Re: [fake numa not working] [PATCH 1/1] mm/fake-numa: allow later numa node hotplug

Zi Yan
2025-01-17T19:09:27Z

On 17 Jan 2025, at 0:00, Hyeonggon Yoo wrote:

> On 1/6/2025 9:06 PM, Bruno Faccini wrote:
>> Current fake-numa implementation prevents new Numa
>> nodes to be later hot-plugged by drivers.
>> A common symptom of this limitation is the
>> "node <X> was absent from the node_possible_map"
>> message by associated warning in mm/memory_hotplug.c:
>> add_memory_resource().
>> This comes from the lack of remapping in both
>> pxm_to_node_map[] and node_to_pxm_map[] tables
>> to take fake-numa nodes into account and thus
>> triggers collisions with original and physical nodes
>> only-mapping that had been determined from BIOS tables.
>> This patch fixes this by doing the necessary node-ids
>> translation in both pxm_to_node_map[]/node_to_pxm_map[]
>> tables.
>> node_distance[] table has also been fixed accordingly.
>>
>> Signed-off-by: Bruno Faccini <bfaccini@nvidia.com>
>
> Hi Bruno,
>
> This commit causes WARN() and disables fakenuma
> when I pass "numa=fake=4U" on my QEMU setup.
>
> Attaching WARN() log and git bisect log to help debugging.

Is your VM getting 4 NUMA nodes at the end?
Can you also share your QEMU command line and your kernel config?
This can help Bruno reproduce the issue locally. At least, I
cannot reproduce it on mm-everything-2025-01-16-23-18. I also
notice that my VM does not have “No NUMA configuration found”
(in your log) in its kernel log and that might explain
why I could not reproduce it.

Thanks.

>
> Best,
> Hyeonggon
>
> [WARN() splat]
>
> [ 0.009676] No NUMA configuration found
> [ 0.009677] Faking a node at [mem 0x0000000000000000-0x000000083fffffff]
> [ 0.009705] Fake node size 16895MB too small, increasing to 16896MB
> [ 0.009708] Faking node 0 at [mem 0x0000000000001000-0x0000000420000fff] (16896MB)
> [ 0.009711] Faking node 1 at [mem 0x0000000420001000-0x000000083fffffff] (16895MB)
> [ 0.009738] ------------[ cut here ]------------
> [ 0.009739] -1 max nid when expected 1
> [ 0.009760] WARNING: CPU: 0 PID: 0 at drivers/acpi/numa/srat.c:120 fix_pxm_node_maps+0x577/0x810
> [ 0.009766] Modules linked in:
> [ 0.009769] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.13.0-rc6+ #31
> [ 0.009771] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> [ 0.009772] RIP: 0010:fix_pxm_node_maps+0x577/0x810
> [ 0.009774] Code: 8b 85 40 ff ff ff 44 8b 8d 44 ff ff ff 8b 85 48 ff ff ff e9 83 fb ff ff 44 89 f2 44 89 ce 48 c7 c7 aa 2f 84 8d e8 b9 71 01 fe <0f> 0b 41 b8 ff ff ff ff e9 ba fb ff ff 48 c7 c7 a0 d8 d1 8d 44 89
> [ 0.009776] RSP: 0000:ffffffff8da03be0 EFLAGS: 00010046 ORIG_RAX: 0000000000000000
> [ 0.009778] RAX: 0000000000000000 RBX: 0000000000000400 RCX: 0000000000000000
> [ 0.009779] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> [ 0.009780] RBP: ffffffff8da03ca8 R08: 0000000000000000 R09: 0000000000000000
> [ 0.009781] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
> [ 0.009782] R13: 00000000000007ff R14: 0000000000000001 R15: 0000000000000000
> [ 0.009783] FS: 0000000000000000(0000) GS:ffffffff8de8c000(0000) knlGS:0000000000000000
> [ 0.009784] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 0.009785] CR2: ffff90e4bde01000 CR3: 00000001bd03e000 CR4: 00000000000200b0
> [ 0.009788] Call Trace:
> [ 0.009790] <TASK>
> [ 0.009792] ? show_regs+0x71/0x90
> [ 0.009797] ? __warn+0x8d/0x150
> [ 0.009799] ? fix_pxm_node_maps+0x577/0x810
> [ 0.009802] ? report_bug+0x1ab/0x1c0
> [ 0.009805] ? fixup_exception+0x27/0x380
> [ 0.009809] ? early_fixup_exception+0xa2/0xf0
> [ 0.009813] ? do_early_exception+0x28/0x90
> [ 0.009816] ? early_idt_handler_common+0x2f/0x3a
> [ 0.009819] ? fix_pxm_node_maps+0x577/0x810
> [ 0.009822] ? numa_cleanup_meminfo+0x8c/0x5b0
> [ 0.009828] numa_emulation+0x4e3/0xad0
> [ 0.009830] ? __pfx_dummy_numa_init+0x10/0x10
> [ 0.009833] ? __pfx_dummy_numa_init+0x10/0x10
> [ 0.009836] numa_memblks_init+0x10c/0x2c0
> [ 0.009838] ? __pfx_dummy_numa_init+0x10/0x10
> [ 0.009840] numa_init+0x61/0x3e0
> [ 0.009842] ? topology_register_boot_apic+0x2a/0x40
> [ 0.009846] x86_numa_init+0x65/0x80
> [ 0.009848] initmem_init+0xe/0x20
> [ 0.009850] setup_arch+0x9d8/0xfa0
> [ 0.009852] ? _printk+0x58/0x90
> [ 0.009855] start_kernel+0x5f/0xb50
> [ 0.009860] x86_64_start_reservations+0x18/0x30
> [ 0.009863] x86_64_start_kernel+0xc0/0x110
> [ 0.009864] ? setup_ghcb+0xe/0x140
> [ 0.009867] common_startup_64+0x13e/0x141
> [ 0.009871] </TASK>
> [ 0.009871] ---[ end trace 0000000000000000 ]---
>
> [Git bisect log]
>
> # bad: [f378252a2168c2fbf8fc08b635061e5f6748c1f2] kasan: sw_tags: use str_on_off() helper in kasan_init_sw_tags()
> git bisect bad f378252a2168c2fbf8fc08b635061e5f6748c1f2
> # good: [cbc5dde0a461240046e8a41c43d7c3b76d5db952] fs/proc: fix softlockup in __read_vmcore (part 2)
> git bisect good cbc5dde0a461240046e8a41c43d7c3b76d5db952
> # good: [fb73203263021f2ee9dd54d280b1c543d10acd76] mm: move common part of pagetable_*_ctor to helper
> git bisect good fb73203263021f2ee9dd54d280b1c543d10acd76
> # bad: [8fd966c9310f14d5bbe653cf087853582170aad6] mm, swap: remove old allocation path for HDD
> git bisect bad 8fd966c9310f14d5bbe653cf087853582170aad6
> # bad: [8646971f02651146554233d63fdd721f5f060973] mm: shmem: skip swapcache for swapin of synchronous swap device
> git bisect bad 8646971f02651146554233d63fdd721f5f060973
> # good: [b8ba614eaa8dd31702c61e7df7231b1b18b99259] mm/damon/paddr: report filter-passed bytes back for DAMOS_STAT action
> git bisect good b8ba614eaa8dd31702c61e7df7231b1b18b99259
> # good: [fd0935b8e9e8c2edf05a3d0ffa09d0aa3e9cf2dd] Docs/ABI/damon: document per-region DAMOS filter-passed bytes stat file
> git bisect good fd0935b8e9e8c2edf05a3d0ffa09d0aa3e9cf2dd
> # good: [3ffd3cd7e2e8793d3b5fbb83c03668c47ab6d599] selftests/damon: remove tests for DAMON debugfs interface
> git bisect good 3ffd3cd7e2e8793d3b5fbb83c03668c47ab6d599
> # good: [bf9f93f0b7bff8af780330f5094775a39caf3612] mm/damon: remove DAMON debugfs interface
> git bisect good bf9f93f0b7bff8af780330f5094775a39caf3612
> # bad: [1746744be6ff271e29345a5be4cc144aa33b10ab] mm/memmap: prevent double scanning of memmap by kmemleak
> git bisect bad 1746744be6ff271e29345a5be4cc144aa33b10ab
> # bad: [ca19a5ab8756ef78c34d02d2b8c266a9cc7bf57d] mm/fake-numa: allow later numa node hotplug
> git bisect bad ca19a5ab8756ef78c34d02d2b8c266a9cc7bf57d
> # first bad commit: [ca19a5ab8756ef78c34d02d2b8c266a9cc7bf57d] mm/fake-numa: allow later numa node hotplug
>
>> ---
>> drivers/acpi/numa/srat.c | 86 ++++++++++++++++++++++++++++++++++++
>> include/acpi/acpi_numa.h | 5 +++
>> include/linux/numa_memblks.h | 3 ++
>> mm/numa_emulation.c | 45 ++++++++++++++++---
>> mm/numa_memblks.c | 2 +-
>> 5 files changed, 133 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/acpi/numa/srat.c b/drivers/acpi/numa/srat.c
>> index bec0dcd1f9c3..59fffe34c9d0 100644
>> --- a/drivers/acpi/numa/srat.c
>> +++ b/drivers/acpi/numa/srat.c
>> @@ -81,6 +81,92 @@ int acpi_map_pxm_to_node(int pxm)
>> }
>> EXPORT_SYMBOL(acpi_map_pxm_to_node);
>> +#ifdef CONFIG_NUMA_EMU
>> +/*
>> + * Take max_nid - 1 fake-numa nodes into account in both
>> + * pxm_to_node_map()/node_to_pxm_map[] tables.
>> + */
>> +int __init fix_pxm_node_maps(int max_nid)
>> +{
>> + static int pxm_to_node_map_copy[MAX_PXM_DOMAINS] __initdata
>> + = { [0 ... MAX_PXM_DOMAINS - 1] = NUMA_NO_NODE };
>> + static int node_to_pxm_map_copy[MAX_NUMNODES] __initdata
>> + = { [0 ... MAX_NUMNODES - 1] = PXM_INVAL };
>> + int i, j, index = -1, count = 0;
>> + nodemask_t nodes_to_enable;
>> +
>> + if (numa_off || srat_disabled())
>> + return -1;
>> +
>> + /* find fake nodes PXM mapping */
>> + for (i = 0; i < MAX_NUMNODES; i++) {
>> + if (node_to_pxm_map[i] != PXM_INVAL) {
>> + for (j = 0; j <= max_nid; j++) {
>> + if ((emu_nid_to_phys[j] == i) &&
>> + WARN(node_to_pxm_map_copy[j] != PXM_INVAL,
>> + "Node %d is already binded to PXM %d\n",
>> + j, node_to_pxm_map_copy[j]))
>> + return -1;
>> + if (emu_nid_to_phys[j] == i) {
>> + node_to_pxm_map_copy[j] =
>> + node_to_pxm_map[i];
>> + if (j > index)
>> + index = j;
>> + count++;
>> + }
>> + }
>> + }
>> + }
>> + if (WARN(index != max_nid, "%d max nid when expected %d\n",
>> + index, max_nid))
>> + return -1;
>> +
>> + nodes_clear(nodes_to_enable);
>> +
>> + /* map phys nodes not used for fake nodes */
>> + for (i = 0; i < MAX_NUMNODES; i++) {
>> + if (node_to_pxm_map[i] != PXM_INVAL) {
>> + for (j = 0; j <= max_nid; j++)
>> + if (emu_nid_to_phys[j] == i)
>> + break;
>> + /* fake nodes PXM mapping has been done */
>> + if (j <= max_nid)
>> + continue;
>> + /* find first hole */
>> + for (j = 0;
>> + j < MAX_NUMNODES &&
>> + node_to_pxm_map_copy[j] != PXM_INVAL;
>> + j++)
>> + ;
>> + if (WARN(j == MAX_NUMNODES,
>> + "Number of nodes exceeds MAX_NUMNODES\n"))
>> + return -1;
>> + node_to_pxm_map_copy[j] = node_to_pxm_map[i];
>> + node_set(j, nodes_to_enable);
>> + count++;
>> + }
>> + }
>> +
>> + /* creating reverse mapping in pxm_to_node_map[] */
>> + for (i = 0; i < MAX_NUMNODES; i++)
>> + if (node_to_pxm_map_copy[i] != PXM_INVAL &&
>> + pxm_to_node_map_copy[node_to_pxm_map_copy[i]] == NUMA_NO_NODE)
>> + pxm_to_node_map_copy[node_to_pxm_map_copy[i]] = i;
>> +
>> + /* overwrite with new mapping */
>> + for (i = 0; i < MAX_NUMNODES; i++) {
>> + node_to_pxm_map[i] = node_to_pxm_map_copy[i];
>> + pxm_to_node_map[i] = pxm_to_node_map_copy[i];
>> + }
>> +
>> + /* enable other nodes found in PXM for hotplug */
>> + nodes_or(numa_nodes_parsed, nodes_to_enable, numa_nodes_parsed);
>> +
>> + pr_debug("found %d total number of nodes\n", count);
>> + return 0;
>> +}
>> +#endif
>> +
>> static void __init
>> acpi_table_print_srat_entry(struct acpi_subtable_header *header)
>> {
>> diff --git a/include/acpi/acpi_numa.h b/include/acpi/acpi_numa.h
>> index b5f594754a9e..99b960bd473c 100644
>> --- a/include/acpi/acpi_numa.h
>> +++ b/include/acpi/acpi_numa.h
>> @@ -17,11 +17,16 @@ extern int node_to_pxm(int);
>> extern int acpi_map_pxm_to_node(int);
>> extern unsigned char acpi_srat_revision;
>> extern void disable_srat(void);
>> +extern int fix_pxm_node_maps(int max_nid);
>> extern void bad_srat(void);
>> extern int srat_disabled(void);
>> #else /* CONFIG_ACPI_NUMA */
>> +static inline int fix_pxm_node_maps(int max_nid)
>> +{
>> + return 0;
>> +}
>> static inline void disable_srat(void)
>> {
>> }
>> diff --git a/include/linux/numa_memblks.h b/include/linux/numa_memblks.h
>> index cfad6ce7e1bd..dd85613cdd86 100644
>> --- a/include/linux/numa_memblks.h
>> +++ b/include/linux/numa_memblks.h
>> @@ -29,7 +29,10 @@ int __init numa_cleanup_meminfo(struct numa_meminfo *mi);
>> int __init numa_memblks_init(int (*init_func)(void),
>> bool memblock_force_top_down);
>> +extern int numa_distance_cnt;
>> +
>> #ifdef CONFIG_NUMA_EMU
>> +extern int emu_nid_to_phys[MAX_NUMNODES];
>> int numa_emu_cmdline(char *str);
>> void __init numa_emu_update_cpu_to_node(int *emu_nid_to_phys,
>> unsigned int nr_emu_nids);
>> diff --git a/mm/numa_emulation.c b/mm/numa_emulation.c
>> index 031fb9961bf7..9d55679d99ce 100644
>> --- a/mm/numa_emulation.c
>> +++ b/mm/numa_emulation.c
>> @@ -8,11 +8,12 @@
>> #include <linux/memblock.h>
>> #include <linux/numa_memblks.h>
>> #include <asm/numa.h>
>> +#include <acpi/acpi_numa.h>
>> #define FAKE_NODE_MIN_SIZE ((u64)32 << 20)
>> #define FAKE_NODE_MIN_HASH_MASK (~(FAKE_NODE_MIN_SIZE - 1UL))
>> -static int emu_nid_to_phys[MAX_NUMNODES];
>> +int emu_nid_to_phys[MAX_NUMNODES];
>> static char *emu_cmdline __initdata;
>> int __init numa_emu_cmdline(char *str)
>> @@ -379,6 +380,7 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
>> size_t phys_size = numa_dist_cnt * numa_dist_cnt * sizeof(phys_dist[0]);
>> int max_emu_nid, dfl_phys_nid;
>> int i, j, ret;
>> + nodemask_t physnode_mask = numa_nodes_parsed;
>> if (!emu_cmdline)
>> goto no_emu;
>> @@ -395,7 +397,6 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
>> * split the system RAM into N fake nodes.
>> */
>> if (strchr(emu_cmdline, 'U')) {
>> - nodemask_t physnode_mask = numa_nodes_parsed;
>> unsigned long n;
>> int nid = 0;
>> @@ -465,9 +466,6 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
>> */
>> max_emu_nid = setup_emu2phys_nid(&dfl_phys_nid);
>> - /* commit */
>> - *numa_meminfo = ei;
>> -
>> /* Make sure numa_nodes_parsed only contains emulated nodes */
>> nodes_clear(numa_nodes_parsed);
>> for (i = 0; i < ARRAY_SIZE(ei.blk); i++)
>> @@ -475,10 +473,21 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
>> ei.blk[i].nid != NUMA_NO_NODE)
>> node_set(ei.blk[i].nid, numa_nodes_parsed);
>> - numa_emu_update_cpu_to_node(emu_nid_to_phys, ARRAY_SIZE(emu_nid_to_phys));
>> + /* fix pxm_to_node_map[] and node_to_pxm_map[] to avoid collision
>> + * with faked numa nodes, particularly during later memory hotplug
>> + * handling, and also update numa_nodes_parsed accordingly.
>> + */
>> + ret = fix_pxm_node_maps(max_emu_nid);
>> + if (ret < 0)
>> + goto no_emu;
>> +
>> + /* commit */
>> + *numa_meminfo = ei;
>> +
>> + numa_emu_update_cpu_to_node(emu_nid_to_phys, max_emu_nid + 1);
>> /* make sure all emulated nodes are mapped to a physical node */
>> - for (i = 0; i < ARRAY_SIZE(emu_nid_to_phys); i++)
>> + for (i = 0; i < max_emu_nid + 1; i++)
>> if (emu_nid_to_phys[i] == NUMA_NO_NODE)
>> emu_nid_to_phys[i] = dfl_phys_nid;
>> @@ -501,12 +510,34 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
>> numa_set_distance(i, j, dist);
>> }
>> }
>> + for (i = 0; i < numa_distance_cnt; i++) {
>> + for (j = 0; j < numa_distance_cnt; j++) {
>> + int physi, physj;
>> + u8 dist;
>> +
>> + /* distance between fake nodes is already ok */
>> + if (emu_nid_to_phys[i] != NUMA_NO_NODE &&
>> + emu_nid_to_phys[j] != NUMA_NO_NODE)
>> + continue;
>> + if (emu_nid_to_phys[i] != NUMA_NO_NODE)
>> + physi = emu_nid_to_phys[i];
>> + else
>> + physi = i - max_emu_nid;
>> + if (emu_nid_to_phys[j] != NUMA_NO_NODE)
>> + physj = emu_nid_to_phys[j];
>> + else
>> + physj = j - max_emu_nid;
>> + dist = phys_dist[physi * numa_dist_cnt + physj];
>> + numa_set_distance(i, j, dist);
>> + }
>> + }
>> /* free the copied physical distance table */
>> memblock_free(phys_dist, phys_size);
>> return;
>> no_emu:
>> + numa_nodes_parsed = physnode_mask;
>> /* No emulation. Build identity emu_nid_to_phys[] for numa_add_cpu() */
>> for (i = 0; i < ARRAY_SIZE(emu_nid_to_phys); i++)
>> emu_nid_to_phys[i] = i;
>> diff --git a/mm/numa_memblks.c b/mm/numa_memblks.c
>> index a3877e9bc878..ff4054f4334d 100644
>> --- a/mm/numa_memblks.c
>> +++ b/mm/numa_memblks.c
>> @@ -7,7 +7,7 @@
>> #include <linux/numa.h>
>> #include <linux/numa_memblks.h>
>> -static int numa_distance_cnt;
>> +int numa_distance_cnt;
>> static u8 *numa_distance;
>> nodemask_t numa_nodes_parsed __initdata;

Best Regards,
Yan, Zi