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

Koralahalli Channabasappa, Smita
2026-02-20T21:19:40Z

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@fujitsu.com>