linux-kernel - Re: [PATCH v4 0/9] dax/hmem, cxl: Coordinate Soft Reserved handling with CXL and HMEM

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Message-ID: <20251205230445.16100-1-tomasz.wolski@fujitsu.com>
Date: Sat,  6 Dec 2025 00:04:35 +0100
From: Tomasz Wolski <tomasz.wolski@...itsu.com>
To: y-goto@...itsu.com
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Subject: Re: [PATCH v4 0/9] dax/hmem, cxl: Coordinate Soft Reserved handling with CXL and HMEM

Hello Dan & Gotou-san,

Many thanks for your remarks for the test cases
For the qemu tests I used modified qemu and sebios, therefore some 'strange' cases
are only testable on virtual setups - thanks for making it clear which configurations
are supported in real life

>> 
>> [4] Physical machine: 2 CFMWS + Host-bridge + 2 CXL devices
>> 
>> kernel: 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)
>
>Ok, so a real world maching that creates a merged 0x0000002070000000-0x000000a06fffffff range. Can you confirm that the SRAT has separate entries for those ranges? >Otherwise, need to rethink how to keep this fallback algorithm simple and predictable.

I looked into the syslogs and I see the SRAT has separate entries:

[    0.005128] [      T0] ACPI: SRAT: Node 2 PXM 2 [mem 0x2070000000-0x606fffffff] hotplug
[    0.005129] [      T0] ACPI: SRAT: Node 2 PXM 2 [mem 0x6070000000-0xa06fffffff] hotplug