Hi, On Sat, Jan 03, 2026 at 12:33:29AM +0100, Klara Modin wrote: > On 2026-01-02 08:59:58 +0200, Mike Rapoport wrote: > > From: "Mike Rapoport (Microsoft)" <[email protected]> > > > > To initialize node, zone and memory map data structures every architecture > > calls free_area_init() during setup_arch() and passes it an array of zone > > limits. > > > > Beside code duplication it creates "interesting" ordering cases between > > allocation and initialization of hugetlb and the memory map. Some > > architectures allocate hugetlb pages very early in setup_arch() in certain > > cases, some only create hugetlb CMA areas in setup_arch() and sometimes > > hugetlb allocations happen mm_core_init(). > > > > With arch_zone_limits_init() helper available now on all architectures it > > is no longer necessary to call free_area_init() from architecture setup > > code. Rather core MM initialization can call arch_zone_limits_init() in a > > single place. > > > > This allows to unify ordering of hugetlb vs memory map allocation and > > initialization. > > > > Remove the call to free_area_init() from architecture specific code and > > place it in a new mm_core_init_early() function that is called immediately > > after setup_arch(). > > > > After this refactoring it is possible to consolidate hugetlb allocations > > and eliminate differences in ordering of hugetlb and memory map > > initialization among different architectures. > > > > As the first step of this consolidation move hugetlb_bootmem_alloc() to > > mm_core_early_init(). > > > > Signed-off-by: Mike Rapoport (Microsoft) <[email protected]> > > This breaks boot on my Raspberry Pi 1. The reason seems to be the use of > page_folio() when initializing the dynamically allocated zero page in > arm, which doesn't work when free_area_init() hasn't been called yet.
I believe the reason is rather the use of virt_to_phys() that now happens before the memory map is ready. > The following oopses are generated: > > 8<--- cut here --- > Unable to handle kernel paging request at virtual address 003dfb44 when read > [003dfb44] *pgd=00000000 > Internal error: Oops: 5 [#1] ARM > CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted > 6.19.0-rc3-03898-g7975b0084358 #451 NONE > Hardware name: BCM2835 > PC is at paging_init (include/linux/page-flags.h:284 (discriminator 2) > arch/arm/mm/mmu.c:1790 (discriminator 2)) > LR is at paging_init (arch/arm/mm/mmu.c:1789 (discriminator 1)) ... > 8<--- cut here --- > > and the second one repeats for some time afterwards. > > I experimented a little by allocating the zero page statically as many > other arches do which fixes the issue as it does not need to be > initialized at this point anymore, though I have no idea if that's > appropriate. Do you mean putting the zero in the BSS like, e.g. arm64? I don't see a reason why this shouldn't work. I also have a patch with some minor changes that still keeps empty_zero_page allocated, but avoids virt_to_page() and folio_page() dance. Can you please test it in your setup? >From 8a213c13211106d592fbe96b68ee29879ed739f8 Mon Sep 17 00:00:00 2001 From: "Mike Rapoport (Microsoft)" <[email protected]> Date: Sat, 3 Jan 2026 20:40:09 +0200 Subject: [PATCH] arm: make initialization of zero page independent of the memory map Unlike most architectures, arm keeps a struct page pointer to the empty_zero_page and to initialize it requires conversion of a virtual address to page which makes it necessary to have memory map initialized before creating the empty_zero_page. Make empty_zero_page a void * to decouple it's initialization from the initialization of the memory map. Signed-off-by: Mike Rapoport (Microsoft) <[email protected]> --- arch/arm/include/asm/pgtable.h | 4 ++-- arch/arm/mm/mmu.c | 10 +++------- arch/arm/mm/nommu.c | 10 +++------- 3 files changed, 8 insertions(+), 16 deletions(-) diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h index 86378eec7757..08bbd2aed6c9 100644 --- a/arch/arm/include/asm/pgtable.h +++ b/arch/arm/include/asm/pgtable.h @@ -15,8 +15,8 @@ * ZERO_PAGE is a global shared page that is always zero: used * for zero-mapped memory areas etc.. */ -extern struct page *empty_zero_page; -#define ZERO_PAGE(vaddr) (empty_zero_page) +extern void *empty_zero_page; +#define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page)) #endif #include <asm-generic/pgtable-nopud.h> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c index 8bac96e205ac..867258f1ae09 100644 --- a/arch/arm/mm/mmu.c +++ b/arch/arm/mm/mmu.c @@ -45,7 +45,7 @@ extern unsigned long __atags_pointer; * empty_zero_page is a special page that is used for * zero-initialized data and COW. */ -struct page *empty_zero_page; +void *empty_zero_page; EXPORT_SYMBOL(empty_zero_page); /* @@ -1754,8 +1754,6 @@ static void __init early_fixmap_shutdown(void) */ void __init paging_init(const struct machine_desc *mdesc) { - void *zero_page; - #ifdef CONFIG_XIP_KERNEL /* Store the kernel RW RAM region start/end in these variables */ kernel_sec_start = CONFIG_PHYS_OFFSET & SECTION_MASK; @@ -1782,12 +1780,10 @@ void __init paging_init(const struct machine_desc *mdesc) top_pmd = pmd_off_k(0xffff0000); /* allocate the zero page. */ - zero_page = early_alloc(PAGE_SIZE); + empty_zero_page = early_alloc(PAGE_SIZE); + __cpuc_flush_dcache_area(empty_zero_page, PAGE_SIZE); bootmem_init(); - - empty_zero_page = virt_to_page(zero_page); - __flush_dcache_folio(NULL, page_folio(empty_zero_page)); } void __init early_mm_init(const struct machine_desc *mdesc) diff --git a/arch/arm/mm/nommu.c b/arch/arm/mm/nommu.c index d638cc87807e..f80ff5a69fbb 100644 --- a/arch/arm/mm/nommu.c +++ b/arch/arm/mm/nommu.c @@ -31,7 +31,7 @@ unsigned long vectors_base; * empty_zero_page is a special page that is used for * zero-initialized data and COW. */ -struct page *empty_zero_page; +void *empty_zero_page; EXPORT_SYMBOL(empty_zero_page); #ifdef CONFIG_ARM_MPU @@ -156,18 +156,14 @@ void __init adjust_lowmem_bounds(void) */ void __init paging_init(const struct machine_desc *mdesc) { - void *zero_page; - early_trap_init((void *)vectors_base); mpu_setup(); /* allocate the zero page. */ - zero_page = (void *)memblock_alloc_or_panic(PAGE_SIZE, PAGE_SIZE); + empty_zero_page = memblock_alloc_or_panic(PAGE_SIZE, PAGE_SIZE); + __cpuc_flush_dcache_area(empty_zero_page, PAGE_SIZE); bootmem_init(); - - empty_zero_page = virt_to_page(zero_page); - flush_dcache_page(empty_zero_page); } /* -- 2.51.0 > Regards, > Klara Modin > -- Sincerely yours, Mike.
