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...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: "Mike Rapoport (IBM)" rppt@kernel.org 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@kernel.org Signed-off-by: Mike Rapoport (IBM) rppt@kernel.org Reported-by: Qi Zheng zhengqi.arch@bytedance.com Closes: https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.co... Acked-by: David Hildenbrand david@redhat.com Acked-by: Michal Hocko mhocko@suse.com Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov (AMD) bp@alien8.de Cc: Dave Hansen dave.hansen@linux.intel.com Cc: H. Peter Anvin hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: Peter Ziljstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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@kernel.org 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