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Message-ID: <ef2e7465-5f82-4a8a-9a46-7c070f7560e4@sk.com>
Date: Fri, 17 Jan 2025 14:00:52 +0900
From: Hyeonggon Yoo <hyeonggon.yoo@...com>
To: Bruno Faccini <bfaccini@...dia.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: kernel_team@...ynix.com, 42.hyeyoo@...il.com,
 "linux-mm@...ck.org" <linux-mm@...ck.org>,
 "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
 "rppt@...nel.org" <rppt@...nel.org>, "david@...hat.com" <david@...hat.com>,
 "ziy@...dia.com" <ziy@...dia.com>, "jhubbard@...dia.com"
 <jhubbard@...dia.com>, "mrusiniak@...dia.com" <mrusiniak@...dia.com>
Subject: Re: [fake numa not working][PATCH 1/1] mm/fake-numa: allow later numa
 node hotplug



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@...dia.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.

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;


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