Message-Id: <20191224085544.24960-1-greentime.hu@sifive.com>
Date:   Tue, 24 Dec 2019 16:55:44 +0800
From:   Greentime Hu <greentime.hu@...ive.com>
To:     greentime.hu@...ive.com, green.hu@...il.com, greentime@...nel.org,
        paul.walmsley@...ive.com, palmer@...belt.com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH] riscv: Add numa support for riscv64 platform

This implementation is based on arm64 porting. It is tested with
qemu-system-riscv64, unleashed board and OmniXtend FPGA platform.

There will be 2 nodes in /sys/devices/system/node if it is described in dts and
CONFIG_NUMA is enabled. We can use numastat/numactl/numademo to see its status.

Signed-off-by: Greentime Hu <greentime.hu@...ive.com>
---
 arch/riscv/Kconfig               |  30 ++-
 arch/riscv/include/asm/mmzone.h  |  13 ++
 arch/riscv/include/asm/numa.h    |  46 ++++
 arch/riscv/include/asm/pci.h     |  10 +
 arch/riscv/include/asm/pgtable.h |  20 ++
 arch/riscv/kernel/setup.c        |  26 ++-
 arch/riscv/kernel/smpboot.c      |  20 +-
 arch/riscv/mm/Makefile           |   1 +
 arch/riscv/mm/init.c             |   3 +
 arch/riscv/mm/numa.c             | 372 +++++++++++++++++++++++++++++++
 10 files changed, 536 insertions(+), 5 deletions(-)
 create mode 100644 arch/riscv/include/asm/mmzone.h
 create mode 100644 arch/riscv/include/asm/numa.h
 create mode 100644 arch/riscv/mm/numa.c

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index bc7598fc5f00..53ae1816df50 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -22,7 +22,6 @@ config RISCV
 	select CLONE_BACKWARDS
 	select COMMON_CLK
 	select GENERIC_CLOCKEVENTS
-	select GENERIC_CPU_DEVICES
 	select GENERIC_IRQ_SHOW
 	select GENERIC_PCI_IOMAP
 	select GENERIC_SCHED_CLOCK
@@ -234,6 +233,35 @@ config TUNE_GENERIC
 	bool "generic"
 
 endchoice
+# Common NUMA Features
+config NUMA
+	bool "Numa Memory Allocation and Scheduler Support"
+	select OF_NUMA
+	select ARCH_SUPPORTS_NUMA_BALANCING
+	depends on SPARSEMEM
+	help
+	  Enable NUMA (Non Uniform Memory Access) support.
+
+	  The kernel will try to allocate memory used by a CPU on the
+	  local memory of the CPU and add some more
+	  NUMA awareness to the kernel.
+
+config NODES_SHIFT
+	int "Maximum NUMA Nodes (as a power of 2)"
+	range 1 10
+	default "2"
+	depends on NEED_MULTIPLE_NODES
+	help
+	  Specify the maximum number of NUMA Nodes available on the target
+	  system.  Increases memory reserved to accommodate various tables.
+
+config USE_PERCPU_NUMA_NODE_ID
+	def_bool y
+	depends on NUMA
+
+config NEED_PER_CPU_EMBED_FIRST_CHUNK
+	def_bool y
+	depends on NUMA
 
 config RISCV_ISA_C
 	bool "Emit compressed instructions when building Linux"
diff --git a/arch/riscv/include/asm/mmzone.h b/arch/riscv/include/asm/mmzone.h
new file mode 100644
index 000000000000..fa17e01d9ab2
--- /dev/null
+++ b/arch/riscv/include/asm/mmzone.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_MMZONE_H
+#define __ASM_MMZONE_H
+
+#ifdef CONFIG_NUMA
+
+#include <asm/numa.h>
+
+extern struct pglist_data *node_data[];
+#define NODE_DATA(nid)		(node_data[(nid)])
+
+#endif /* CONFIG_NUMA */
+#endif /* __ASM_MMZONE_H */
diff --git a/arch/riscv/include/asm/numa.h b/arch/riscv/include/asm/numa.h
new file mode 100644
index 000000000000..10a4513d078b
--- /dev/null
+++ b/arch/riscv/include/asm/numa.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_NUMA_H
+#define __ASM_NUMA_H
+
+#include <asm/topology.h>
+
+#ifdef CONFIG_NUMA
+
+extern nodemask_t numa_nodes_parsed __initdata;
+
+extern bool numa_off;
+
+/* Mappings between node number and cpus on that node. */
+extern cpumask_var_t node_to_cpumask_map[MAX_NUMNODES];
+void numa_clear_node(unsigned int cpu);
+
+#ifdef CONFIG_DEBUG_PER_CPU_MAPS
+const struct cpumask *cpumask_of_node(int node);
+#else
+/* Returns a pointer to the cpumask of CPUs on Node 'node'. */
+static inline const struct cpumask *cpumask_of_node(int node)
+{
+	return node_to_cpumask_map[node];
+}
+#endif
+
+void __init riscv_numa_init(void);
+int __init numa_add_memblk(int nodeid, u64 start, u64 end);
+void __init numa_set_distance(int from, int to, int distance);
+void __init numa_free_distance(void);
+void __init early_map_cpu_to_node(unsigned int cpu, int nid);
+void numa_store_cpu_info(unsigned int cpu);
+void numa_add_cpu(unsigned int cpu);
+void numa_remove_cpu(unsigned int cpu);
+
+#else	/* CONFIG_NUMA */
+
+static inline void numa_store_cpu_info(unsigned int cpu) { }
+static inline void numa_add_cpu(unsigned int cpu) { }
+static inline void numa_remove_cpu(unsigned int cpu) { }
+static inline void riscv_numa_init(void) { }
+static inline void early_map_cpu_to_node(unsigned int cpu, int nid) { }
+
+#endif	/* CONFIG_NUMA */
+
+#endif	/* __ASM_NUMA_H */
diff --git a/arch/riscv/include/asm/pci.h b/arch/riscv/include/asm/pci.h
index 5ac8daa1cc36..781aa8b6dcd3 100644
--- a/arch/riscv/include/asm/pci.h
+++ b/arch/riscv/include/asm/pci.h
@@ -32,6 +32,16 @@ static inline int pci_proc_domain(struct pci_bus *bus)
 	/* always show the domain in /proc */
 	return 1;
 }
+
+#ifdef	CONFIG_NUMA
+int pcibus_to_node(struct pci_bus *bus);
+#ifndef cpumask_of_pcibus
+#define cpumask_of_pcibus(bus)	(pcibus_to_node(bus) == -1 ?		\
+				 cpu_all_mask :				\
+				 cpumask_of_node(pcibus_to_node(bus)))
+#endif
+#endif	/* CONFIG_NUMA */
+
 #endif  /* CONFIG_PCI */
 
 #endif  /* __ASM_PCI_H */
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index d3221017194d..04b7c38870f7 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -175,6 +175,11 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd)
 	return (unsigned long)pfn_to_virt(pmd_val(pmd) >> _PAGE_PFN_SHIFT);
 }
 
+static inline pte_t pmd_pte(pmd_t pmd)
+{
+	return __pte(pmd_val(pmd));
+}
+
 /* Yields the page frame number (PFN) of a page table entry */
 static inline unsigned long pte_pfn(pte_t pte)
 {
@@ -288,6 +293,21 @@ static inline pte_t pte_mkhuge(pte_t pte)
 	return pte;
 }
 
+#ifdef CONFIG_NUMA_BALANCING
+/*
+ * See the comment in include/asm-generic/pgtable.h
+ */
+static inline int pte_protnone(pte_t pte)
+{
+	return (pte_val(pte) & (_PAGE_PRESENT | _PAGE_PROT_NONE)) == _PAGE_PROT_NONE;
+}
+
+static inline int pmd_protnone(pmd_t pmd)
+{
+	return pte_protnone(pmd_pte(pmd));
+}
+#endif
+
 /* Modify page protection bits */
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 845ae0e12115..f6f2354036a0 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -53,6 +53,31 @@ void __init parse_dtb(void)
 #endif
 }
 
+static DEFINE_PER_CPU(struct cpu, cpu_devices);
+
+static int __init topology_init(void)
+{
+	int i, ret;
+
+#ifdef CONFIG_NEED_MULTIPLE_NODES
+	for_each_online_node(i)
+		register_one_node(i);
+#endif
+
+	for_each_possible_cpu(i) {
+		struct cpu *cpu = &per_cpu(cpu_devices, i);
+
+		cpu->hotpluggable = 1;
+		ret = register_cpu(cpu, i);
+		if (unlikely(ret))
+			pr_warn("Warning: %s: register_cpu %d failed (%d)\n",
+			       __func__, i, ret);
+	}
+
+	return 0;
+}
+subsys_initcall(topology_init);
+
 void __init setup_arch(char **cmdline_p)
 {
 	init_mm.start_code = (unsigned long) _stext;
@@ -66,7 +91,6 @@ void __init setup_arch(char **cmdline_p)
 
 	setup_bootmem();
 	paging_init();
-	unflatten_device_tree();
 
 #ifdef CONFIG_SWIOTLB
 	swiotlb_init(1);
diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index 261f4087cc39..bcb67ac403e4 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -26,6 +26,7 @@
 #include <linux/sched/mm.h>
 #include <asm/irq.h>
 #include <asm/mmu_context.h>
+#include <asm/numa.h>
 #include <asm/tlbflush.h>
 #include <asm/sections.h>
 #include <asm/sbi.h>
@@ -45,6 +46,11 @@ void __init smp_prepare_boot_cpu(void)
 void __init smp_prepare_cpus(unsigned int max_cpus)
 {
 	int cpuid;
+	unsigned int this_cpu;
+
+	this_cpu = smp_processor_id();
+	numa_store_cpu_info(this_cpu);
+	numa_add_cpu(this_cpu);
 
 	/* This covers non-smp usecase mandated by "nosmp" option */
 	if (max_cpus == 0)
@@ -54,6 +60,7 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 		if (cpuid == smp_processor_id())
 			continue;
 		set_cpu_present(cpuid, true);
+		numa_store_cpu_info(cpuid);
 	}
 }
 
@@ -72,6 +79,7 @@ void __init setup_smp(void)
 		if (hart == cpuid_to_hartid_map(0)) {
 			BUG_ON(found_boot_cpu);
 			found_boot_cpu = 1;
+			early_map_cpu_to_node(0, of_node_to_nid(dn));
 			continue;
 		}
 		if (cpuid >= NR_CPUS) {
@@ -81,6 +89,7 @@ void __init setup_smp(void)
 		}
 
 		cpuid_to_hartid_map(cpuid) = hart;
+		early_map_cpu_to_node(cpuid, of_node_to_nid(dn));
 		cpuid++;
 	}
 
@@ -136,15 +145,20 @@ void __init smp_cpus_done(unsigned int max_cpus)
 asmlinkage __visible void __init smp_callin(void)
 {
 	struct mm_struct *mm = &init_mm;
+	unsigned int this_cpu;
+
+	this_cpu = smp_processor_id();
 
 	/* All kernel threads share the same mm context.  */
 	mmgrab(mm);
 	current->active_mm = mm;
 
 	trap_init();
-	notify_cpu_starting(smp_processor_id());
-	update_siblings_masks(smp_processor_id());
-	set_cpu_online(smp_processor_id(), 1);
+	notify_cpu_starting(this_cpu);
+	numa_store_cpu_info(this_cpu);
+	numa_add_cpu(this_cpu);
+	update_siblings_masks(this_cpu);
+	set_cpu_online(this_cpu, true);
 	/*
 	 * Remote TLB flushes are ignored while the CPU is offline, so emit
 	 * a local TLB flush right now just in case.
diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
index 9d9a17335686..59c956c0b0d0 100644
--- a/arch/riscv/mm/Makefile
+++ b/arch/riscv/mm/Makefile
@@ -17,3 +17,4 @@ ifeq ($(CONFIG_MMU),y)
 obj-$(CONFIG_SMP) += tlbflush.o
 endif
 obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
+obj-$(CONFIG_NUMA)         += numa.o
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 573463d1c799..17c749744e05 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -18,6 +18,7 @@
 #include <asm/sections.h>
 #include <asm/pgtable.h>
 #include <asm/io.h>
+#include <asm/numa.h>
 
 #include "../kernel/head.h"
 
@@ -453,6 +454,8 @@ static void __init setup_vm_final(void)
 void __init paging_init(void)
 {
 	setup_vm_final();
+	unflatten_device_tree();
+	riscv_numa_init();
 	memblocks_present();
 	sparse_init();
 	setup_zero_page();
diff --git a/arch/riscv/mm/numa.c b/arch/riscv/mm/numa.c
new file mode 100644
index 000000000000..b679b2831990
--- /dev/null
+++ b/arch/riscv/mm/numa.c
@@ -0,0 +1,372 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * NUMA support, based on the arm64 implementation.
+ *
+ * Copyright (C) 2015 Cavium Inc.
+ * Author: Ganapatrao Kulkarni <gkulkarni@...ium.com>
+ * Copyright (C) 2019 SiFive, Inc
+ */
+
+#define pr_fmt(fmt) "NUMA: " fmt
+
+#include <linux/memblock.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/device.h>
+#include <linux/pci.h>
+
+struct pglist_data *node_data[MAX_NUMNODES] __read_mostly;
+EXPORT_SYMBOL(node_data);
+nodemask_t numa_nodes_parsed __initdata;
+static int cpu_to_node_map[NR_CPUS] = { [0 ... NR_CPUS-1] = NUMA_NO_NODE };
+
+static u8 *numa_distance;
+static int numa_distance_cnt;
+bool numa_off;
+
+static __init int numa_parse_early_param(char *opt)
+{
+	if (!opt)
+		return -EINVAL;
+	if (str_has_prefix(opt, "off"))
+		numa_off = true;
+
+	return 0;
+}
+early_param("numa", numa_parse_early_param);
+
+cpumask_var_t node_to_cpumask_map[MAX_NUMNODES];
+EXPORT_SYMBOL(node_to_cpumask_map);
+
+#ifdef CONFIG_DEBUG_PER_CPU_MAPS
+
+/*
+ * Returns a pointer to the bitmask of CPUs on Node 'node'.
+ */
+const struct cpumask *cpumask_of_node(int node)
+{
+	if (WARN_ON(node >= nr_node_ids))
+		return cpu_none_mask;
+
+	if (WARN_ON(node_to_cpumask_map[node] == NULL))
+		return cpu_online_mask;
+
+	return node_to_cpumask_map[node];
+}
+EXPORT_SYMBOL(cpumask_of_node);
+
+#endif
+
+int pcibus_to_node(struct pci_bus *bus)
+{
+	return dev_to_node(&bus->dev);
+}
+EXPORT_SYMBOL(pcibus_to_node);
+
+static void numa_update_cpu(unsigned int cpu, bool remove)
+{
+	int nid = cpu_to_node(cpu);
+
+	if (nid == NUMA_NO_NODE)
+		return;
+
+	if (remove)
+		cpumask_clear_cpu(cpu, node_to_cpumask_map[nid]);
+	else
+		cpumask_set_cpu(cpu, node_to_cpumask_map[nid]);
+}
+
+void numa_add_cpu(unsigned int cpu)
+{
+	numa_update_cpu(cpu, false);
+}
+
+/*
+ * Set the cpu to node and mem mapping
+ */
+void numa_store_cpu_info(unsigned int cpu)
+{
+	set_cpu_numa_node(cpu, cpu_to_node_map[cpu]);
+}
+
+void __init early_map_cpu_to_node(unsigned int cpu, int nid)
+{
+	/* fallback to node 0 */
+	if (nid < 0 || nid >= MAX_NUMNODES || numa_off)
+		nid = 0;
+
+	cpu_to_node_map[cpu] = nid;
+
+	/*
+	 * We should set the numa node of cpu0 as soon as possible, because it
+	 * has already been set up online before. cpu_to_node(0) will soon be
+	 * called.
+	 */
+	if (!cpu)
+		set_cpu_numa_node(cpu, nid);
+}
+
+static int __init numa_alloc_distance(void)
+{
+	size_t size;
+	u64 phys;
+	int i, j;
+
+	size = nr_node_ids * nr_node_ids * sizeof(numa_distance[0]);
+	phys = memblock_find_in_range(0, PFN_PHYS(max_pfn),
+				      size, PAGE_SIZE);
+	if (WARN_ON(!phys))
+		return -ENOMEM;
+
+	memblock_reserve(phys, size);
+
+	numa_distance = __va(phys);
+	numa_distance_cnt = nr_node_ids;
+
+	/* fill with the default distances */
+	for (i = 0; i < numa_distance_cnt; i++)
+		for (j = 0; j < numa_distance_cnt; j++)
+			numa_distance[i * numa_distance_cnt + j] = i == j ?
+				LOCAL_DISTANCE : REMOTE_DISTANCE;
+
+	pr_debug("Initialized distance table, cnt=%d\n", numa_distance_cnt);
+
+	return 0;
+}
+
+/**
+ * numa_add_memblk() - Set node id to memblk
+ * @nid: NUMA node ID of the new memblk
+ * @start: Start address of the new memblk
+ * @end:  End address of the new memblk
+ *
+ * RETURNS:
+ * 0 on success, -errno on failure.
+ */
+int __init numa_add_memblk(int nid, u64 start, u64 end)
+{
+	int ret;
+
+	ret = memblock_set_node(start, (end - start), &memblock.memory, nid);
+	if (ret < 0) {
+		pr_err("memblock [0x%llx - 0x%llx] failed to add on node %d\n",
+			start, (end - 1), nid);
+		return ret;
+	}
+
+	node_set(nid, numa_nodes_parsed);
+	return ret;
+}
+
+/*
+ * Initialize NODE_DATA for a node on the local memory
+ */
+static void __init setup_node_data(int nid, u64 start_pfn, u64 end_pfn)
+{
+	const size_t nd_size = roundup(sizeof(pg_data_t), SMP_CACHE_BYTES);
+	u64 nd_pa;
+	void *nd;
+	int tnid;
+
+	if (start_pfn >= end_pfn)
+		pr_info("Initmem setup node %d [<memory-less node>]\n", nid);
+
+	nd_pa = memblock_phys_alloc_try_nid(nd_size, SMP_CACHE_BYTES, nid);
+	if (!nd_pa)
+		panic("Cannot allocate %zu bytes for node %d data\n",
+		      nd_size, nid);
+
+	nd = __va(nd_pa);
+
+	/* report and initialize */
+	pr_info("NODE_DATA [mem %#010Lx-%#010Lx]\n",
+		nd_pa, nd_pa + nd_size - 1);
+	tnid = early_pfn_to_nid(nd_pa >> PAGE_SHIFT);
+	if (tnid != nid)
+		pr_info("NODE_DATA(%d) on node %d\n", nid, tnid);
+
+	node_data[nid] = nd;
+	memset(NODE_DATA(nid), 0, sizeof(pg_data_t));
+	NODE_DATA(nid)->node_id = nid;
+	NODE_DATA(nid)->node_start_pfn = start_pfn;
+	NODE_DATA(nid)->node_spanned_pages = end_pfn - start_pfn;
+}
+
+void __init numa_set_distance(int from, int to, int distance)
+{
+	if (!numa_distance) {
+		pr_warn_once("Warning: distance table not allocated yet\n");
+		return;
+	}
+
+	if (from >= numa_distance_cnt || to >= numa_distance_cnt ||
+			from < 0 || to < 0) {
+		pr_warn_once("Warning: node ids are out of bound, from=%d to=%d distance=%d\n",
+			    from, to, distance);
+		return;
+	}
+
+	if ((u8)distance != distance ||
+	    (from == to && distance != LOCAL_DISTANCE)) {
+		pr_warn_once("Warning: invalid distance parameter, from=%d to=%d distance=%d\n",
+			     from, to, distance);
+		return;
+	}
+
+	numa_distance[from * numa_distance_cnt + to] = distance;
+}
+
+/*
+ * Return NUMA distance @from to @to
+ */
+int __node_distance(int from, int to)
+{
+	if (from >= numa_distance_cnt || to >= numa_distance_cnt)
+		return from == to ? LOCAL_DISTANCE : REMOTE_DISTANCE;
+	return numa_distance[from * numa_distance_cnt + to];
+}
+EXPORT_SYMBOL(__node_distance);
+
+static int __init numa_register_nodes(void)
+{
+	int nid;
+	struct memblock_region *mblk;
+
+	/* Check that valid nid is set to memblks */
+	for_each_memblock(memory, mblk)
+		if (mblk->nid == NUMA_NO_NODE || mblk->nid >= MAX_NUMNODES) {
+			pr_warn("Warning: invalid memblk node %d [mem %#010Lx-%#010Lx]\n",
+				mblk->nid, mblk->base,
+				mblk->base + mblk->size - 1);
+			return -EINVAL;
+		}
+
+	/* Finally register nodes. */
+	for_each_node_mask(nid, numa_nodes_parsed) {
+		unsigned long start_pfn, end_pfn;
+
+		get_pfn_range_for_nid(nid, &start_pfn, &end_pfn);
+		setup_node_data(nid, start_pfn, end_pfn);
+		node_set_online(nid);
+	}
+
+	/* Setup online nodes to actual nodes*/
+	node_possible_map = numa_nodes_parsed;
+
+	return 0;
+}
+static void __init setup_node_to_cpumask_map(void)
+{
+	int node;
+
+	/* setup nr_node_ids if not done yet */
+	if (nr_node_ids == MAX_NUMNODES)
+		setup_nr_node_ids();
+
+	/* allocate and clear the mapping */
+	for (node = 0; node < nr_node_ids; node++) {
+		alloc_bootmem_cpumask_var(&node_to_cpumask_map[node]);
+		cpumask_clear(node_to_cpumask_map[node]);
+	}
+
+	/* cpumask_of_node() will now work */
+	pr_debug("Node to cpumask map for %u nodes\n", nr_node_ids);
+}
+
+void __init numa_free_distance(void)
+{
+	size_t size;
+
+	if (!numa_distance)
+		return;
+
+	size = numa_distance_cnt * numa_distance_cnt *
+		sizeof(numa_distance[0]);
+
+	memblock_free(__pa(numa_distance), size);
+	numa_distance_cnt = 0;
+	numa_distance = NULL;
+}
+static int __init numa_init(int (*init_func)(void))
+{
+	int ret;
+
+	nodes_clear(numa_nodes_parsed);
+	nodes_clear(node_possible_map);
+	nodes_clear(node_online_map);
+
+	ret = numa_alloc_distance();
+	if (ret < 0)
+		return ret;
+
+	ret = init_func();
+	if (ret < 0)
+		goto out_free_distance;
+
+	if (nodes_empty(numa_nodes_parsed)) {
+		pr_info("No NUMA configuration found\n");
+		ret = -EINVAL;
+		goto out_free_distance;
+	}
+
+	ret = numa_register_nodes();
+	if (ret < 0)
+		goto out_free_distance;
+
+	setup_node_to_cpumask_map();
+
+	return 0;
+out_free_distance:
+	numa_free_distance();
+	return ret;
+}
+
+/**
+ * dummy_numa_init() - Fallback dummy NUMA init
+ *
+ * Used if there's no underlying NUMA architecture, NUMA initialization
+ * fails, or NUMA is disabled on the command line.
+ *
+ * Must online at least one node (node 0) and add memory blocks that cover all
+ * allowed memory. It is unlikely that this function fails.
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+static int __init dummy_numa_init(void)
+{
+	int ret;
+	struct memblock_region *mblk;
+
+	if (numa_off)
+		pr_info("NUMA disabled\n"); /* Forced off on command line. */
+	pr_info("Faking a node at [mem %#018Lx-%#018Lx]\n",
+		memblock_start_of_DRAM(), memblock_end_of_DRAM() - 1);
+
+	for_each_memblock(memory, mblk) {
+		ret = numa_add_memblk(0, mblk->base, mblk->base + mblk->size);
+		if (!ret)
+			continue;
+
+		pr_err("NUMA init failed\n");
+		return ret;
+	}
+
+	numa_off = true;
+	return 0;
+}
+
+/**
+ * riscv_numa_init() - Initialize NUMA
+ *
+ * Try each configured NUMA initialization method until one succeeds. The
+ * last fallback is dummy single node config encomapssing whole memory.
+ */
+void __init riscv_numa_init(void)
+{
+	if (!numa_off) {
+		if (!numa_init(of_numa_init))
+			return;
+	}
+
+	numa_init(dummy_numa_init);
+}
-- 
2.17.1

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