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LoongArch: Add DIRECT_MAP_PHYSMEM_END definition

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get_free_mem_region() and mhp_get_pluggable_range() bound their search
to DIRECT_MAP_PHYSMEM_END. LoongArch does not define it, so the fallback
in include/linux/mm.h applies: under CONFIG_SPARSEMEM_VMEMMAP it is
(1ULL << MAX_PHYSMEM_BITS) - 1, a compile-time constant that does not
adapt to the CPU's physical address space bits (cpu_pabits, probed from
CPUCFG1).

The vmemmap window only covers physical space below 2^(cpu_pabits+1)
(i.e. VMEMMAP_SIZE), so on CPUs with fewer physical address bits than
MAX_PHYSMEM_BITS the fallback allows get_free_mem_region() to return
a ZONE_DEVICE region outside the vmemmap window; vmemmap_populate() then
wraps the memmap range around and maps it into low memory, silently
corrupting the page tables. The same search also picked the top-of-
address-space region that crashed memmap_init_zone_device() with amdkfd
on Loongson-3C6000 in 6.16 [1]; the commit 2969b42c8f ("LoongArch/mm:
align vmemmap to maximal folio size") keeps that region in bounds on
current Loongson-3C6000 configs, but CPUs with smaller cpu_pabits (e.g.
the Loongson-2K series) are still affected.

Define DIRECT_MAP_PHYSMEM_END as the vmemmap-covered physical range,
(1ULL << (cpu_pabits + 1)) - 1, capped at (1ULL << MAX_PHYSMEM_BITS) - 1
under CONFIG_SPARSEMEM, similar to the commit f3336b48cf ("riscv: mm:
Define DIRECT_MAP_PHYSMEM_END").

[1] https://lore.kernel.org/amd-gfx/20250814032153.227285-1-jeffbai@aosc.io/

Cc: stable@vger.kernel.org # v6.13+
Signed-off-by: Han Gao <gaohan@iscas.ac.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
This commit is contained in:
Han Gao 2026-08-17 22:07:05 +08:00 committed by Huacai Chen
parent 2a2367d46d
commit 2677f97a67
1 changed files with 7 additions and 0 deletions
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7
arch/loongarch/include/asm/pgtable.h
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@ -125,6 +125,13 @@ struct vm_area_struct;
#endif
/* Needed to limit get_free_mem_region() */
#ifndef CONFIG_SPARSEMEM
#define DIRECT_MAP_PHYSMEM_END ((1ULL << (cpu_pabits + 1)) - 1)
#else
#define DIRECT_MAP_PHYSMEM_END min((1ULL << (cpu_pabits + 1)) - 1, (1ULL << MAX_PHYSMEM_BITS) - 1)
#endif
#define ptep_get(ptep) READ_ONCE(*(ptep))
#define pmdp_get(pmdp) READ_ONCE(*(pmdp))