linux-kernel - [PATCH 3/3] ARM: allow kernel to be loaded in middle of phymem

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Message-ID: <1390389916-8711-4-git-send-email-wangnan0@huawei.com>
Date:	Wed, 22 Jan 2014 19:25:16 +0800
From:	Wang Nan <wangnan0@...wei.com>
To:	<kexec@...ts.infradead.org>
CC:	Eric Biederman <ebiederm@...ssion.com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Geng Hui <hui.geng@...wei.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	Wang Nan <wangnan0@...wei.com>, <stable@...r.kernel.org>
Subject: [PATCH 3/3] ARM: allow kernel to be loaded in middle of phymem

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@...wei.com>
Cc: <stable@...r.kernel.org> # 3.4+
Cc: Eric Biederman <ebiederm@...ssion.com>
Cc: Russell King <rmk+kernel@....linux.org.uk>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Geng Hui <hui.geng@...wei.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

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