Re: Segment truncation in multi-segment PCI handling?

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.06.2024 21:52, Andrew Cooper wrote:
> On 07/06/2024 8:46 pm, Marek Marczykowski-Górecki wrote:
>> Hi,
>>
>> I've got a new system, and it has two PCI segments:
>>
>>     0000:00:00.0 Host bridge: Intel Corporation Device 7d14 (rev 04)
>>     0000:00:02.0 VGA compatible controller: Intel Corporation Meteor Lake-P 
>> [Intel Graphics] (rev 08)
>>     ...
>>     10000:e0:06.0 System peripheral: Intel Corporation RST VMD Managed 
>> Controller
>>     10000:e0:06.2 PCI bridge: Intel Corporation Device 7ecb (rev 10)
>>     10000:e1:00.0 Non-Volatile memory controller: Phison Electronics 
>> Corporation PS5021-E21 PCIe4 NVMe Controller (DRAM-less) (rev 01)
>>
>> But looks like Xen doesn't handle it correctly:
>>
>>     (XEN) 0000:e0:06.0: unknown type 0
>>     (XEN) 0000:e0:06.2: unknown type 0
>>     (XEN) 0000:e1:00.0: unknown type 0
>>     ...
>>     (XEN) ==== PCI devices ====
>>     (XEN) ==== segment 0000 ====
>>     (XEN) 0000:e1:00.0 - NULL - node -1 
>>     (XEN) 0000:e0:06.2 - NULL - node -1 
>>     (XEN) 0000:e0:06.0 - NULL - node -1 
>>     (XEN) 0000:2b:00.0 - d0 - node -1  - MSIs < 161 >
>>     (XEN) 0000:00:1f.6 - d0 - node -1  - MSIs < 148 >
>>     ...
>>
>> This isn't exactly surprising, since pci_sbdf_t.seg is uint16_t, so
>> 0x10000 doesn't fit. OSDev wiki says PCI Express can have 65536 PCI
>> Segment Groups, each with 256 bus segments.
>>
>> Fortunately, I don't need this to work, if I disable VMD in the
>> firmware, I get a single segment and everything works fine.
>>
> 
> This is a known issue.  Works is being done, albeit slowly.

Is work being done? After the design session in Prague I put it on my
todo list, but at low priority. I'd be happy to take it off there if I
knew someone else is looking into this.

> 0x10000 is indeed not a spec-compliant PCI segment.  It's something
> model specific the Linux VMD driver is doing.

I wouldn't call this "model specific" - this numbering is purely a
software one (and would need coordinating between Dom0 and Xen).

Jan