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arch, mm: set high_memory in free_area_init()
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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>
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Mike Rapoport (Microsoft) authored and Andrew Morton committed Mar 18, 2025
1 parent 8268af3 commit e120d1b
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Showing 25 changed files with 30 additions and 62 deletions.
1 change: 0 additions & 1 deletion arch/alpha/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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();
}

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2 changes: 0 additions & 2 deletions arch/arc/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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 */
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2 changes: 0 additions & 2 deletions arch/arm64/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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)
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1 change: 0 additions & 1 deletion arch/csky/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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();

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6 changes: 0 additions & 6 deletions arch/hexagon/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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
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1 change: 0 additions & 1 deletion arch/loongarch/kernel/numa.c
Original file line number Diff line number Diff line change
Expand Up @@ -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();
}

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2 changes: 0 additions & 2 deletions arch/loongarch/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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 */
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2 changes: 0 additions & 2 deletions arch/microblaze/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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
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2 changes: 0 additions & 2 deletions arch/mips/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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);
}
Expand Down Expand Up @@ -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();
}
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6 changes: 0 additions & 6 deletions arch/nios2/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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();
}
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2 changes: 0 additions & 2 deletions arch/openrisc/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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);

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1 change: 0 additions & 1 deletion arch/parisc/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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
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1 change: 0 additions & 1 deletion arch/riscv/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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));

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2 changes: 0 additions & 2 deletions arch/s390/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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();

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7 changes: 0 additions & 7 deletions arch/sh/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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 */
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1 change: 0 additions & 1 deletion arch/sparc/mm/init_32.c
Original file line number Diff line number Diff line change
Expand Up @@ -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++) {
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2 changes: 0 additions & 2 deletions arch/sparc/mm/init_64.c
Original file line number Diff line number Diff line change
Expand Up @@ -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();

/*
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1 change: 0 additions & 1 deletion arch/um/kernel/um_arch.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;

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2 changes: 0 additions & 2 deletions arch/x86/kernel/setup.c
Original file line number Diff line number Diff line change
Expand Up @@ -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 */
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3 changes: 0 additions & 3 deletions arch/x86/mm/init_32.c
Original file line number Diff line number Diff line change
Expand Up @@ -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);
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3 changes: 0 additions & 3 deletions arch/x86/mm/numa_32.c
Original file line number Diff line number Diff line change
Expand Up @@ -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));
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2 changes: 0 additions & 2 deletions arch/xtensa/mm/init.c
Original file line number Diff line number Diff line change
Expand Up @@ -164,8 +164,6 @@ void __init mem_init(void)
{
free_highpages();

high_memory = (void *)__va(max_low_pfn << PAGE_SHIFT);

memblock_free_all();
}

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8 changes: 0 additions & 8 deletions mm/memory.c
Original file line number Diff line number Diff line change
Expand Up @@ -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.).
*
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30 changes: 30 additions & 0 deletions mm/mm_init.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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();
}

/**
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2 changes: 0 additions & 2 deletions mm/nommu.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
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