From 66e8b438bd5c75498cfe915c4219049eaebcb869 Mon Sep 17 00:00:00 2001 From: Gioh Kim Date: Wed, 15 Nov 2017 17:33:42 -0800 Subject: mm/memblock.c: make the index explicit argument of for_each_memblock_type for_each_memblock_type macro function relies on idx variable defined in the caller context. Silent macro arguments are almost always wrong thing to do. They make code harder to read and easier to get wrong. Let's use an explicit iterator parameter for for_each_memblock_type and make the code more obious. This patch is a mere cleanup and it shouldn't introduce any functional change. Link: http://lkml.kernel.org/r/20170913133029.28911-1-gi-oh.kim@profitbricks.com Signed-off-by: Gioh Kim Acked-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/memblock.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'include/linux/memblock.h') diff --git a/include/linux/memblock.h b/include/linux/memblock.h index bae11c7e7bf3..ce0e5634c2f9 100644 --- a/include/linux/memblock.h +++ b/include/linux/memblock.h @@ -389,10 +389,10 @@ static inline unsigned long memblock_region_reserved_end_pfn(const struct memblo region < (memblock.memblock_type.regions + memblock.memblock_type.cnt); \ region++) -#define for_each_memblock_type(memblock_type, rgn) \ - for (idx = 0, rgn = &memblock_type->regions[0]; \ - idx < memblock_type->cnt; \ - idx++, rgn = &memblock_type->regions[idx]) +#define for_each_memblock_type(i, memblock_type, rgn) \ + for (i = 0, rgn = &memblock_type->regions[0]; \ + i < memblock_type->cnt; \ + i++, rgn = &memblock_type->regions[i]) #ifdef CONFIG_MEMTEST extern void early_memtest(phys_addr_t start, phys_addr_t end); -- cgit v1.2.3 From a4a3ede2132ae0863e2d43e06f9b5697c51a7a3b Mon Sep 17 00:00:00 2001 From: Pavel Tatashin Date: Wed, 15 Nov 2017 17:36:31 -0800 Subject: mm: zero reserved and unavailable struct pages Some memory is reserved but unavailable: not present in memblock.memory (because not backed by physical pages), but present in memblock.reserved. Such memory has backing struct pages, but they are not initialized by going through __init_single_page(). In some cases these struct pages are accessed even if they do not contain any data. One example is page_to_pfn() might access page->flags if this is where section information is stored (CONFIG_SPARSEMEM, SECTION_IN_PAGE_FLAGS). One example of such memory: trim_low_memory_range() unconditionally reserves from pfn 0, but e820__memblock_setup() might provide the exiting memory from pfn 1 (i.e. KVM). Since struct pages are zeroed in __init_single_page(), and not during allocation time, we must zero such struct pages explicitly. The patch involves adding a new memblock iterator: for_each_resv_unavail_range(i, p_start, p_end) Which iterates through reserved && !memory lists, and we zero struct pages explicitly by calling mm_zero_struct_page(). === Here is more detailed example of problem that this patch is addressing: Run tested on qemu with the following arguments: -enable-kvm -cpu kvm64 -m 512 -smp 2 This patch reports that there are 98 unavailable pages. They are: pfn 0 and pfns in range [159, 255]. Note, trim_low_memory_range() reserves only pfns in range [0, 15], it does not reserve [159, 255] ones. e820__memblock_setup() reports linux that the following physical ranges are available: [1 , 158] [256, 130783] Notice, that exactly unavailable pfns are missing! Now, lets check what we have in zone 0: [1, 131039] pfn 0, is not part of the zone, but pfns [1, 158], are. However, the bigger problem we have if we do not initialize these struct pages is with memory hotplug. Because, that path operates at 2M boundaries (section_nr). And checks if 2M range of pages is hot removable. It starts with first pfn from zone, rounds it down to 2M boundary (sturct pages are allocated at 2M boundaries when vmemmap is created), and checks if that section is hot removable. In this case start with pfn 1 and convert it down to pfn 0. Later pfn is converted to struct page, and some fields are checked. Now, if we do not zero struct pages, we get unpredictable results. In fact when CONFIG_VM_DEBUG is enabled, and we explicitly set all vmemmap memory to ones, the following panic is observed with kernel test without this patch applied: BUG: unable to handle kernel NULL pointer dereference at (null) IP: is_pageblock_removable_nolock+0x35/0x90 PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT ... task: ffff88001f4e2900 task.stack: ffffc90000314000 RIP: 0010:is_pageblock_removable_nolock+0x35/0x90 Call Trace: ? is_mem_section_removable+0x5a/0xd0 show_mem_removable+0x6b/0xa0 dev_attr_show+0x1b/0x50 sysfs_kf_seq_show+0xa1/0x100 kernfs_seq_show+0x22/0x30 seq_read+0x1ac/0x3a0 kernfs_fop_read+0x36/0x190 ? security_file_permission+0x90/0xb0 __vfs_read+0x16/0x30 vfs_read+0x81/0x130 SyS_read+0x44/0xa0 entry_SYSCALL_64_fastpath+0x1f/0xbd Link: http://lkml.kernel.org/r/20171013173214.27300-7-pasha.tatashin@oracle.com Signed-off-by: Pavel Tatashin Reviewed-by: Steven Sistare Reviewed-by: Daniel Jordan Reviewed-by: Bob Picco Tested-by: Bob Picco Acked-by: Michal Hocko Cc: Alexander Potapenko Cc: Andrey Ryabinin Cc: Ard Biesheuvel Cc: Catalin Marinas Cc: Christian Borntraeger Cc: David S. Miller Cc: Dmitry Vyukov Cc: Heiko Carstens Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Mark Rutland Cc: Matthew Wilcox Cc: Mel Gorman Cc: Michal Hocko Cc: Sam Ravnborg Cc: Thomas Gleixner Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/memblock.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'include/linux/memblock.h') diff --git a/include/linux/memblock.h b/include/linux/memblock.h index ce0e5634c2f9..7ed0f7782d16 100644 --- a/include/linux/memblock.h +++ b/include/linux/memblock.h @@ -237,6 +237,22 @@ unsigned long memblock_next_valid_pfn(unsigned long pfn, unsigned long max_pfn); for_each_mem_range_rev(i, &memblock.memory, &memblock.reserved, \ nid, flags, p_start, p_end, p_nid) +/** + * for_each_resv_unavail_range - iterate through reserved and unavailable memory + * @i: u64 used as loop variable + * @flags: pick from blocks based on memory attributes + * @p_start: ptr to phys_addr_t for start address of the range, can be %NULL + * @p_end: ptr to phys_addr_t for end address of the range, can be %NULL + * + * Walks over unavailable but reserved (reserved && !memory) areas of memblock. + * Available as soon as memblock is initialized. + * Note: because this memory does not belong to any physical node, flags and + * nid arguments do not make sense and thus not exported as arguments. + */ +#define for_each_resv_unavail_range(i, p_start, p_end) \ + for_each_mem_range(i, &memblock.reserved, &memblock.memory, \ + NUMA_NO_NODE, MEMBLOCK_NONE, p_start, p_end, NULL) + static inline void memblock_set_region_flags(struct memblock_region *r, unsigned long flags) { -- cgit v1.2.3