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

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Date:   Tue, 4 Jul 2023 07:54:58 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     "Liu, Jingqi" <jingqi.liu@...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

> 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.

> 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?