The patch titled Subject: x86/mm: drop 4MB restriction on minimal NUMA node size has been added to the -mm mm-hotfixes-unstable branch. Its filename is x86-mm-drop-4mb-restriction-on-minimal-numa-node-size.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/x86-mm-drop-4mb-restriction-on-minimal-numa-node-size.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm 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 the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: "Mike Rapoport (IBM)" <rppt@xxxxxxxxxx> Subject: x86/mm: drop 4MB restriction on minimal NUMA node size Date: Tue, 17 Oct 2023 09:22:15 +0300 Qi Zheng reports crashes in a production environment and provides a simplified example as a reproducer: For example, if we use qemu to start a two NUMA node kernel, one of the nodes has 2M memory (less than NODE_MIN_SIZE), and the other node has 2G, then we will encounter the following panic: [ 0.149844] BUG: kernel NULL pointer dereference, address: 0000000000000000 [ 0.150783] #PF: supervisor write access in kernel mode [ 0.151488] #PF: error_code(0x0002) - not-present page <...> [ 0.156056] RIP: 0010:_raw_spin_lock_irqsave+0x22/0x40 <...> [ 0.169781] Call Trace: [ 0.170159] <TASK> [ 0.170448] deactivate_slab+0x187/0x3c0 [ 0.171031] ? bootstrap+0x1b/0x10e [ 0.171559] ? preempt_count_sub+0x9/0xa0 [ 0.172145] ? kmem_cache_alloc+0x12c/0x440 [ 0.172735] ? bootstrap+0x1b/0x10e [ 0.173236] bootstrap+0x6b/0x10e [ 0.173720] kmem_cache_init+0x10a/0x188 [ 0.174240] start_kernel+0x415/0x6ac [ 0.174738] secondary_startup_64_no_verify+0xe0/0xeb [ 0.175417] </TASK> [ 0.175713] Modules linked in: [ 0.176117] CR2: 0000000000000000 The crashes happen because of inconsistency between nodemask that has nodes with less than 4MB as memoryless and the actual memory fed into core mm. The commit 9391a3f9c7f1 ("[PATCH] x86_64: Clear more state when ignoring empty node in SRAT parsing") that introduced minimal size of a NUMA node does not explain why a node size cannot be less than 4MB and what boot failures this restriction might fix. Since then a lot has changed and core mm won't confuse badly about small node sizes. Drop the limitation for the minimal node size. Link: https://lkml.kernel.org/r/20231017062215.171670-1-rppt@xxxxxxxxxx Signed-off-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx> Reported-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> Closes: https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@xxxxxxxxxxxxx/ Acked-by: David Hildenbrand <david@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Borislav Petkov (AMD) <bp@xxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Peter Ziljstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/x86/include/asm/numa.h | 7 ------- arch/x86/mm/numa.c | 7 ------- 2 files changed, 14 deletions(-) --- a/arch/x86/include/asm/numa.h~x86-mm-drop-4mb-restriction-on-minimal-numa-node-size +++ a/arch/x86/include/asm/numa.h @@ -12,13 +12,6 @@ #define NR_NODE_MEMBLKS (MAX_NUMNODES*2) -/* - * Too small node sizes may confuse the VM badly. Usually they - * result from BIOS bugs. So dont recognize nodes as standalone - * NUMA entities that have less than this amount of RAM listed: - */ -#define NODE_MIN_SIZE (4*1024*1024) - extern int numa_off; /* --- a/arch/x86/mm/numa.c~x86-mm-drop-4mb-restriction-on-minimal-numa-node-size +++ a/arch/x86/mm/numa.c @@ -601,13 +601,6 @@ static int __init numa_register_memblks( if (start >= end) continue; - /* - * Don't confuse VM with a node that doesn't have the - * minimum amount of memory: - */ - if (end && (end - start) < NODE_MIN_SIZE) - continue; - alloc_node_data(nid); } _ Patches currently in -mm which might be from rppt@xxxxxxxxxx are x86-mm-drop-4mb-restriction-on-minimal-numa-node-size.patch nios2-define-virtual-address-space-for-modules.patch mm-introduce-execmem_text_alloc-and-execmem_free.patch mm-execmem-arch-convert-simple-overrides-of-module_alloc-to-execmem.patch mm-execmem-arch-convert-remaining-overrides-of-module_alloc-to-execmem.patch modules-execmem-drop-module_alloc.patch mm-execmem-introduce-execmem_data_alloc.patch arm64-execmem-extend-execmem_params-for-generated-code-allocations.patch riscv-extend-execmem_params-for-generated-code-allocations.patch powerpc-extend-execmem_params-for-kprobes-allocations.patch powerpc-extend-execmem_params-for-kprobes-allocations-fix.patch arch-make-execmem-setup-available-regardless-of-config_modules.patch x86-ftrace-enable-dynamic-ftrace-without-config_modules.patch kprobes-remove-dependency-on-config_modules.patch bpf-remove-config_bpf_jit-dependency-on-config_modules-of.patch