Re: [PATCH v8 01/17] memblock: add MEMBLOCK_RSRV_KERN flag

Pratyush Yadav
2025-10-13T14:59:38Z

On Fri, Oct 10 2025, Breno Leitao wrote:

> Hello Chanyuan, Mike,
>
> On Fri, May 09, 2025 at 12:46:19AM -0700, Changyuan Lyu wrote:
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -492,7 +492,7 @@ static int __init_memblock memblock_double_array(struct memblock_type *type,
>> * needn't do it
>> */
>> if (!use_slab)
>> - BUG_ON(memblock_reserve(addr, new_alloc_size));
>> + BUG_ON(memblock_reserve_kern(addr, new_alloc_size));
>>
>> /* Update slab flag */
>> *in_slab = use_slab;
>> @@ -642,7 +642,7 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
>> #ifdef CONFIG_NUMA
>> WARN_ON(nid != memblock_get_region_node(rgn));
>> #endif
>> - WARN_ON(flags != rgn->flags);
>> + WARN_ON(flags != MEMBLOCK_NONE && flags != rgn->flags);
>
> I am hitting some sporadic warnings at early boot on a production kernel
> (6.16). Unfortunately this issue is not easily reproduce for me to test on
> upstream.
>
> 09:14:44 BIOS-provided physical RAM map:
> 09:14:44 BIOS-e820: [mem 0x0000000000000000-0x000000000009ffff] usable
> 09:14:44 BIOS-e820: [mem 0x00000000000a0000-0x00000000000fffff] reserved
> 09:14:44 BIOS-e820: [mem 0x0000000000100000-0x0000000064cb7fff] usable
> 09:14:44 BIOS-e820: [mem 0x0000000064cb8000-0x0000000064dc3fff] reserved
> 09:14:44 BIOS-e820: [mem 0x0000000064dc4000-0x0000000065b13fff] usable
> 09:14:44 BIOS-e820: [mem 0x0000000065b14000-0x0000000065b61fff] reserved
> 09:14:44 BIOS-e820: [mem 0x0000000065b62000-0x0000000065ed0fff] usable
> 09:14:44 BIOS-e820: [mem 0x0000000065ed1000-0x0000000065f2bfff] reserved
> 09:14:44 BIOS-e820: [mem 0x0000000065f2c000-0x0000000066621fff] usable
> 09:14:44 BIOS-e820: [mem 0x0000000066622000-0x0000000066630fff] reserved
> 09:14:44 BIOS-e820: [mem 0x0000000066631000-0x0000000068107fff] usable
> 09:14:44 BIOS-e820: [mem 0x0000000068108000-0x000000006819dfff] ACPI data
> 09:14:44 BIOS-e820: [mem 0x000000006819e000-0x000000006a48cfff] usable
> 09:14:44 BIOS-e820: [mem 0x000000006a48d000-0x000000006c58cfff] reserved
> 09:14:44 BIOS-e820: [mem 0x000000006c58d000-0x000000006c5dcfff] ACPI data
> 09:14:44 BIOS-e820: [mem 0x000000006c5dd000-0x000000006cfdcfff] ACPI NVS
> 09:14:44 BIOS-e820: [mem 0x000000006cfdd000-0x000000006e9fcfff] reserved
> 09:14:44 BIOS-e820: [mem 0x000000006e9fd000-0x000000006fffffff] usable
> 09:14:44 BIOS-e820: [mem 0x0000000070000000-0x000000008fffffff] reserved
> 09:14:44 BIOS-e820: [mem 0x00000000fd000000-0x00000000fe7fffff] reserved
> 09:14:44 BIOS-e820: [mem 0x00000000fed20000-0x00000000fed44fff] reserved
> 09:14:44 BIOS-e820: [mem 0x00000000ff000000-0x00000000ffffffff] reserved
> 09:14:44 BIOS-e820: [mem 0x0000000100000000-0x000000107fff655f] usable
> 09:14:44 BIOS-e820: [mem 0x000000107fff6560-0x000000107fff656f] type 128
> 09:14:44 BIOS-e820: [mem 0x000000107fff6570-0x000000107fffffff] usable
> 09:14:44 random: crng init done
> 09:14:44 ------------[ cut here ]------------
> 09:14:44 WARNING: CPU: 0 PID: 0 at mm/memblock.c:668 memblock_add_range (mm/memblock.c:668)
> 09:14:44 Modules linked in:
> 09:14:44 Tainted: [S]=CPU_OUT_OF_SPEC
> 09:14:44 RIP: 0010:memblock_add_range (mm/memblock.c:668)
> 09:14:44 Code: 28 80 3c 01 00 0f 84 04 fd ff ff 4c 89 ef e8 6c 77 09 00 e9 f7 fc ff ff 0f 0b 83 7c 24 1c 00 0f 85 9c fd ff ff e9 c5 fd ff ff <0f> 0b e9 be fd ff ff 44 89 f1 80 e1 07 80 c1 03 38 c1 0f 8c 6b fd
> All code
> ========
> 0: 28 80 3c 01 00 0f sub %al,0xf00013c(%rax)
> 6: 84 04 fd ff ff 4c 89 test %al,-0x76b30001(,%rdi,8)
> d: ef out %eax,(%dx)
> e: e8 6c 77 09 00 call 0x9777f
> 13: e9 f7 fc ff ff jmp 0xfffffffffffffd0f
> 18: 0f 0b ud2
> 1a: 83 7c 24 1c 00 cmpl $0x0,0x1c(%rsp)
> 1f: 0f 85 9c fd ff ff jne 0xfffffffffffffdc1
> 25: e9 c5 fd ff ff jmp 0xfffffffffffffdef
> 2a:* 0f 0b ud2 <-- trapping instruction
> 2c: e9 be fd ff ff jmp 0xfffffffffffffdef
> 31: 44 89 f1 mov %r14d,%ecx
> 34: 80 e1 07 and $0x7,%cl
> 37: 80 c1 03 add $0x3,%cl
> 3a: 38 c1 cmp %al,%cl
> 3c: 0f .byte 0xf
> 3d: 8c 6b fd mov %gs,-0x3(%rbx)
>
> Code starting with the faulting instruction
> ===========================================
> 0: 0f 0b ud2
> 2: e9 be fd ff ff jmp 0xfffffffffffffdc5
> 7: 44 89 f1 mov %r14d,%ecx
> a: 80 e1 07 and $0x7,%cl
> d: 80 c1 03 add $0x3,%cl
> 10: 38 c1 cmp %al,%cl
> 12: 0f .byte 0xf
> 13: 8c 6b fd mov %gs,-0x3(%rbx)
> 09:14:44 RSP: 0000:ffffffff85e07d48 EFLAGS: 00010083 ORIG_RAX: 0000000000000000
> 09:14:44 RAX: 0000000000000020 RBX: 0000000000001c00 RCX: dffffc0000000000
> 09:14:44 RDX: 000000000009f000 RSI: 000000000009d000 RDI: ffffffff8685ebf8
> 09:14:44 RBP: 0000000000000002 R08: 0000000000000020 R09: 0000000000000000
> 09:14:44 R10: ffffffffff200570 R11: fffffbffffe400b2 R12: 000000000009d000
> 09:14:44 R13: 0000000000100000 R14: ffffffff8edf5ce4 R15: ffffffff8edf5ce0
> 09:14:44 FS: 0000000000000000(0000) GS:0000000000000000(0000) knlGS:0000000000000000
> 09:14:44 CR2: ffff888059e2dff8 CR3: 000000005bc1d000 CR4: 00000000000000b0
> 09:14:44 Call Trace:
> 09:14:44 <TASK>
> 09:14:44 ? __memblock_reserve (mm/memblock.c:936)
> 09:14:44 ? add_early_ima_buffer (arch/x86/kernel/setup.c:413)
> 09:14:44 ? parse_setup_data (arch/x86/kernel/setup.c:500)
> 09:14:44 ? setup_arch (arch/x86/kernel/setup.c:245 arch/x86/kernel/setup.c:958)
> 09:14:44 ? start_kernel (init/main.c:922)
> 09:14:44 ? x86_64_start_reservations (arch/x86/kernel/ebda.c:57)
> 09:14:44 ? x86_64_start_kernel (arch/x86/kernel/head64.c:231)
> 09:14:44 ? common_startup_64 (arch/x86/kernel/head_64.S:419)
> 09:14:44 </TASK>
> ....
> Memory: 49640988K/66772816K available (54946K kernel code, 19058K rwdata, 22636K rodata, 2940K init, 120968K bss, 10650188K reserved, 6291456K cma-reserved)
>
> So, there is a memory override, and I am curious about it. Do you think it

Yeah, it seems IMA is reserving a region that overlaps a region reserved
by something else that doesn't use memblock_reserve_kern().

> would be useful to expand this warning to dump more information about the
> issue? (only compiled tested)
>
> if (flags != MEMBLOCK_NONE && flags != rgn->flags) {
> pr_warn("memblock: Flag mismatch at region [%pa-%pa]\n",
> &rgn->base, &rend);
> pr_warn(" Existing region flags: %#x\n", rgn->flags);
> pr_warn(" New range flags: %#x\n", flags);
> pr_warn(" New range: [%pa-%pa]\n", &base, &end);
> WARN_ON_ONCE(1);
> }

I suppose this would be useful. I think enabling memblock debug prints
would also be helpful (using the "memblock=debug" commandline parameter)
if it doesn't impact your production environment too much.

--
Regards,
Pratyush Yadav