Commit 484b90c4 authored Sep 03, 2005 by Vivek Goyal Committed by Linus Torvalds Sep 05, 2005

[PATCH] kdump: Save parameter segment in protected mode (x86)

o With introduction of kexec as boot-loader, the assumption that parameter
segment will always be loaded at lower address than kernel and will be
addressable by early bootup page tables is no longer valid. In kexec on
panic case parameter segment might well be loaded beyond kernel image and
might not be addressable by early boot page tables.
o This case might hit in the scenario where user has reserved a chunk of
memory for second kernel, for example 16MB to 64MB, and has also built
second kernel for physical memory location 16MB. In this case kexec has no
choice but to load the parameter segment at a higher address than new kernel
image at safe location where new kernel does not stomp it.
o Though problem should automatically go away once relocatable kernel for i386
is in place and kexec can determine the location of new kernel at run time
and load parameter segment at lower address than kernel image. But till then
this patch can go in (assuming it does not break something else).
o This patch moves up the boot parameter saving code. Now boot parameters
are copied out in protected mode before page tables are initialized. This
will ensure that parameter segment is always addressable irrespective of
its physical location.

Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent 5fd75ebb

arch/i386/kernel/head.S

+26 −22

Original line number	Diff line number	Diff line
		@@ -77,6 +77,32 @@ ENTRY(startup_32)
		subl %edi,%ecx
		shrl $2,%ecx
		rep ; stosl
		/*
		* Copy bootup parameters out of the way.
		* Note: %esi still has the pointer to the real-mode data.
		* With the kexec as boot loader, parameter segment might be loaded beyond
		* kernel image and might not even be addressable by early boot page tables.
		* (kexec on panic case). Hence copy out the parameters before initializing
		* page tables.
		*/
		movl $(boot_params - __PAGE_OFFSET),%edi
		movl $(PARAM_SIZE/4),%ecx
		cld
		rep
		movsl
		movl boot_params - __PAGE_OFFSET + NEW_CL_POINTER,%esi
		andl %esi,%esi
		jnz 2f # New command line protocol
		cmpw $(OLD_CL_MAGIC),OLD_CL_MAGIC_ADDR
		jne 1f
		movzwl OLD_CL_OFFSET,%esi
		addl $(OLD_CL_BASE_ADDR),%esi
		2:
		movl $(saved_command_line - __PAGE_OFFSET),%edi
		movl $(COMMAND_LINE_SIZE/4),%ecx
		rep
		movsl
		1:

		/*
		* Initialize page tables. This creates a PDE and a set of page
		@@ -214,28 +240,6 @@ ENTRY(startup_32_smp)
		*/
		call setup_idt

		/*
		* Copy bootup parameters out of the way.
		* Note: %esi still has the pointer to the real-mode data.
		*/
		movl $boot_params,%edi
		movl $(PARAM_SIZE/4),%ecx
		cld
		rep
		movsl
		movl boot_params+NEW_CL_POINTER,%esi
		andl %esi,%esi
		jnz 2f # New command line protocol
		cmpw $(OLD_CL_MAGIC),OLD_CL_MAGIC_ADDR
		jne 1f
		movzwl OLD_CL_OFFSET,%esi
		addl $(OLD_CL_BASE_ADDR),%esi
		2:
		movl $saved_command_line,%edi
		movl $(COMMAND_LINE_SIZE/4),%ecx
		rep
		movsl
		1:
		checkCPUtype:

		movl $-1,X86_CPUID # -1 for no CPUID initially