[RFC 1/3] sparse-vmemmap: let vmemmap_populate_basepages() cover the whole range

vmemmap_populate_basepages() takes two memory addresses, start and end,
and attempts to populate the page range covering it.

Due to the way this is done, namely by means of a

  for (addr = start; addr < end; addr += PAGE_SIZE) {
     ...
  }

loop, this misses the last necessary page in case of

  start % PAGE_SIZE > end % PAGE_SIZE.

On x86, Kasan's initizalization in arch/x86/mm/kasan_init_64.c (ab)uses
the arch-provided vmemmap_populate() for shadow memory population.
The start and end addresses passed aren't necessarily page aligned.

With commit 7b79d10a2d64 ("mm: convert kmalloc_section_memmap() to
populate_section_memmap()"), the x86 specific vmemmap_populate() sometimes
uses the aforementioned vmemmap_populate_basepages(). This results in
non-populated shadow memory:

  BUG: unable to handle kernel paging request at ffffed0017b4d000
  IP: memset_erms+0x9/0x10
  [...]
  Call Trace:
   ? kasan_free_pages+0x50/0x60
   free_hot_cold_page+0x382/0x9e0
   [...]
   __free_pages+0xe8/0x100
   [...]
   __free_pages_bootmem+0x1c9/0x202
   ? page_alloc_init_late+0x3a/0x3a
   ? kmemleak_free_part+0x42/0x150
   free_bootmem_late+0x5f/0x7d
   efi_free_boot_services+0x10d/0x233
   [...]

Fix this by making vmemmap_populate_basepages() round the start argument
down to a multiple of PAGE_SIZE such that the above condition can never
hold.

Signed-off-by: Nicolai Stange <redacted>
---
 mm/sparse-vmemmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 8679d4a81b98..d45bd2714a2b 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c

@@ -223,7 +223,7 @@ pgd_t * __meminit vmemmap_pgd_populate(unsigned long addr, int node)
 int __meminit vmemmap_populate_basepages(unsigned long start,
 					 unsigned long end, int node)
 {
-	unsigned long addr = start;
+	unsigned long addr = start & ~(PAGE_SIZE - 1);
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;

-- 
2.11.1

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