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Catalin Marinas >> ; Will Deacon ; Andrew >> Morton ; Uladzislau Rezki >> Cc: Anshuman Khandual ; Ryan Roberts >> ; Peter Xu ; Joey Gouly >> ; Yicong Yang ; Matthew >> Wilcox (Oracle) ; linux-arm-kernel@lists.infradead.org; >> linux-kernel@vger.kernel.org; linux-mm@kvack.org >> Subject: Re: [PATCH] mm: vmalloc: use VMALLOC_EARLY_START boundary for >> early vmap area >> >> >> On 22/07/25 9:38 am, Jia He wrote: >>> When VMALLOC_START is redefined to a new boundary, most subsystems >>> continue to function correctly. However, vm_area_register_early() >>> assumes the use of the global _vmlist_ structure before vmalloc_init() >>> is invoked. This assumption can lead to issues during early boot. >>> >>> See the calltrace as follows: >>> start_kernel() >>> setup_per_cpu_areas() >>> pcpu_page_first_chunk() >>> vm_area_register_early() >>> mm_core_init() >>> vmalloc_init() >>> >>> The early vm areas will be added to vmlist at declare_kernel_vmas() >>> ->declare_vma(): >>> ffff800080010000 T _stext >>> ffff800080da0000 D __start_rodata >>> ffff800081890000 T __inittext_begin >>> ffff800081980000 D __initdata_begin >>> ffff800081ee0000 D _data >>> The starting address of the early areas is tied to the *old* >>> VMALLOC_START (i.e. 0xffff800080000000 on an arm64 N2 server). >>> >>> If VMALLOC_START is redefined, it can disrupt early VM area >>> allocation, particularly in like pcpu_page_first_chunk()- >>> vm_area_register_early(). >>> >>> To address this potential risk on arm64, introduce a new boundary, >>> VMALLOC_EARLY_START, to avoid boot issues when VMALLOC_START is >>> occasionaly redefined. >> Sorry but I am unable to understand the point of the patch. If a particular >> value of VMALLOC_START causes a problem because the vma declarations of >> the kernel are tied to that value, surely we should be reasoning about what >> was wrong about the new value, and not circumventing the actual problem by >> introducing VMALLOC_EARLY_START? >> >> Also by your patch description I don't think you have run into a reproducible >> boot issue, so this patch is basically adding dead code because both macros >> are defined to MODULES_END? >> > Please try this *debugging* purpose patch which can trigger the boot panic > more easily(I can always reproduce the boot panic on an ARM64 server): > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 192d86e1cc76..2be8db8d0205 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -20,7 +20,8 @@ > * VMALLOC_START: beginning of the kernel vmalloc space > * VMALLOC_END: extends to the available space below vmemmap > */ > -#define VMALLOC_START (MODULES_END) > +//#define VMALLOC_START (MODULES_END) > +#define VMALLOC_START ((MODULES_END & PGDIR_MASK) + PGDIR_SIZE) > #if VA_BITS == VA_BITS_MIN > #define VMALLOC_END (VMEMMAP_START - SZ_8M) > #else > diff --git a/mm/percpu.c b/mm/percpu.c > index b35494c8ede2..53d187172b5e 100644 > --- a/mm/percpu.c > +++ b/mm/percpu.c > @@ -3051,7 +3051,7 @@ int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size, > max_distance += ai->unit_size * ai->groups[highest_group].nr_units; > > /* warn if maximum distance is further than 75% of vmalloc space */ > - if (max_distance > VMALLOC_TOTAL * 3 / 4) { > + if (1 || max_distance > VMALLOC_TOTAL * 3 / 4) { This will always return true - which leads to returning -EINVAL and then panicking in setup_per_cpu_areas(). Probably you made this change by mistake and are trying to say that the redefinition above panics? > pr_warn("max_distance=0x%lx too large for vmalloc space 0x%lx\n", > max_distance, VMALLOC_TOTAL); > #ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK > > > --- > Cheers, > Justin He(Jia He) > >