When sizeof(struct page) is not a power of 2, sections do not span a PMD anymore and so when populating them some parts of the PMD will remain unused. Because of this, PMDs will be left behind when depopulating sections since remove_pmd_table() thinks that those unused parts are still in use.
Fix this by marking the unused parts with PAGE_UNUSED, so memchr_inv() will do the right thing and will let us free the PMD when the last user of it is gone. This patch is based on a similar patch by David Hildenbrand: https://lore.kernel.org/linux-mm/20200722094558.9828-9-da...@redhat.com/ Signed-off-by: Oscar Salvador <osalva...@suse.de> Reviewed-by: David Hildenbrand <da...@redhat.com> Acked-by: Dave Hansen <dave.han...@linux.intel.com> --- arch/x86/mm/init_64.c | 65 +++++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 53 insertions(+), 12 deletions(-) diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c index 9ecb3c488ac8..d93b36856ed3 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -826,6 +826,51 @@ void __init paging_init(void) zone_sizes_init(); } +#ifdef CONFIG_SPARSEMEM_VMEMMAP +#define PAGE_UNUSED 0xFD + +/* Returns true if the PMD is completely unused and thus it can be freed */ +static bool __meminit vmemmap_pmd_is_unused(unsigned long addr, unsigned long end) +{ + unsigned long start = ALIGN_DOWN(addr, PMD_SIZE); + + memset((void *)addr, PAGE_UNUSED, end - addr); + + return !memchr_inv((void *)start, PAGE_UNUSED, PMD_SIZE); +} + +static void __meminit vmemmap_use_sub_pmd(unsigned long start) +{ + /* + * As we expect to add in the same granularity as we remove, it's + * sufficient to mark only some piece used to block the memmap page from + * getting removed when removing some other adjacent memmap (just in + * case the first memmap never gets initialized e.g., because the memory + * block never gets onlined). + */ + memset((void *)start, 0, sizeof(struct page)); +} + +static void __meminit vmemmap_use_new_sub_pmd(unsigned long start, unsigned long end) +{ + /* + * Could be our memmap page is filled with PAGE_UNUSED already from a + * previous remove. Make sure to reset it. + */ + vmemmap_use_sub_pmd(start); + + /* + * Mark with PAGE_UNUSED the unused parts of the new memmap range + */ + if (!IS_ALIGNED(start, PMD_SIZE)) + memset((void *)start, PAGE_UNUSED, + start - ALIGN_DOWN(start, PMD_SIZE)); + if (!IS_ALIGNED(end, PMD_SIZE)) + memset((void *)end, PAGE_UNUSED, + ALIGN(end, PMD_SIZE) - end); +} +#endif + /* * Memory hotplug specific functions */ @@ -871,8 +916,6 @@ int arch_add_memory(int nid, u64 start, u64 size, return add_pages(nid, start_pfn, nr_pages, params); } -#define PAGE_INUSE 0xFD - static void __meminit free_pagetable(struct page *page, int order) { unsigned long magic; @@ -1006,7 +1049,6 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end, unsigned long next, pages = 0; pte_t *pte_base; pmd_t *pmd; - void *page_addr; pmd = pmd_start + pmd_index(addr); for (; addr < end; addr = next, pmd++) { @@ -1026,20 +1068,13 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end, pmd_clear(pmd); spin_unlock(&init_mm.page_table_lock); pages++; - } else { - /* If here, we are freeing vmemmap pages. */ - memset((void *)addr, PAGE_INUSE, next - addr); - - page_addr = page_address(pmd_page(*pmd)); - if (!memchr_inv(page_addr, PAGE_INUSE, - PMD_SIZE)) { + } else if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) && + vmemmap_pmd_is_unused(addr, next)) { free_hugepage_table(pmd_page(*pmd), altmap); - spin_lock(&init_mm.page_table_lock); pmd_clear(pmd); spin_unlock(&init_mm.page_table_lock); - } } continue; @@ -1492,11 +1527,17 @@ static int __meminit vmemmap_populate_hugepages(unsigned long start, addr_end = addr + PMD_SIZE; p_end = p + PMD_SIZE; + + if (!IS_ALIGNED(addr, PMD_SIZE) || + !IS_ALIGNED(next, PMD_SIZE)) + vmemmap_use_new_sub_pmd(addr, next); + continue; } else if (altmap) return -ENOMEM; /* no fallback */ } else if (pmd_large(*pmd)) { vmemmap_verify((pte_t *)pmd, node, addr, next); + vmemmap_use_sub_pmd(addr); continue; } if (vmemmap_populate_basepages(addr, next, node, NULL)) -- 2.16.3
