The libnvdimm sub-system has suffered a series of hacks and broken workarounds for the memory-hotplug implementation's awkward section-aligned (128MB) granularity. For example the following backtrace is emitted when attempting arch_add_memory() with physical address ranges that intersect 'System RAM' (RAM) with 'Persistent Memory' (PMEM) within a given section: WARNING: CPU: 0 PID: 558 at kernel/memremap.c:300 devm_memremap_pages+0x3b5/0x4c0 devm_memremap_pages attempted on mixed region [mem 0x200000000-0x2fbffffff flags 0x200] [..] Call Trace: dump_stack+0x86/0xc3 __warn+0xcb/0xf0 warn_slowpath_fmt+0x5f/0x80 devm_memremap_pages+0x3b5/0x4c0 __wrap_devm_memremap_pages+0x58/0x70 [nfit_test_iomap] pmem_attach_disk+0x19a/0x440 [nd_pmem] Recently it was discovered that the problem goes beyond RAM vs PMEM collisions as some platform produce PMEM vs PMEM collisions within a given section. The libnvdimm workaround for that case revealed that the libnvdimm section-alignment-padding implementation has been broken for a long while. A fix for that long-standing breakage introduces as many problems as it solves as it would require a backward-incompatible change to the namespace metadata interpretation. Instead of that dubious route [1], address the root problem in the memory-hotplug implementation. [1]: https://lore.kernel.org/r/155000671719.348031.2347363160141119237.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> --- mm/sparse.c | 223 ++++++++++++++++++++++++++++++++++++++++------------------- 1 file changed, 150 insertions(+), 73 deletions(-) diff --git a/mm/sparse.c b/mm/sparse.c index 198371e5fc87..419a3620af6e 100644 --- a/mm/sparse.c +++ b/mm/sparse.c @@ -83,8 +83,15 @@ static int __meminit sparse_index_init(unsigned long section_nr, int nid) unsigned long root = SECTION_NR_TO_ROOT(section_nr); struct mem_section *section; + /* + * An existing section is possible in the sub-section hotplug + * case. First hot-add instantiates, follow-on hot-add reuses + * the existing section. + * + * The mem_hotplug_lock resolves the apparent race below. + */ if (mem_section[root]) - return -EEXIST; + return 0; section = sparse_index_alloc(nid); if (!section) @@ -338,6 +345,15 @@ static void __meminit sparse_init_one_section(struct mem_section *ms, unsigned long pnum, struct page *mem_map, struct mem_section_usage *usage) { + /* + * Given that SPARSEMEM_VMEMMAP=y supports sub-section hotplug, + * ->section_mem_map can not be guaranteed to point to a full + * section's worth of memory. The field is only valid / used + * in the SPARSEMEM_VMEMMAP=n case. + */ + if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP)) + mem_map = NULL; + ms->section_mem_map &= ~SECTION_MAP_MASK; ms->section_mem_map |= sparse_encode_mem_map(mem_map, pnum) | SECTION_HAS_MEM_MAP; @@ -743,10 +759,130 @@ static void free_map_bootmem(struct page *memmap) #endif /* CONFIG_MEMORY_HOTREMOVE */ #endif /* CONFIG_SPARSEMEM_VMEMMAP */ +#ifndef CONFIG_MEMORY_HOTREMOVE +static void free_map_bootmem(struct page *memmap) +{ +} +#endif + +static bool is_early_section(struct mem_section *ms) +{ + struct page *usage_page; + + usage_page = virt_to_page(ms->usage); + if (PageSlab(usage_page) || PageCompound(usage_page)) + return false; + else + return true; +} + +static void section_deactivate(unsigned long pfn, unsigned long nr_pages, + int nid, struct vmem_altmap *altmap) +{ + unsigned long mask = section_active_mask(pfn, nr_pages); + struct mem_section *ms = __pfn_to_section(pfn); + bool early_section = is_early_section(ms); + struct page *memmap = NULL; + + if (WARN(!ms->usage || (ms->usage->map_active & mask) != mask, + "section already deactivated: active: %#lx mask: %#lx\n", + ms->usage ? ms->usage->map_active : 0, mask)) + return; + + if (WARN(!IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) + && nr_pages < PAGES_PER_SECTION, + "partial memory section removal not supported\n")) + return; + + /* + * There are 3 cases to handle across two configurations + * (SPARSEMEM_VMEMMAP={y,n}): + * + * 1/ deactivation of a partial hot-added section (only possible + * in the SPARSEMEM_VMEMMAP=y case). + * a/ section was present at memory init + * b/ section was hot-added post memory init + * 2/ deactivation of a complete hot-added section + * 3/ deactivation of a complete section from memory init + * + * For 1/, when map_active does not go to zero we will not be + * freeing the usage map, but still need to free the vmemmap + * range. + * + * For 2/ and 3/ the SPARSEMEM_VMEMMAP={y,n} cases are unified + */ + ms->usage->map_active ^= mask; + if (ms->usage->map_active == 0) { + unsigned long section_nr = pfn_to_section_nr(pfn); + + if (!early_section) { + kfree(ms->usage); + ms->usage = NULL; + } + memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr); + ms->section_mem_map = sparse_encode_mem_map(NULL, section_nr); + } + + if (early_section && memmap) + free_map_bootmem(memmap); + else + depopulate_section_memmap(pfn, nr_pages, altmap); +} + +static struct page * __meminit section_activate(int nid, unsigned long pfn, + unsigned long nr_pages, struct vmem_altmap *altmap) +{ + unsigned long mask = section_active_mask(pfn, nr_pages); + struct mem_section *ms = __pfn_to_section(pfn); + struct mem_section_usage *usage = NULL; + struct page *memmap; + int rc = 0; + + if (!ms->usage) { + usage = kzalloc(mem_section_usage_size(), GFP_KERNEL); + if (!usage) + return ERR_PTR(-ENOMEM); + ms->usage = usage; + } + + if (!mask) + rc = -EINVAL; + else if (mask & ms->usage->map_active) + rc = -EEXIST; + else + ms->usage->map_active |= mask; + + if (rc) { + if (usage) + ms->usage = NULL; + kfree(usage); + return ERR_PTR(rc); + } + + /* + * The early init code does not consider partially populated + * initial sections, it simply assumes that memory will never be + * referenced. If we hot-add memory into such a section then we + * do not need to populate the memmap and can simply reuse what + * is already there. + */ + if (nr_pages < PAGES_PER_SECTION && is_early_section(ms)) + return pfn_to_page(pfn); + + memmap = populate_section_memmap(pfn, nr_pages, nid, altmap); + if (!memmap) { + section_deactivate(pfn, nr_pages, nid, altmap); + return ERR_PTR(-ENOMEM); + } + + return memmap; +} + /** - * sparse_add_one_section - add a memory section + * sparse_add_section - add a memory section, or populate an existing one * @nid: The node to add section on * @start_pfn: start pfn of the memory range + * @nr_pages: number of pfns to add in the section * @altmap: device page map * * This is only intended for hotplug. @@ -760,49 +896,31 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn, unsigned long nr_pages, struct vmem_altmap *altmap) { unsigned long section_nr = pfn_to_section_nr(start_pfn); - struct mem_section_usage *usage; struct mem_section *ms; struct page *memmap; int ret; - /* - * no locking for this, because it does its own - * plus, it does a kmalloc - */ ret = sparse_index_init(section_nr, nid); if (ret < 0 && ret != -EEXIST) return ret; - ret = 0; - memmap = populate_section_memmap(start_pfn, PAGES_PER_SECTION, nid, - altmap); - if (!memmap) - return -ENOMEM; - usage = kzalloc(mem_section_usage_size(), GFP_KERNEL); - if (!usage) { - depopulate_section_memmap(start_pfn, PAGES_PER_SECTION, altmap); - return -ENOMEM; - } - ms = __pfn_to_section(start_pfn); - if (ms->section_mem_map & SECTION_MARKED_PRESENT) { - ret = -EEXIST; - goto out; - } + memmap = section_activate(nid, start_pfn, nr_pages, altmap); + if (IS_ERR(memmap)) + return PTR_ERR(memmap); + ret = 0; /* * Poison uninitialized struct pages in order to catch invalid flags * combinations. */ - page_init_poison(memmap, sizeof(struct page) * PAGES_PER_SECTION); + page_init_poison(pfn_to_page(start_pfn), sizeof(struct page) * nr_pages); + ms = __pfn_to_section(start_pfn); section_mark_present(ms); - sparse_init_one_section(ms, section_nr, memmap, usage); + sparse_init_one_section(ms, section_nr, memmap, ms->usage); -out: - if (ret < 0) { - kfree(usage); - depopulate_section_memmap(start_pfn, PAGES_PER_SECTION, altmap); - } + if (ret < 0) + section_deactivate(start_pfn, nr_pages, nid, altmap); return ret; } @@ -837,54 +955,13 @@ static inline void clear_hwpoisoned_pages(struct page *memmap, int nr_pages) } #endif -static void free_section_usage(struct page *memmap, - struct mem_section_usage *usage, unsigned long pfn, - unsigned long nr_pages, struct vmem_altmap *altmap) -{ - struct page *usage_page; - - if (!usage) - return; - - usage_page = virt_to_page(usage); - /* - * Check to see if allocation came from hot-plug-add - */ - if (PageSlab(usage_page) || PageCompound(usage_page)) { - kfree(usage); - if (memmap) - depopulate_section_memmap(pfn, nr_pages, altmap); - return; - } - - /* - * The usemap came from bootmem. This is packed with other usemaps - * on the section which has pgdat at boot time. Just keep it as is now. - */ - - if (memmap) - free_map_bootmem(memmap); -} - void sparse_remove_section(struct zone *zone, struct mem_section *ms, unsigned long pfn, unsigned long nr_pages, unsigned long map_offset, struct vmem_altmap *altmap) { - struct page *memmap = NULL; - struct mem_section_usage *usage = NULL; - - if (ms->section_mem_map) { - usage = ms->usage; - memmap = sparse_decode_mem_map(ms->section_mem_map, - __section_nr(ms)); - ms->section_mem_map = 0; - ms->usage = NULL; - } - - clear_hwpoisoned_pages(memmap + map_offset, - PAGES_PER_SECTION - map_offset); - free_section_usage(memmap, usage, section_nr_to_pfn(__section_nr(ms)), - PAGES_PER_SECTION, altmap); + clear_hwpoisoned_pages(pfn_to_page(pfn) + map_offset, + nr_pages - map_offset); + section_deactivate(pfn, nr_pages, zone_to_nid(zone), altmap); } #endif /* CONFIG_MEMORY_HOTREMOVE */ #endif /* CONFIG_MEMORY_HOTPLUG */
