arch, mm: set high_memory in free_area_init()

high_memory defines upper bound on the directly mapped memory.  This bound
is defined by the beginning of ZONE_HIGHMEM when a system has high memory
and by the end of memory otherwise.

All this is known to generic memory management initialization code that
can set high_memory while initializing core mm structures.

Add a generic calculation of high_memory to free_area_init() and remove
per-architecture calculation except for the architectures that set and use
high_memory earlier than that.

Link: https://lkml.kernel.org/r/20250313135003.836600-11-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>	[x86]
Tested-by: Mark Brown <broonie@kernel.org>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Guo Ren (csky) <guoren@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Russel King <linux@armlinux.org.uk>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vineet Gupta <vgupta@kernel.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/alpha/mm/init.c

@@ -276,7 +276,6 @@ srm_paging_stop (void)
 void __init
 mem_init(void)
 {
-	high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
 	memblock_free_all();
 }
 

arch/arc/mm/init.c

@@ -150,8 +150,6 @@ void __init setup_arch_memory(void)
 	 */
 	max_zone_pfn[ZONE_HIGHMEM] = max_high_pfn;
 
-	high_memory = (void *)(min_high_pfn << PAGE_SHIFT);
-
 	arch_pfn_offset = min(min_low_pfn, min_high_pfn);
 	kmap_init();
 #endif /* CONFIG_HIGHMEM */

arch/arm64/mm/init.c

@@ -309,8 +309,6 @@ void __init arm64_memblock_init(void)
 	}
 
 	early_init_fdt_scan_reserved_mem();
-
-	high_memory = __va(memblock_end_of_DRAM() - 1) + 1;
 }
 
 void __init bootmem_init(void)

arch/csky/mm/init.c

@@ -47,7 +47,6 @@ void __init mem_init(void)
 #ifdef CONFIG_HIGHMEM
 	unsigned long tmp;
 #endif
-	high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT);
 
 	memblock_free_all();
 

arch/hexagon/mm/init.c

@@ -100,12 +100,6 @@ static void __init paging_init(void)
 	 * initial kernel segment table's physical address.
 	 */
 	init_mm.context.ptbase = __pa(init_mm.pgd);
-
-	/*
-	 * Start of high memory area.  Will probably need something more
-	 * fancy if we...  get more fancy.
-	 */
-	high_memory = (void *)((bootmem_lastpg + 1) << PAGE_SHIFT);
 }
 
 #ifndef DMA_RESERVE

arch/loongarch/kernel/numa.c

@@ -389,7 +389,6 @@ void __init paging_init(void)
 
 void __init mem_init(void)
 {
-	high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT);
 	memblock_free_all();
 }
 

arch/loongarch/mm/init.c

@@ -78,8 +78,6 @@ void __init paging_init(void)
 
 void __init mem_init(void)
 {
-	high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT);
-
 	memblock_free_all();
 }
 #endif /* !CONFIG_NUMA */

arch/microblaze/mm/init.c

@@ -120,8 +120,6 @@ void __init setup_memory(void)
 
 void __init mem_init(void)
 {
-	high_memory = (void *)__va(memory_start + lowmem_size - 1);
-
 	/* this will put all memory onto the freelists */
 	memblock_free_all();
 #ifdef CONFIG_HIGHMEM

arch/mips/mm/init.c

@@ -417,7 +417,6 @@ void __init paging_init(void)
 		max_zone_pfns[ZONE_HIGHMEM] = max_low_pfn;
 	}
 #endif
-	high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT);
 
 	free_area_init(max_zone_pfns);
 }
@@ -469,7 +468,6 @@ void __init mem_init(void)
 #else  /* CONFIG_NUMA */
 void __init mem_init(void)
 {
-	high_memory = (void *) __va(get_num_physpages() << PAGE_SHIFT);
 	setup_zero_pages();	/* This comes from node 0 */
 	memblock_free_all();
 }

arch/nios2/mm/init.c

@@ -62,12 +62,6 @@ void __init paging_init(void)
 
 void __init mem_init(void)
 {
-	unsigned long end_mem   = memory_end; /* this must not include
-						kernel stack at top */
-
-	end_mem &= PAGE_MASK;
-	high_memory = __va(end_mem);
-
 	/* this will put all memory onto the freelists */
 	memblock_free_all();
 }

arch/openrisc/mm/init.c

@@ -193,8 +193,6 @@ void __init mem_init(void)
 {
 	BUG_ON(!mem_map);
 
-	high_memory = (void *)__va(max_low_pfn * PAGE_SIZE);
-
 	/* clear the zero-page */
 	memset((void *)empty_zero_page, 0, PAGE_SIZE);
 

arch/parisc/mm/init.c

@@ -562,7 +562,6 @@ void __init mem_init(void)
 	BUILD_BUG_ON(TMPALIAS_MAP_START >= 0x80000000);
 #endif
 
-	high_memory = __va((max_pfn << PAGE_SHIFT));
 	memblock_free_all();
 
 #ifdef CONFIG_PA11

arch/riscv/mm/init.c

@@ -295,7 +295,6 @@ static void __init setup_bootmem(void)
 	phys_ram_end = memblock_end_of_DRAM();
 	min_low_pfn = PFN_UP(phys_ram_base);
 	max_low_pfn = max_pfn = PFN_DOWN(phys_ram_end);
-	high_memory = (void *)(__va(PFN_PHYS(max_low_pfn)));
 
 	dma32_phys_limit = min(4UL * SZ_1G, (unsigned long)PFN_PHYS(max_low_pfn));
 

arch/s390/mm/init.c

@@ -159,8 +159,6 @@ void __init mem_init(void)
 	cpumask_set_cpu(0, &init_mm.context.cpu_attach_mask);
 	cpumask_set_cpu(0, mm_cpumask(&init_mm));
 
-        high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
-
 	pv_init();
 	kfence_split_mapping();
 

arch/sh/mm/init.c

@@ -330,13 +330,6 @@ unsigned int mem_init_done = 0;
 
 void __init mem_init(void)
 {
-	pg_data_t *pgdat;
-
-	high_memory = NULL;
-	for_each_online_pgdat(pgdat)
-		high_memory = max_t(void *, high_memory,
-				    __va(pgdat_end_pfn(pgdat) << PAGE_SHIFT));
-
 	memblock_free_all();
 
 	/* Set this up early, so we can take care of the zero page */

arch/sparc/mm/init_32.c

@@ -275,7 +275,6 @@ void __init mem_init(void)
 
 	taint_real_pages();
 
-	high_memory = __va(max_low_pfn << PAGE_SHIFT);
 	memblock_free_all();
 
 	for (i = 0; sp_banks[i].num_bytes != 0; i++) {

arch/sparc/mm/init_64.c

@@ -2505,8 +2505,6 @@ static void __init register_page_bootmem_info(void)
 }
 void __init mem_init(void)
 {
-	high_memory = __va(last_valid_pfn << PAGE_SHIFT);
-
 	memblock_free_all();
 
 	/*

arch/um/kernel/um_arch.c

@@ -385,7 +385,6 @@ int __init linux_main(int argc, char **argv, char **envp)
 
 	high_physmem = uml_physmem + physmem_size;
 	end_iomem = high_physmem + iomem_size;
-	high_memory = (void *) end_iomem;
 
 	start_vm = VMALLOC_START;
 

arch/x86/kernel/setup.c

@@ -972,8 +972,6 @@ void __init setup_arch(char **cmdline_p)
 		max_low_pfn = e820__end_of_low_ram_pfn();
 	else
 		max_low_pfn = max_pfn;
-
-	high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
 #endif
 
 	/* Find and reserve MPTABLE area */

arch/x86/mm/init_32.c

@@ -643,9 +643,6 @@ void __init initmem_init(void)
 		highstart_pfn = max_low_pfn;
 	printk(KERN_NOTICE "%ldMB HIGHMEM available.\n",
 		pages_to_mb(highend_pfn - highstart_pfn));
-	high_memory = (void *) __va(highstart_pfn * PAGE_SIZE - 1) + 1;
-#else
-	high_memory = (void *) __va(max_low_pfn * PAGE_SIZE - 1) + 1;
 #endif
 
 	memblock_set_node(0, PHYS_ADDR_MAX, &memblock.memory, 0);

arch/x86/mm/numa_32.c

@@ -41,9 +41,6 @@ void __init initmem_init(void)
 		highstart_pfn = max_low_pfn;
 	printk(KERN_NOTICE "%ldMB HIGHMEM available.\n",
 	       pages_to_mb(highend_pfn - highstart_pfn));
-	high_memory = (void *) __va(highstart_pfn * PAGE_SIZE - 1) + 1;
-#else
-	high_memory = (void *) __va(max_low_pfn * PAGE_SIZE - 1) + 1;
 #endif
 	printk(KERN_NOTICE "%ldMB LOWMEM available.\n",
 			pages_to_mb(max_low_pfn));

arch/xtensa/mm/init.c

@@ -164,8 +164,6 @@ void __init mem_init(void)
 {
 	free_highpages();
 
-	high_memory = (void *)__va(max_low_pfn << PAGE_SHIFT);
-
 	memblock_free_all();
 }
 

mm/memory.c

@@ -113,14 +113,6 @@ static __always_inline bool vmf_orig_pte_uffd_wp(struct vm_fault *vmf)
 	return pte_marker_uffd_wp(vmf->orig_pte);
 }
 
-/*
- * A number of key systems in x86 including ioremap() rely on the assumption
- * that high_memory defines the upper bound on direct map memory, then end
- * of ZONE_NORMAL.
- */
-void *high_memory;
-EXPORT_SYMBOL(high_memory);
-
 /*
  * Randomize the address space (stacks, mmaps, brk, etc.).
  *

mm/mm_init.c

@@ -45,6 +45,13 @@ struct page *mem_map;
 EXPORT_SYMBOL(mem_map);
 #endif
 
+/*
+ * high_memory defines the upper bound on direct map memory, then end
+ * of ZONE_NORMAL.
+ */
+void *high_memory;
+EXPORT_SYMBOL(high_memory);
+
 #ifdef CONFIG_DEBUG_MEMORY_INIT
 int __meminitdata mminit_loglevel;
 
@@ -1778,6 +1785,27 @@ static bool arch_has_descending_max_zone_pfns(void)
 	return IS_ENABLED(CONFIG_ARC) && !IS_ENABLED(CONFIG_ARC_HAS_PAE40);
 }
 
+static void set_high_memory(void)
+{
+	phys_addr_t highmem = memblock_end_of_DRAM();
+
+	/*
+	 * Some architectures (e.g. ARM) set high_memory very early and
+	 * use it in arch setup code.
+	 * If an architecture already set high_memory don't overwrite it
+	 */
+	if (high_memory)
+		return;
+
+#ifdef CONFIG_HIGHMEM
+	if (arch_has_descending_max_zone_pfns() ||
+	    highmem > PFN_PHYS(arch_zone_lowest_possible_pfn[ZONE_HIGHMEM]))
+		highmem = PFN_PHYS(arch_zone_lowest_possible_pfn[ZONE_HIGHMEM]);
+#endif
+
+	high_memory = phys_to_virt(highmem - 1) + 1;
+}
+
 /**
  * free_area_init - Initialise all pg_data_t and zone data
  * @max_zone_pfn: an array of max PFNs for each zone
@@ -1900,6 +1928,8 @@ void __init free_area_init(unsigned long *max_zone_pfn)
 
 	/* disable hash distribution for systems with a single node */
 	fixup_hashdist();
+
+	set_high_memory();
 }
 
 /**

mm/nommu.c

@@ -42,8 +42,6 @@
 #include <asm/mmu_context.h>
 #include "internal.h"
 
-void *high_memory;
-EXPORT_SYMBOL(high_memory);
 unsigned long highest_memmap_pfn;
 int sysctl_nr_trim_pages = CONFIG_NOMMU_INITIAL_TRIM_EXCESS;
 int heap_stack_gap = 0;