[PATCH Resend] ARM: kdump: makes second kernel use strict pfn_valid

[Wang Nan]

When SPARSEMEM and CRASH_DUMP both selected, simple pfn_valid prevents
the second kernel ioremap first kernel's memory if the address falls
into second kernel section. This limitation requires the second kernel
occupies a full section, and elfcorehdr must resides in another section.

This patch makes crash dump kernel use strict pfn_valid, removes such
limitation.

For example:

  For a platform with SECTION_SIZE_BITS == 28 (256MiB) and
  crashkernel=128M at 0x28000000 in kernel cmdline, the second
  kernel is loaded at 0x28000000. Kexec puts elfcorehdr at
  0x2ff00000, and passes 'elfcorehdr=0x2ff00000 mem=130048K' to
  second kernel. When second kernel start, it tries to use
  ioremap to retrive its elfcorehrd. In this case, elfcodehdr is at the
  same section of the second kernel, pfn_valid will recongnize
  the page as valid, so ioremap will refuse to map it.

Signed-off-by: Wang Nan <wangnan0 at huawei.com>
Cc: Geng Hui <hui.geng at huawei.com>
---

I have sent this patch once, but get no response. Resend with commit
message update.

---
 arch/arm/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index db3c541..795b1d4 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1800,7 +1800,7 @@ config ARCH_SELECT_MEMORY_MODEL
 	def_bool ARCH_SPARSEMEM_ENABLE
 
 config HAVE_ARCH_PFN_VALID
-	def_bool ARCH_HAS_HOLES_MEMORYMODEL || !SPARSEMEM
+	def_bool ARCH_HAS_HOLES_MEMORYMODEL || !SPARSEMEM || CRASH_DUMP
 
 config HIGHMEM
 	bool "High Memory Support"
-- 
1.8.4