linux-kernel - Re: [PATCH v2 1/1] mm: numa_memblks: Identify the accurate NUMA ID of CFMW

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Message-ID: <a90bc6f2-105c-4ffc-99d9-4fa5eaa79c45@phytium.com.cn>
Date: Mon, 26 Jan 2026 17:06:52 +0800
From: Cui Chao <cuichao1753@...tium.com.cn>
To: Gregory Price <gourry@...rry.net>
Cc: dan.j.williams@...el.com, Andrew Morton <akpm@...ux-foundation.org>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Mike Rapoport <rppt@...nel.org>, Wang Yinfeng <wangyinfeng@...tium.com.cn>,
 linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 1/1] mm: numa_memblks: Identify the accurate NUMA ID of
 CFMW


On 1/24/2026 12:46 AM, Gregory Price wrote:
> On Thu, Jan 22, 2026 at 04:03:49PM +0800, Cui Chao wrote:
>> 2.Why a Kernel Update is Recommended Over a Firmware Update:
>>
>> In the scenario of dynamic CXL region creation, the association between the
>> memory's HPA range and its corresponding NUMA node is established when the
>> kernel driver performs the commit operation. This is a runtime, OS-managed
>> operation where the platform firmware cannot intervene to provide a fix.
>>
> This is not accurate
>
> The memory-to-node association for CXL memory is built by acpi logic:
>
>     linux/drivers/acpi/numa/srat.c
>
> Specifically:
>
>     acpi_parse_memory_affinity()  /* if SRAT entry exists */
>        -> numa_add_memblk(node, start, end)
>
>     acpi_parse_cfmws()  /* if no SRAT entry exists */
>        -> numa_add_reserved_memblk(node, start, end)
>
>
> This patch implies the latter is occurring - as it queries the reserved
> block associations - meaning your platform is not shipping SRAT tables
> for CXL memory regions.
Sorry，my previous statement was ambiguous. What I intended to convey is 
that the moment when CXL memory is actually assigned to a dedicated NUMA 
node and becomes ready for use by applications is precisely during the 
creation of the region.
> We have only seen this in QEMU - and this is correctable in firmware.
>
> But if this is shipped hardware, letting us know the platform lets us
> know whether we should backport it.
>
> ---
>
> All that said, this does look harmless, and seems reasonable - but the
> changelog should reflect what the hardware is doing above.
This issue was discovered on the QEMU platform. I need to apologize for 
my earlier imprecise statement (claiming it was hardware instead of 
QEMU). My core point at the time was to emphasize that this is a problem 
in the general code path when facing this scenario, not a QEMU-specific 
emulation issue, and therefore it could theoretically affect real 
hardware as well. I apologize for any confusion this may have caused.
>
> ~Gregory

-- 
Best regards,
Cui Chao.