Re: [PATCH v6 0/9] dax/hmem, cxl: Coordinate Soft Reserved handling with CXL and HMEM

[Koralahalli Channabasappa, Smita]

Hi Tomasz,

On 2/20/2026 1:45 AM, Tomasz Wolski wrote:
> Tested on QEMU and physical setups.
>
> I have one question about "Soft Reserve" parent entries in iomem.
> On QEMU I see parent "Soft Reserved":
>
> a90000000-b4fffffff : Soft Reserved
>    a90000000-b4fffffff : CXL Window 0
>      a90000000-b4fffffff : dax1.0
>        a90000000-b4fffffff : System RAM (kmem)
>
> While on my physical setup this is missing - not sure if this is okay?
>
> BIOS-e820: [mem 0x0000002070000000-0x000000a06fffffff] soft reserved
>
> 2070000000-606fffffff : CXL Window 0
>    2070000000-606fffffff : region0
>      2070000000-606fffffff : dax0.0
>        2070000000-606fffffff : System RAM (kmem)
> 6070000000-a06fffffff : CXL Window 1
>    6070000000-a06fffffff : region1
>      6070000000-a06fffffff : dax1.0
>        6070000000-a06fffffff : System RAM (kmem)

Thanks for testing on both setups!

On QEMU: there is no region, so HMEM took ownership of the Soft Reserved 
range (REGISTER path). Patch 9 then reintroduced the Soft Reserved entry 
back into the iomem tree to reflect HMEM ownership.

On physical setup: CXL fully claimed both ranges, region0 and region1 
assembled successfully (DROP path). Since CXL owns the memory, there's 
no Soft Reserved parent to reintroduce.

Soft Reserved appears in /proc/iomem only when CXL does not fully claim 
the range and HMEM takes over. Your physical setup is showing it 
correctly. Maybe CXL_REGION config is false or region assembly failed on 
and has cleaned up on QEMU so there aren't any regions?

Thanks,
Smita

> Tested-by: Tomasz Wolski <tomasz.wolski@xxxxxxxxxxx>