RE: [PATCH] [RESEND] arm: limit memblock base address for early_pte_alloc

Kim, Jong-Sung
2012-06-08T13:58:54Z

> From: Minchan Kim [mailto:minchan@kernel.org]
> Sent: Tuesday, June 05, 2012 4:12 PM
>
> If we do arm_memblock_steal with a page which is not aligned with section
> size, panic can happen during boot by page fault in map_lowmem.
>
> Detail:
>
> 1) mdesc->reserve can steal a page which is allocated at 0x1ffff000 by
> memblock
> which prefers tail pages of regions.
> 2) map_lowmem maps 0x00000000 - 0x1fe00000
> 3) map_lowmem try to map 0x1fe00000 but it's not aligned by section due to
1.
> 4) calling alloc_init_pte allocates a new page for new pte by
memblock_alloc
> 5) allocated memory for pte is 0x1fffe000 -> it's not mapped yet.
> 6) memset(ptr, 0, sz) in early_alloc_aligned got PANICed!

May I suggest another simple approach? The first continuous couples of
sections are always safely section-mapped inside alloc_init_section funtion.
So, by limiting memblock_alloc to the end of the first continuous couples of
sections at the start of map_lowmem, map_lowmem can safely memblock_alloc &
memset even if we have one or more section-unaligned memory regions. The
limit can be extended back to arm_lowmem_limit after the map_lowmem is done.

diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index e5dad60..edf1e2d 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1094,6 +1094,11 @@ static void __init kmap_init(void)
static void __init map_lowmem(void)
{
struct memblock_region *reg;
+ phys_addr_t pmd_map_end;
+
+ pmd_map_end = (memblock.memory.regions[0].base +
+ memblock.memory.regions[0].size) & PMD_MASK;
+ memblock_set_current_limit(pmd_map_end);

/* Map all the lowmem memory banks. */
for_each_memblock(memory, reg) {
@@ -1113,6 +1118,8 @@ static void __init map_lowmem(void)

create_mapping(&map);
}
+
+ memblock_set_current_limit(arm_lowmem_limit);
}

/*
@@ -1123,8 +1130,6 @@ void __init paging_init(struct machine_desc *mdesc)
{
void *zero_page;

- memblock_set_current_limit(arm_lowmem_limit);
-
build_mem_type_table();
prepare_page_table();
map_lowmem();