs: Enhancements to IOMMU debugfs

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Message-ID: <0c17e548-cca2-2f6b-b9c5-a534f5886e03@intel.com>
Date:   Tue, 11 Jul 2023 14:23:05 +0800
From:   "Liu, Jingqi" <jingqi.liu@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/5] iommu/vt-d: debugfs: Enhancements to IOMMU debugfs

On 7/11/2023 10:52 AM, Baolu Lu wrote:
> On 2023/7/11 9:40, Liu, Jingqi wrote:
>> On 7/4/2023 3:54 PM, Tian, Kevin wrote:
>>>> From: Liu, Jingqi <jingqi.liu@...el.com>
>>>> Sent: Monday, July 3, 2023 10:37 PM
>>>>
>>>> On 7/3/2023 3:15 PM, Tian, Kevin wrote:
>>>>>> From: Liu, Jingqi <jingqi.liu@...el.com>
>>>>>> Sent: Sunday, June 25, 2023 11:05 PM
>>>>>>
>>>>>> The original debugfs only dumps all IOMMU page tables without pasid
>>>>>> supported. It traverses all devices on the pci bus, then dumps 
>>>>>> all page
>>>>>> tables based on device domains. This traversal is from software
>>>>>> perspective.
>>>>>>
>>>>>> This series dumps page tables by traversing root tables, context 
>>>>>> tables,
>>>>>> pasid directories and pasid tables from hardware perspective. By
>>>>>> specifying source identifier and PASID, it supports dumping 
>>>>>> specified
>>>>>> page table or all page tables in legacy mode or scalable mode.
>>>>>>
>>>>>> For a device that only supports legacy mode, specify the source
>>>>>> identifier, and search the root table and context table to dump its
>>>>>> page table. It does not support to specify PASID.
>>>>>>
>>>>>> For a device that supports scalable mode, specify a
>>>>>> {source identifier, PASID} pair and search the root table, 
>>>>>> context table
>>>>>> and pasid table to dump its page table.  If the pasid is not 
>>>>>> specified,
>>>>>> it is set to RID_PASID.
>>>>>>
>>>>>> Switch to dump all page tables by specifying "auto".
>>>>>>
>>>>>> Examples are as follows:
>>>>>> 1) Dump the page table of device "00:1f.0" that only supports legacy
>>>>>> mode.
>>>>>>
>>>>>> $ sudo echo 00:1f.0 >
>>>>>> /sys/kernel/debug/iommu/intel/domain_translation_struct
>>>>>> $ sudo cat /sys/kernel/debug/iommu/intel/domain_translation_struct
>>>>>> Device 0000:00:1f.0 @0x105407000
>>>>>> IOVA_PFN                PML5E                   PML4E
>>>>>> 0x0000000000000 |       0x0000000000000000 0x0000000105408003
>>>>>> 0x0000000000001 |       0x0000000000000000 0x0000000105408003
>>>>>> 0x0000000000002 |       0x0000000000000000 0x0000000105408003
>>>>>> 0x0000000000003 |       0x0000000000000000 0x0000000105408003
>>>>>>
>>>>>> PDPE                    PDE                     PTE
>>>>>> 0x0000000105409003      0x000000010540a003 0x0000000000000003
>>>>>> 0x0000000105409003      0x000000010540a003 0x0000000000001003
>>>>>> 0x0000000105409003      0x000000010540a003 0x0000000000002003
>>>>>> 0x0000000105409003      0x000000010540a003 0x0000000000003003
>>>>>>
>>>>>> [...]
>>>>>>
>>>>>> 2) Dump the page table of device "00:0a.0" with pasid "2".
>>>>>>
>>>>>> $ sudo echo 00:0a.0,2 >
>>>>>> /sys/kernel/debug/iommu/intel/domain_translation_struct
>>>>>> $ sudo cat /sys/kernel/debug/iommu/intel/domain_translation_struct
>>>>> What about creating a directory layout per {dev, pasid} so the 
>>>>> user can
>>>>> easily figure out and dump?
>>>>>
>>>>> e.g.
>>>>>
>>>>> /sys/kernel/debug/iommu/intel/00:0a.0/0/domain_translation_struct
>>>>> /sys/kernel/debug/iommu/intel/00:0a.0/2/domain_translation_struct
>>>> Thanks.
>>>>
>>>> Do you mean create a directory for each device, whether it supports
>>>> PASID or not ?
>>> every device has PASID#0 valid, i.e. RID2PASID.
>> Sorry for the late response.
>> Got it. Thanks.
>>>> Seems the PASID can be assigned at runtime.
>>>> So it needs to support creating debugfs file at runtime in IOMMU 
>>>> driver.
>>>> Looks like this requires modifying IOMMU driver.
>>>>
>>> Isn't this patch trying to modify the driver?
>> I just tried not to modify the driver except debugfs.
>> I'll try this implementation. [
>
> I'd second Kevin's suggestion.
>
> If you check how usb xhci dumps its contexts for devices, you can see
> the similar scheme.
>
> # ls /sys/kernel/debug/usb/xhci/0000:00:14.0/devices
> 01  02  03  04  05
>
> In our case, pasid 0 is special which denotes the domain attached to the
> RID.
Thanks for your info.
This implementation is more friendly for user.
I'll implement it as such.

BR,
Jingqi