mm/memory_hotplug: introduce default phys_to_target_node() implementation

In preparation to set a fallback value for dev_dax->target_node, introduce
generic fallback helpers for phys_to_target_node()

A generic implementation based on node-data or memblock was proposed, but
as noted by Mike:

    "Here again, I would prefer to add a weak default for
     phys_to_target_node() because the "generic" implementation is not really
     generic.

     The fallback to reserved ranges is x86 specfic because on x86 most of
     the reserved areas is not in memblock.memory. AFAIK, no other
     architecture does this."

The info message in the generic memory_add_physaddr_to_nid()
implementation is fixed up to properly reflect that
memory_add_physaddr_to_nid() communicates "online" node info and
phys_to_target_node() indicates "target / to-be-onlined" node info.

[akpm@linux-foundation.org: fix CONFIG_MEMORY_HOTPLUG=n build]
  Link: https://lkml.kernel.org/r/202008252130.7YrHIyMI%25lkp@intel.com

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Jia He <justin.he@arm.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brice Goglin <Brice.Goglin@inria.fr>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@ozlabs.org>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Hulk Robot <hulkci@huawei.com>
Cc: Jason Yan <yanaijie@huawei.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Link: https://lkml.kernel.org/r/159643097768.4062302.3135192588966888630.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/mm/numa.c

@@ -917,7 +917,6 @@ int phys_to_target_node(phys_addr_t start)
 
 	return meminfo_to_nid(&numa_reserved_meminfo, start);
 }
-EXPORT_SYMBOL_GPL(phys_to_target_node);
 
 int memory_add_physaddr_to_nid(u64 start)
 {

include/linux/memory_hotplug.h

@@ -149,15 +149,6 @@ int add_pages(int nid, unsigned long start_pfn, unsigned long nr_pages,
 	      struct mhp_params *params);
 #endif /* ARCH_HAS_ADD_PAGES */
 
-#ifdef CONFIG_NUMA
-extern int memory_add_physaddr_to_nid(u64 start);
-#else
-static inline int memory_add_physaddr_to_nid(u64 start)
-{
-	return 0;
-}
-#endif
-
 #ifdef CONFIG_HAVE_ARCH_NODEDATA_EXTENSION
 /*
  * For supporting node-hotadd, we have to allocate a new pgdat.
@@ -284,6 +275,20 @@ static inline bool movable_node_is_enabled(void)
 }
 #endif /* ! CONFIG_MEMORY_HOTPLUG */
 
+#ifdef CONFIG_NUMA
+extern int memory_add_physaddr_to_nid(u64 start);
+extern int phys_to_target_node(u64 start);
+#else
+static inline int memory_add_physaddr_to_nid(u64 start)
+{
+	return 0;
+}
+static inline int phys_to_target_node(u64 start)
+{
+	return 0;
+}
+#endif
+
 #if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_DEFERRED_STRUCT_PAGE_INIT)
 /*
  * pgdat resizing functions

include/linux/numa.h

@@ -23,22 +23,11 @@
 #ifdef CONFIG_NUMA
 /* Generic implementation available */
 int numa_map_to_online_node(int node);
-
-/*
- * Optional architecture specific implementation, users need a "depends
- * on $ARCH"
- */
-int phys_to_target_node(phys_addr_t addr);
 #else
 static inline int numa_map_to_online_node(int node)
 {
 	return NUMA_NO_NODE;
 }
-
-static inline int phys_to_target_node(phys_addr_t addr)
-{
-	return NUMA_NO_NODE;
-}
 #endif
 
 #endif /* _LINUX_NUMA_H */

mm/memory_hotplug.c

@@ -353,11 +353,19 @@ int __ref __add_pages(int nid, unsigned long pfn, unsigned long nr_pages,
 #ifdef CONFIG_NUMA
 int __weak memory_add_physaddr_to_nid(u64 start)
 {
-	pr_info_once("Unknown target node for memory at 0x%llx, assuming node 0\n",
+	pr_info_once("Unknown online node for memory at 0x%llx, assuming node 0\n",
 			start);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(memory_add_physaddr_to_nid);
+
+int __weak phys_to_target_node(u64 start)
+{
+	pr_info_once("Unknown target node for memory at 0x%llx, assuming node 0\n",
+			start);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(phys_to_target_node);
 #endif
 
 /* find the smallest valid pfn in the range [start_pfn, end_pfn) */