From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 13E1E25B2F4; Thu, 12 Feb 2026 20:59:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770929994; cv=none; b=lUvqVDbLuWTxgrAHja99+bC/5SfdIjIgyUKvCfdhR8HANBqOym3Cd2zZdqF6svFXCo1vskmUHNwdfzAj3FeBdM1aFGVYLesCIadnvdyCKel68S87EfEQvJ6RzCmPJj69YEljutawkUlRhZGA/MzcPfmo8HLl/nuoIzdFnXFZx/w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770929994; c=relaxed/simple; bh=wgJKQfmxOzsKstGBY6rLl+Aq49bQ/slkNHMgqOHPRxQ=; h=Date:To:From:Subject:Message-Id; b=Hexa/sIMGDEH+Db0/NkXXgT4hnpD2cDeY4ptvkUVHm8t3MI2fxJDnp+97wA3W5Y7Up/yvgjlef9lJHsVp77L57I684nAArwAxtz0syNcipfgZ9E02Sq9j3tLl+nU1EryJ0PphGPaCBE2pfFul85x1+umRSPXQXREZPyH0hki7n0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=Z6mm+czl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="Z6mm+czl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 87A9AC4CEF7; Thu, 12 Feb 2026 20:59:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1770929993; bh=wgJKQfmxOzsKstGBY6rLl+Aq49bQ/slkNHMgqOHPRxQ=; h=Date:To:From:Subject:From; b=Z6mm+czlaIiffWRu2xFuftV/5TC7BBkWNd8ty7wpJwYAJT1gfAVKWe3qgYvNylUBG yE7c0cG25/K/Xwy9ZhhZZFpIaWe1alrSk//PjNCRd5dDMdYVKhC9UObLIlF8daYXXE NXNrSe0t7EGQok7vqmpoO5nhKbGJ6R9ETdOxJG8Q= Date: Thu, 12 Feb 2026 12:59:52 -0800 To: mm-commits@vger.kernel.org,wangyinfeng@phytium.com.cn,stable@vger.kernel.org,rppt@kernel.org,jonathan.cameron@huawei.com,gourry@gourry.net,david@kernel.org,dan.j.williams@intel.com,cuichao1753@phytium.com.cn,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-numa_memblks-identify-the-accurate-numa-id-of-cfmw.patch added to mm-new branch Message-Id: <20260212205953.87A9AC4CEF7@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm: numa_memblks: identify the accurate NUMA ID of CFMW has been added to the -mm mm-new branch. Its filename is mm-numa_memblks-identify-the-accurate-numa-id-of-cfmw.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-numa_memblks-identify-the-accurate-numa-id-of-cfmw.patch This patch will later appear in the mm-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Note, mm-new is a provisional staging ground for work-in-progress patches, and acceptance into mm-new is a notification for others take notice and to finish up reviews. Please do not hesitate to respond to review feedback and post updated versions to replace or incrementally fixup patches in mm-new. The mm-new branch of mm.git is not included in linux-next Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Cui Chao Subject: mm: numa_memblks: identify the accurate NUMA ID of CFMW Date: Wed, 11 Feb 2026 18:33:20 +0800 In some physical memory layout designs, the address space of CFMW (CXL Fixed Memory Window) resides between multiple segments of system memory belonging to the same NUMA node. In numa_cleanup_meminfo, these multiple segments of system memory are merged into a larger numa_memblk. When identifying which NUMA node the CFMW belongs to, it may be incorrectly assigned to the NUMA node of the merged system memory. When a CXL RAM region is created in userspace, the memory capacity of the newly created region is not added to the CFMW-dedicated NUMA node. Instead, it is accumulated into an existing NUMA node (e.g., NUMA0 containing RAM). This makes it impossible to clearly distinguish between the two types of memory, which may affect memory-tiering applications. Example memory layout: Physical address space: 0x00000000 - 0x1FFFFFFF System RAM (node0) 0x20000000 - 0x2FFFFFFF CXL CFMW (node2) 0x40000000 - 0x5FFFFFFF System RAM (node0) 0x60000000 - 0x7FFFFFFF System RAM (node1) After numa_cleanup_meminfo, the two node0 segments are merged into one: 0x00000000 - 0x5FFFFFFF System RAM (node0) // CFMW is inside the range 0x60000000 - 0x7FFFFFFF System RAM (node1) So the CFMW (0x20000000-0x2FFFFFFF) will be incorrectly assigned to node0. To address this scenario, accurately identifying the correct NUMA node can be achieved by checking whether the region belongs to both numa_meminfo and numa_reserved_meminfo. While this issue is only observed in a QEMU configuration, and no known end users are impacted by this problem, it is likely that some firmware implementation is leaving memory map holes in a CXL Fixed Memory Window. CXL hotplug depends on mapping free window capacity, and it seems to be only a coincidence to have not hit this problem yet. 1. Issue Impact and Backport Recommendation: This patch fixes an issue observed in QEMU emulation where, during the dynamic creation of a CXL RAM region, the memory capacity is not assigned to the correct CFMW-dedicated NUMA node. While hardware platforms could potentially have such memory configurations, we are not currently aware of any such hardware. This issue leads to: Failure of the memory tiering mechanism: The system is designed to treat System RAM as fast memory and CXL memory as slow memory. For performance optimization, hot pages may be migrated to fast memory while cold pages are migrated to slow memory. The system uses NUMA IDs as an index to identify different tiers of memory. If the NUMA ID for CXL memory is calculated incorrectly and its capacity is aggregated into the NUMA node containing System RAM (i.e., the node for fast memory), the CXL memory cannot be correctly identified. It may be misjudged as fast memory, thereby affecting performance optimization strategies. Inability to distinguish between System RAM and CXL memory even for simple manual binding: Tools like |numactl|and other NUMA policy utilities cannot differentiate between System RAM and CXL memory, making it impossible to perform reasonable memory binding. Inaccurate system reporting: Tools like |numactl -H|would display memory capacities that do not match the actual physical hardware layout, impacting operations and monitoring. This issue affects all users utilizing the CXL RAM functionality who rely on memory tiering or NUMA-aware scheduling. Therefore, I recommend backporting this patch to all stable kernel series that support dynamic CXL region creation. 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. Considering factors like hardware platform architecture, memory resources, and others, such a physical address layout can indeed occur. This patch does not introduce risk; it simply correctly handles the NUMA node assignment for CXL RAM regions within such a physical address layout. Thus, I believe a kernel fix is necessary. Link: https://lkml.kernel.org/r/20260211103320.2064211-2-cuichao1753@phytium.com.cn Fixes: 779dd20cfb56 ("cxl/region: Add region creation support") Signed-off-by: Cui Chao Reviewed-by: Jonathan Cameron Reviewed-by: Gregory Price Reviewed-by: Dan Williams Cc: David Hildenbrand Cc: Mike Rapoport Cc: Wang Yinfeng Cc: Signed-off-by: Andrew Morton --- mm/numa_memblks.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) --- a/mm/numa_memblks.c~mm-numa_memblks-identify-the-accurate-numa-id-of-cfmw +++ a/mm/numa_memblks.c @@ -570,15 +570,16 @@ static int meminfo_to_nid(struct numa_me int phys_to_target_node(u64 start) { int nid = meminfo_to_nid(&numa_meminfo, start); + int reserved_nid = meminfo_to_nid(&numa_reserved_meminfo, start); /* - * Prefer online nodes, but if reserved memory might be - * hot-added continue the search with reserved ranges. + * Prefer online nodes unless the address is also described + * by reserved ranges, in which case use the reserved nid. */ - if (nid != NUMA_NO_NODE) + if (nid != NUMA_NO_NODE && reserved_nid == NUMA_NO_NODE) return nid; - return meminfo_to_nid(&numa_reserved_meminfo, start); + return reserved_nid; } EXPORT_SYMBOL_GPL(phys_to_target_node); _ Patches currently in -mm which might be from cuichao1753@phytium.com.cn are mm-numa_memblks-identify-the-accurate-numa-id-of-cfmw.patch