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

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Date:   Tue, 11 Jul 2023 09:40:37 +0800
From:   "Liu, Jingqi" <jingqi.liu@...el.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        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 7/4/2023 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.

Thanks,
Jingqi