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

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Date:   Mon, 3 Jul 2023 22:37:03 +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 7/3/2023 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 ?
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.

BR,
Jingqi