This patch allows the kernel to be loaded at the middle of kernel awared
physical memory. Before this patch, users must use mem= or device tree to cheat
kernel about the start address of physical memory.
This feature is useful in some special cases, for example, building a crash
dump kernel. Without it, kernel command line, atag and devicetree must be
adjusted carefully, sometimes is impossible.
Signed-off-by: Wang Nan <wangnan0 at huawei.com>
Cc: <stable at vger.kernel.org> # 3.4+
Cc: Eric Biederman <ebiederm at xmission.com>
Cc: Russell King <rmk+kernel at arm.linux.org.uk>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Geng Hui <hui.geng at huawei.com>
---
arch/arm/mm/init.c | 21 ++++++++++++++++++++-
arch/arm/mm/mmu.c | 13 +++++++++++++
mm/page_alloc.c | 7 +++++--
3 files changed, 38 insertions(+), 3 deletions(-)
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 3e8f106..4952726 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -334,9 +334,28 @@ void __init arm_memblock_init(struct meminfo *mi,
{
int i;
- for (i = 0; i < mi->nr_banks; i++)
+ for (i = 0; i < mi->nr_banks; i++) {
memblock_add(mi->bank[i].start, mi->bank[i].size);
+ /*
+ * In some special case, for example, building a crushdump
+ * kernel, we want the kernel to be loaded in the middle of
+ * physical memory. In such case, the physical memory before
+ * PHYS_OFFSET is awkward: it can't get directly mapped
+ * (because its address will be smaller than PAGE_OFFSET,
+ * disturbs user address space) also can't be mapped as
+ * HighMem. We reserve such pages here. The only way to access
+ * those pages is ioremap.
+ */
+ if (mi->bank[i].start < PHYS_OFFSET) {
+ unsigned long reserv_size = PHYS_OFFSET -
+ mi->bank[i].start;
+ if (reserv_size > mi->bank[i].size)
+ reserv_size = mi->bank[i].size;
+ memblock_reserve(mi->bank[i].start, reserv_size);
+ }
+ }
+
/* Register the kernel text, kernel data and initrd with memblock. */
#ifdef CONFIG_XIP_KERNEL
memblock_reserve(__pa(_sdata), _end - _sdata);
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 580ef2d..2a17c24 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1308,6 +1308,19 @@ static void __init map_lowmem(void)
if (start >= end)
break;
+ /*
+ * If this memblock contain memory before PAGE_OFFSET, memory
+ * before PAGE_OFFSET should't get directly mapped, see code
+ * in create_mapping(). However, memory after PAGE_OFFSET is
+ * occupyed by kernel and still need to be mapped.
+ */
+ if (__phys_to_virt(start) < PAGE_OFFSET) {
+ if (__phys_to_virt(end) > PAGE_OFFSET)
+ start = __virt_to_phys(PAGE_OFFSET);
+ else
+ break;
+ }
+
map.pfn = __phys_to_pfn(start);
map.virtual = __phys_to_virt(start);
map.length = end - start;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5248fe0..d2959e3 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4840,10 +4840,13 @@ static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat)
*/
if (pgdat == NODE_DATA(0)) {
mem_map = NODE_DATA(0)->node_mem_map;
-#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
+ /*
+ * In case of CONFIG_HAVE_MEMBLOCK_NODE_MAP or when kernel
+ * loaded at the middle of physical memory, mem_map should
+ * be adjusted.
+ */
if (page_to_pfn(mem_map) != pgdat->node_start_pfn)
mem_map -= (pgdat->node_start_pfn - ARCH_PFN_OFFSET);
-#endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
}
#endif
#endif /* CONFIG_FLAT_NODE_MEM_MAP */
--
1.8.4
