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

[Baolu Lu]

On 2023/7/11 9:40, Liu, Jingqi wrote:
> On 7/4/2023 3:54 PM, Tian, Kevin wrote:
> > > From: Liu, Jingqi <jingqi.liu@xxxxxxxxx>
> > > Sent: Monday, July 3, 2023 10:37 PM
> > >
> > > On 7/3/2023 3:15 PM, Tian, Kevin wrote:
> > > > > From: Liu, Jingqi <jingqi.liu@xxxxxxxxx>
> > > > > 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.

Best regards,
baolu