[PATCH 3/3] powerpc/ppc64/kdump: better flag for running relocatable

[PATCH 3/3] powerpc/ppc64/kdump: better flag for running relocatable

[Milton Miller]

The __kdump_flag ABI is overly constraining for future development.  

As of 2.6.27, the kernel entry point has 4 constraints:  Offset 0 is
the starting point for the master (boot) cpu (entered with r3 pointing
to the device tree structure), offset 0x60 is code for the slave cpus
(entered with r3 set to their device tree physical id), offset 0x20 is
used by the iseries hypervisor, and secondary cpus must be well behaved
when the first 256 bytes are copied to address 0.

Placing the __kdump_flag at 0x18 is bad because:

- It was taking the last 8 bytes before the iseries hypervisor data.  
- It was 8 bytes for a boolean flag
- It had no way of identifying that the flag was present
- It does leave any room for the master to add any additional code
  before branching, which hurts debug.
- It will be unnecessarily hard for 32 bit code to be common (8 bytes)

Now that we have eliminated the use of __kdump_flag in favor of
the standard is_kdump_kernel(), this flag only controls run without
relocating the kernel to PHYSICAL_START (0), so rename it __run_at_load.

Move the flag to 0x5c, 1 word before the secondary cpu entry point at
0x60.  Use the copy at address 0 not the one in the base kernel image to
make it easier on kexec-tools.  Initialize it with "run0" to say it will
run at 0 unless it is set to 1.  It only exists if we are relocatable.

Signed-off-by: Milton Miller <miltonm@bga.com>
---
I left it global so it appears that way in System.map, but it would
not need to be.

I kept the guards with CONFIG_CRASH_DUMP for now.  They could be relaxed
to just CONFIG_RELOCATABLE.

Tested with normal kexec (kernel moved to 0) and a custom boot-loader
(kernel stayed at loaded 16MB start).

Index: next.git/arch/powerpc/kernel/head_64.S
===================================================================
--- next.git.orig/arch/powerpc/kernel/head_64.S	2008-10-22 04:30:08.000000000 -0500
+++ next.git/arch/powerpc/kernel/head_64.S	2008-10-22 04:59:55.000000000 -0500
@@ -97,12 +97,6 @@ __secondary_hold_spinloop:
 __secondary_hold_acknowledge:
 	.llong	0x0
 
-	/* This flag is set by purgatory if we should be a kdump kernel. */
-	/* Do not move this variable as purgatory knows about it. */
-	.globl	__kdump_flag
-__kdump_flag:
-	.llong	0x0
-
 #ifdef CONFIG_PPC_ISERIES
 	/*
 	 * At offset 0x20, there is a pointer to iSeries LPAR data.
@@ -112,6 +106,20 @@ __kdump_flag:
 	.llong hvReleaseData-KERNELBASE
 #endif /* CONFIG_PPC_ISERIES */
 
+#ifdef CONFIG_CRASH_DUMP
+	/* This flag is set to 1 by a loader if the kernel should run
+	 * at the loaded address instead of the linked address.  This
+	 * is used by kexec-tools to keep the the kdump kernel in the
+	 * crash_kernel region.  The loader is responsible for
+	 * observing the alignment requirement.
+	 */
+	/* Do not move this variable as kexec-tools knows about it. */
+	. = 0x5c
+	.globl	__run_at_load
+__run_at_load:
+	.long	0x72756e30	/* "run0" -- relocate to 0 by default */
+#endif
+
 	. = 0x60
 /*
  * The following code is used to hold secondary processors
@@ -1391,8 +1399,8 @@ _STATIC(__after_prom_start)
 	lis	r25,PAGE_OFFSET@highest	/* compute virtual base of kernel */
 	sldi	r25,r25,32
 #ifdef CONFIG_CRASH_DUMP
-	ld	r7,__kdump_flag-_stext(r26)
-	cmpldi	cr0,r7,1	/* kdump kernel ? - stay where we are */
+	lwz	r7,__run_at_load-_stext(0)
+	cmplwi	cr0,r7,1	/* kdump kernel ? - stay where we are */
 	bne	1f
 	add	r25,r25,r26
 #endif
@@ -1416,11 +1424,11 @@ _STATIC(__after_prom_start)
 #ifdef CONFIG_CRASH_DUMP
 /*
  * Check if the kernel has to be running as relocatable kernel based on the
- * variable __kdump_flag, if it is set the kernel is treated as relocatable
+ * variable __run_at_load, if it is set the kernel is treated as relocatable
  * kernel, otherwise it will be moved to PHYSICAL_START
  */
-	ld	r7,__kdump_flag-_stext(r26)
-	cmpldi	cr0,r7,1
+	lwz	r7,__run_at_load-_stext(0)
+	cmplwi	cr0,r7,1
 	bne	3f
 
 	li	r5,__end_interrupts - _stext	/* just copy interrupts */

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[PATCH 1/2 kexec-tools] ppc64: new relocatble kernel activation ABI

[Milton Miller]

The updates kexec-tools to match the kernel after the patches

"kexec exit should not use magic numbers" and 

"better flag for running relocatable" are applied.



Signed-off-by: Milton Miller <miltonm@bga.com>
---
Still proposed change

Index: kexec-tools/purgatory/arch/ppc64/v2wrap.S
===================================================================
--- kexec-tools.orig/purgatory/arch/ppc64/v2wrap.S	2008-10-22 06:14:44.000000000 -0500
+++ kexec-tools/purgatory/arch/ppc64/v2wrap.S	2008-10-22 06:14:48.000000000 -0500
@@ -45,11 +45,13 @@
 	oris    rn,rn,name##@h;         \
 	ori     rn,rn,name##@l
 
-#define KDUMP_SIGNATURE 0xfeed1234
-
 	.machine ppc64
 	.globl purgatory_start
 purgatory_start:	b	master
+	.org purgatory_start + 0x5c     # ABI: possible run_at_load flag at 0x5c
+run_at_load:
+	.long 0
+	.size run_at_load, . - run_at_load
 	.org purgatory_start + 0x60     # ABI: slaves start at 60 with r3=phys
 slave:	b $
 	.org purgatory_start + 0x100    # ABI: end of copied region
@@ -65,7 +67,6 @@ master:
 	isync
 	mr      17,3            # save cpu id to r17
 	mr      15,4            # save physical address in reg15
-	mr      18,6            # save kdump flag in reg18
 
 	LOADADDR(6,my_toc)
 	ld      2,0(6)          #setup toc
@@ -96,14 +97,6 @@ master:
 	mtctr	4		# prepare branch too
 	mr      3,16            # restore dt address
 
-	LOADADDR(6,KDUMP_SIGNATURE)
-	cmpd	18,6
-	bne	regular
-	li	7,1
-	std	7,24(4)		# mark kdump flag at kernel
-regular:
-	lwz	7,0(4)		# get the first instruction that we stole
-	stw	7,0(0)		# and put it in the slave loop at 0
 				# skip cache flush, do we care?
 
 	bctr			# start kernel
Index: kexec-tools/kexec/arch/ppc64/crashdump-ppc64.h
===================================================================
--- kexec-tools.orig/kexec/arch/ppc64/crashdump-ppc64.h	2008-10-22 06:14:44.000000000 -0500
+++ kexec-tools/kexec/arch/ppc64/crashdump-ppc64.h	2008-10-22 06:14:48.000000000 -0500
@@ -23,6 +23,8 @@ void add_usable_mem_rgns(unsigned long l
 #define _ALIGN_UP(addr,size)	(((addr)+((size)-1))&(~((size)-1)))
 #define _ALIGN_DOWN(addr,size)	((addr)&(~((size)-1)))
 
+#define KERNEL_RUN_AT_ZERO_MAGIC 0x72756e30	/* "run0" */
+
 extern uint64_t crash_base;
 extern uint64_t crash_size;
 extern unsigned int rtas_base;
Index: kexec-tools/kexec/arch/ppc64/kexec-elf-ppc64.c
===================================================================
--- kexec-tools.orig/kexec/arch/ppc64/kexec-elf-ppc64.c	2008-10-22 06:14:44.000000000 -0500
+++ kexec-tools/kexec/arch/ppc64/kexec-elf-ppc64.c	2008-10-22 06:14:48.000000000 -0500
@@ -93,6 +93,7 @@ int elf_ppc64_load(int argc, char **argv
 	uint64_t my_stack, my_backup_start;
 	uint64_t toc_addr;
 	unsigned int slave_code[256/sizeof (unsigned int)], master_entry;
+	unsigned int run_at_load;
 
 #define OPT_APPEND     (OPT_ARCH_MAX+0)
 #define OPT_RAMDISK     (OPT_ARCH_MAX+1)
@@ -307,6 +308,18 @@ int elf_ppc64_load(int argc, char **argv
 		my_backup_start = info->backup_start;
 		elf_rel_set_symbol(&info->rhdr, "backup_start",
 				&my_backup_start, sizeof(my_backup_start));
+
+		/* Tell relocatable kernel to run at load address
+		 * via word before slave code in purgatory
+		 */
+
+		elf_rel_get_symbol(&info->rhdr, "run_at_load", &run_at_load,
+				sizeof(run_at_load));
+		if (run_at_load == KERNEL_RUN_AT_ZERO_MAGIC)
+			run_at_load = 1;
+			/* else it should be a fixed offset image */
+		elf_rel_set_symbol(&info->rhdr, "run_at_load", &run_at_load,
+				sizeof(run_at_load));
 	}
 
 	/* Set stack address */
@@ -325,10 +338,13 @@ int elf_ppc64_load(int argc, char **argv
 	my_backup_start = 0;
 	my_stack = 0;
 	toc_addr = 0;
+	run_at_load = 0;
 
 	elf_rel_get_symbol(&info->rhdr, "kernel", &my_kernel, sizeof(my_kernel));
 	elf_rel_get_symbol(&info->rhdr, "dt_offset", &my_dt_offset,
 				sizeof(my_dt_offset));
+	elf_rel_get_symbol(&info->rhdr, "run_at_load", &run_at_load,
+				sizeof(run_at_load));
 	elf_rel_get_symbol(&info->rhdr, "panic_kernel", &my_panic_kernel,
 				sizeof(my_panic_kernel));
 	elf_rel_get_symbol(&info->rhdr, "backup_start", &my_backup_start,
@@ -341,6 +357,7 @@ int elf_ppc64_load(int argc, char **argv
 	fprintf(stderr, "kernel is %llx\n", (unsigned long long)my_kernel);
 	fprintf(stderr, "dt_offset is %llx\n",
 		(unsigned long long)my_dt_offset);
+	fprintf(stderr, "run_at_load flag is %x\n", run_at_load);
 	fprintf(stderr, "panic_kernel is %x\n", my_panic_kernel);
 	fprintf(stderr, "backup_start is %llx\n",
 		(unsigned long long)my_backup_start);

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[PATCH 2/2 kexec-tools] ppc64: segemments are sorted

[Milton Miller]

Every time add_segment is called, the segments are sorted.  If the first
hole in memory is not big enough for the kernel then something besides
the kernel may be at 

Signed-off-by: Milton Miller <miltonm@bga.com>
---
Found during custom environment testing with several reserved blocks of
memory, not the usual case.

Index: kexec-tools/kexec/arch/ppc64/kexec-elf-ppc64.c
===================================================================
--- kexec-tools.orig/kexec/arch/ppc64/kexec-elf-ppc64.c	2008-10-22 06:14:48.000000000 -0500
+++ kexec-tools/kexec/arch/ppc64/kexec-elf-ppc64.c	2008-10-22 06:14:54.000000000 -0500
@@ -86,7 +86,7 @@ int elf_ppc64_load(int argc, char **argv
 	size_t size;
 	uint64_t *rsvmap_ptr;
 	struct bootblock *bb_ptr;
-	unsigned int nr_segments, i;
+	unsigned int i;
 	int result, opt;
 	uint64_t my_kernel, my_dt_offset;
 	unsigned int my_panic_kernel;
@@ -187,7 +187,7 @@ int elf_ppc64_load(int argc, char **argv
 	if (size > phdr->p_memsz)
 		size = phdr->p_memsz;
 
-	hole_addr = (uint64_t)locate_hole(info, size, 0, 0,
+	my_kernel = hole_addr = (uint64_t)locate_hole(info, size, 0, 0,
 			max_addr, 1);
 	ehdr.e_phdr[0].p_paddr = hole_addr;
 	result = elf_exec_load(&ehdr, info);
@@ -233,12 +233,10 @@ int elf_ppc64_load(int argc, char **argv
 			return -1;
 		}
 		seg_buf = (unsigned char *)slurp_file(ramdisk, &seg_size);
-		add_buffer(info, seg_buf, seg_size, seg_size, 0, 0, max_addr, 1);
-		hole_addr = (uintptr_t)
-			info->segment[info->nr_segments-1].mem;
+		hole_addr = add_buffer(info, seg_buf, seg_size, seg_size,
+			0, 0, max_addr, 1);
 		initrd_base = hole_addr;
-		initrd_size = (uint64_t)
-			info->segment[info->nr_segments-1].memsz;
+		initrd_size = seg_size;
 	} /* ramdisk */
 
 	if (devicetreeblob) {
@@ -248,16 +246,18 @@ int elf_ppc64_load(int argc, char **argv
 		/* Grab device tree from buffer */
 		blob_buf =
 			(unsigned char *)slurp_file(devicetreeblob, &blob_size);
-		add_buffer(info, blob_buf, blob_size, blob_size, 0, 0,
-				max_addr, -1);
+		my_dt_offset = add_buffer(info, blob_buf, blob_size, blob_size,
+				0, 0, max_addr, -1);
 
+		seg_buf = blob_buf;
+		seg_size = blob_size;
 	} else {
 		/* create from fs2dt */
 		seg_buf = NULL;
 		seg_size = 0;
 		create_flatten_tree(info, (unsigned char **)&seg_buf,
 				(unsigned long *)&seg_size,cmdline);
-		add_buffer(info, seg_buf, seg_size, seg_size,
+		my_dt_offset = add_buffer(info, seg_buf, seg_size, seg_size,
 				0, 0, max_addr, -1);
 	}
 
@@ -265,27 +265,20 @@ int elf_ppc64_load(int argc, char **argv
 	 * find last entry (both 0) in the reserve mem list.  Assume DT
 	 * entry is before this one
 	 */
-	bb_ptr = (struct bootblock *)(
-		(unsigned char *)info->segment[(info->nr_segments)-1].buf);
-	rsvmap_ptr = (uint64_t *)(
-		(unsigned char *)info->segment[(info->nr_segments)-1].buf +
-		bb_ptr->off_mem_rsvmap);
+	bb_ptr = (struct bootblock *)(seg_buf);
+	rsvmap_ptr = (uint64_t *)
+		(((char *)seg_buf) + bb_ptr->off_mem_rsvmap);
 	while (*rsvmap_ptr || *(rsvmap_ptr+1))
 		rsvmap_ptr += 2;
 	rsvmap_ptr -= 2;
-	*rsvmap_ptr = (uintptr_t)(
-		info->segment[(info->nr_segments)-1].mem);
+	*rsvmap_ptr = my_dt_offset;
 	rsvmap_ptr++;
 	*rsvmap_ptr = (uint64_t)bb_ptr->totalsize;
 
-	nr_segments = info->nr_segments;
-
 	/* Set kernel */
-	my_kernel = (uintptr_t)info->segment[0].mem;
 	elf_rel_set_symbol(&info->rhdr, "kernel", &my_kernel, sizeof(my_kernel));
 
 	/* Set dt_offset */
-	my_dt_offset = (uintptr_t)info->segment[nr_segments-1].mem;
 	elf_rel_set_symbol(&info->rhdr, "dt_offset", &my_dt_offset,
 				sizeof(my_dt_offset));
 
@@ -293,7 +286,7 @@ int elf_ppc64_load(int argc, char **argv
 	elf_rel_get_symbol(&info->rhdr, "purgatory_start", slave_code,
 			sizeof(slave_code));
 	master_entry = slave_code[0];
-	memcpy(slave_code, info->segment[0].buf, sizeof(slave_code));
+	memcpy(slave_code, phdr->p_data, sizeof(slave_code));
 	slave_code[0] = master_entry;
 	elf_rel_set_symbol(&info->rhdr, "purgatory_start", slave_code,
 				sizeof(slave_code));
@@ -366,7 +359,7 @@ int elf_ppc64_load(int argc, char **argv
 	fprintf(stderr, "purgatory size is %zu\n", purgatory_size);
 #endif
 
-	for (i = 0; i < nr_segments; i++)
+	for (i = 0; i < info->nr_segments; i++)
 		fprintf(stderr, "segment[%d].mem:%p memsz:%zu\n", i,
 			info->segment[i].mem, info->segment[i].memsz);
 

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[PATCH 1/3] powerpc: kexec exit should not use magic numbers

[Milton Miller]

The relocatable kernel kdump patch (54622f10a6aabb8bb2bdacf3dd070046f03dc246)
added a magic flag value in a register to tell purgatory that it should
be a panic kernel.  This part is wrong and is reverted by this patch.

The kernel gets a list of memory blocks and a entry point from user space.
Its job is to copy the blocks into place and then branch to the designated
entry point (after turning "off" the mmu).

The user space tool inserts a trampoline, called purgatory, that runs
before the user supplied code.   Its job is to establish the entry
environment for the new kernel or other application based on the contents
of memory.  The purgatory code is compiled and embedded in the tool,
where it is later patched using the elf symbol table using elf symbols.

Since the tool knows it is creating a purgatory that will run after a
kernel crash, it should just patch purgatory (or the kernel directly)
if something needs to happen.

Signed-off-by: Milton Miller <miltonm@bga.com>
---
keep the whitespace fix at if(crashing_cpu == -1)

Index: next.git/arch/powerpc/include/asm/kdump.h
===================================================================
--- next.git.orig/arch/powerpc/include/asm/kdump.h	2008-10-22 06:53:22.000000000 -0500
+++ next.git/arch/powerpc/include/asm/kdump.h	2008-10-22 06:54:12.000000000 -0500
@@ -9,12 +9,6 @@
  * Reserve to the end of the FWNMI area, see head_64.S */
 #define KDUMP_RESERVE_LIMIT	0x10000 /* 64K */
 
-/*
- * Used to differentiate between relocatable kdump kernel and other
- * kernels
- */
-#define KDUMP_SIGNATURE	0xfeed1234
-
 #ifdef CONFIG_CRASH_DUMP
 
 #define KDUMP_TRAMPOLINE_START	0x0100
Index: next.git/arch/powerpc/kernel/machine_kexec_64.c
===================================================================
--- next.git.orig/arch/powerpc/kernel/machine_kexec_64.c	2008-10-22 06:53:22.000000000 -0500
+++ next.git/arch/powerpc/kernel/machine_kexec_64.c	2008-10-22 06:54:12.000000000 -0500
@@ -255,14 +255,11 @@ static union thread_union kexec_stack
 /* Our assembly helper, in kexec_stub.S */
 extern NORET_TYPE void kexec_sequence(void *newstack, unsigned long start,
 					void *image, void *control,
-					void (*clear_all)(void),
-					unsigned long kdump_flag) ATTRIB_NORET;
+					void (*clear_all)(void)) ATTRIB_NORET;
 
 /* too late to fail here */
 void default_machine_kexec(struct kimage *image)
 {
-	unsigned long kdump_flag = 0;
-
 	/* prepare control code if any */
 
 	/*
@@ -275,8 +272,6 @@ void default_machine_kexec(struct kimage
 
 	if (crashing_cpu == -1)
 		kexec_prepare_cpus();
-	else
-		kdump_flag = KDUMP_SIGNATURE;
 
 	/* switch to a staticly allocated stack.  Based on irq stack code.
 	 * XXX: the task struct will likely be invalid once we do the copy!
@@ -289,7 +284,7 @@ void default_machine_kexec(struct kimage
 	 */
 	kexec_sequence(&kexec_stack, image->start, image,
 			page_address(image->control_code_page),
-			ppc_md.hpte_clear_all, kdump_flag);
+			ppc_md.hpte_clear_all);
 	/* NOTREACHED */
 }
 
Index: next.git/arch/powerpc/kernel/misc_64.S
===================================================================
--- next.git.orig/arch/powerpc/kernel/misc_64.S	2008-10-22 06:53:22.000000000 -0500
+++ next.git/arch/powerpc/kernel/misc_64.S	2008-10-22 06:54:12.000000000 -0500
@@ -611,12 +611,10 @@ real_mode:	/* assume normal blr return *
 
 
 /*
- * kexec_sequence(newstack, start, image, control, clear_all(), kdump_flag)
+ * kexec_sequence(newstack, start, image, control, clear_all())
  *
  * does the grungy work with stack switching and real mode switches
  * also does simple calls to other code
- *
- * kdump_flag says whether the next kernel should be a kdump kernel.
  */
 
 _GLOBAL(kexec_sequence)
@@ -649,7 +647,7 @@ _GLOBAL(kexec_sequence)
 	mr	r29,r5			/* image (virt) */
 	mr	r28,r6			/* control, unused */
 	mr	r27,r7			/* clear_all() fn desc */
-	mr	r26,r8			/* kdump flag */
+	mr	r26,r8			/* spare */
 	lhz	r25,PACAHWCPUID(r13)	/* get our phys cpu from paca */
 
 	/* disable interrupts, we are overwriting kernel data next */
@@ -711,6 +709,5 @@ _GLOBAL(kexec_sequence)
 	mr	r4,r30	# start, aka phys mem offset
 	mtlr	4
 	li	r5,0
-	mr	r6,r26			/* kdump_flag */
-	blr	/* image->start(physid, image->start, 0, kdump_flag); */
+	blr	/* image->start(physid, image->start, 0); */
 #endif /* CONFIG_KEXEC */

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Re: [PATCH 2/2 kexec-tools] ppc64: segemments are sorted

[Milton Miller]

On Oct 22, 2008, at 3:39 PM, Milton Miller wrote:

> Every time add_segment is called, the segments are sorted.  If the 
> first
> hole in memory is not big enough for the kernel then something besides
> the kernel may be at

info->segment[0].

> ---
> Found during custom environment testing with several reserved blocks of
> memory, not the usual case.

milton


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Re: [PATCH 1/3] powerpc: kexec exit should not use magic numbers

[Simon Horman]

[ Added Mohan Kumar to CC list ]

On Wed, Oct 22, 2008 at 03:39:18PM -0500, Milton Miller wrote:
> The relocatable kernel kdump patch (54622f10a6aabb8bb2bdacf3dd070046f03dc246)
> added a magic flag value in a register to tell purgatory that it should
> be a panic kernel.  This part is wrong and is reverted by this patch.
> 
> The kernel gets a list of memory blocks and a entry point from user space.
> Its job is to copy the blocks into place and then branch to the designated
> entry point (after turning "off" the mmu).
> 
> The user space tool inserts a trampoline, called purgatory, that runs
> before the user supplied code.   Its job is to establish the entry
> environment for the new kernel or other application based on the contents
> of memory.  The purgatory code is compiled and embedded in the tool,
> where it is later patched using the elf symbol table using elf symbols.
> 
> Since the tool knows it is creating a purgatory that will run after a
> kernel crash, it should just patch purgatory (or the kernel directly)
> if something needs to happen.

Hi Milton,

All of these patches look fine to me.

On the kernel side:
Acked-by: Simon Horman <horms@verge.net.au>

On the kexec-tools side:
I'd rather wait until the kernel changes get merged before merging
the kexec-tools portion. Please ping me at that point.


I'd like to note that these changes really ought to go into the same kernel
(and kexec-tools) release that the relocateable kdump patches as they will
introduce incompatibility. For example, crash-dump kernels with only the
relocatable kdump changes will not be usable if the first-kernel includes
these changes. I think that means that this needs to go into 2.6.28 -
assuming that Linus accepts the pull request than Ben Herrenschmidt sent
recently.

-- 
Simon Horman
  VA Linux Systems Japan K.K., Sydney, Australia Satellite Office
  H: www.vergenet.net/~horms/             W: www.valinux.co.jp/en


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Re: [PATCH 3/3] powerpc/ppc64/kdump: better flag for running relocatable

[Michael Neuling]

In message <kexec-kern-2@bga.com> you wrote:
> The __kdump_flag ABI is overly constraining for future development.  
> 
> As of 2.6.27, the kernel entry point has 4 constraints:  Offset 0 is
> the starting point for the master (boot) cpu (entered with r3 pointing
> to the device tree structure), offset 0x60 is code for the slave cpus
> (entered with r3 set to their device tree physical id), offset 0x20 is
> used by the iseries hypervisor, and secondary cpus must be well behaved
> when the first 256 bytes are copied to address 0.
> 
> Placing the __kdump_flag at 0x18 is bad because:
> 
> - It was taking the last 8 bytes before the iseries hypervisor data.  
> - It was 8 bytes for a boolean flag
> - It had no way of identifying that the flag was present
> - It does leave any room for the master to add any additional code
>   before branching, which hurts debug.
> - It will be unnecessarily hard for 32 bit code to be common (8 bytes)
> 
> Now that we have eliminated the use of __kdump_flag in favor of
> the standard is_kdump_kernel(), this flag only controls run without
> relocating the kernel to PHYSICAL_START (0), so rename it __run_at_load.
> 
> Move the flag to 0x5c, 1 word before the secondary cpu entry point at
> 0x60.  Use the copy at address 0 not the one in the base kernel image to
> make it easier on kexec-tools.  Initialize it with "run0" to say it will
> run at 0 unless it is set to 1.  It only exists if we are relocatable.
> 
> Signed-off-by: Milton Miller <miltonm@bga.com>
> ---
> I left it global so it appears that way in System.map, but it would
> not need to be.
> 
> I kept the guards with CONFIG_CRASH_DUMP for now.  They could be relaxed
> to just CONFIG_RELOCATABLE.
> 
> Tested with normal kexec (kernel moved to 0) and a custom boot-loader
> (kernel stayed at loaded 16MB start).
> 
> Index: next.git/arch/powerpc/kernel/head_64.S
> ===================================================================
> --- next.git.orig/arch/powerpc/kernel/head_64.S	2008-10-22 04:30:08.000
000000 -0500
> +++ next.git/arch/powerpc/kernel/head_64.S	2008-10-22 04:59:55.000000000 -
0500
> @@ -97,12 +97,6 @@ __secondary_hold_spinloop:
>  __secondary_hold_acknowledge:
>  	.llong	0x0
>  
> -	/* This flag is set by purgatory if we should be a kdump kernel. */
> -	/* Do not move this variable as purgatory knows about it. */
> -	.globl	__kdump_flag
> -__kdump_flag:
> -	.llong	0x0
> -
>  #ifdef CONFIG_PPC_ISERIES
>  	/*
>  	 * At offset 0x20, there is a pointer to iSeries LPAR data.
> @@ -112,6 +106,20 @@ __kdump_flag:
>  	.llong hvReleaseData-KERNELBASE
>  #endif /* CONFIG_PPC_ISERIES */
>  
> +#ifdef CONFIG_CRASH_DUMP
> +	/* This flag is set to 1 by a loader if the kernel should run
> +	 * at the loaded address instead of the linked address.  This
> +	 * is used by kexec-tools to keep the the kdump kernel in the
> +	 * crash_kernel region.  The loader is responsible for
> +	 * observing the alignment requirement.
> +	 */
> +	/* Do not move this variable as kexec-tools knows about it. */
> +	. = 0x5c
> +	.globl	__run_at_load
> +__run_at_load:
> +	.long	0x72756e30	/* "run0" -- relocate to 0 by default */
> +#endif
> +
>  	. = 0x60
>  /*
>   * The following code is used to hold secondary processors
> @@ -1391,8 +1399,8 @@ _STATIC(__after_prom_start)
>  	lis	r25,PAGE_OFFSET@highest	/* compute virtual base of kernel */
>  	sldi	r25,r25,32
>  #ifdef CONFIG_CRASH_DUMP
> -	ld	r7,__kdump_flag-_stext(r26)
> -	cmpldi	cr0,r7,1	/* kdump kernel ? - stay where we are */
> +	lwz	r7,__run_at_load-_stext(0)
> +	cmplwi	cr0,r7,1	/* kdump kernel ? - stay where we are */

Do we really want the flag to always be at 0x5c not 0x5c + kernel offset?

Also, comment "kdump kernel" needs to be updated to reflect the new
name.  

Other than that, the patch series works for me.

Mikey

>  	bne	1f
>  	add	r25,r25,r26
>  #endif
> @@ -1416,11 +1424,11 @@ _STATIC(__after_prom_start)
>  #ifdef CONFIG_CRASH_DUMP
>  /*
>   * Check if the kernel has to be running as relocatable kernel based on the
> - * variable __kdump_flag, if it is set the kernel is treated as relocatable
> + * variable __run_at_load, if it is set the kernel is treated as relocatable
>   * kernel, otherwise it will be moved to PHYSICAL_START
>   */
> -	ld	r7,__kdump_flag-_stext(r26)
> -	cmpldi	cr0,r7,1
> +	lwz	r7,__run_at_load-_stext(0)
> +	cmplwi	cr0,r7,1
>  	bne	3f
>  
>  	li	r5,__end_interrupts - _stext	/* just copy interrupts */
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@ozlabs.org
> https://ozlabs.org/mailman/listinfo/linuxppc-dev
> 

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Re: [PATCH 3/3] powerpc/ppc64/kdump: better flag for running relocatable

[Paul Mackerras]

Milton Miller writes:

> Move the flag to 0x5c, 1 word before the secondary cpu entry point at
> 0x60.  Use the copy at address 0 not the one in the base kernel image to
> make it easier on kexec-tools.

Why is it easier on kexec-tools?  Doesn't kexec-tools know where it
put the kernel?

I'd much rather keep the flag inside the kdump kernel image, rather
than having kexec/kdump start using random fixed locations outside the
new kernel image.

Paul.

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Re: [PATCH 3/3] powerpc/ppc64/kdump: better flag for running relocatable

[Paul Mackerras]

Paul Mackerras writes:
> Milton Miller writes:
> 
> > Move the flag to 0x5c, 1 word before the secondary cpu entry point at
> > 0x60.  Use the copy at address 0 not the one in the base kernel image to
> > make it easier on kexec-tools.
> 
> Why is it easier on kexec-tools?  Doesn't kexec-tools know where it
> put the kernel?
> 
> I'd much rather keep the flag inside the kdump kernel image, rather
> than having kexec/kdump start using random fixed locations outside the
> new kernel image.

In fact the cliching argument is that when the kernel is loaded by OF
or yaboot, we have no way to tell what will be at location 0x5c,
whereas we know that the word at offset 0x5c in the kernel image will
have been initialized to 0.  So we had better put the flag inside the
kernel image.

Paul.

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Re: [PATCH 3/3] powerpc/ppc64/kdump: better flag for running relocatable

[Mohan Kumar M]

Hi Milton,

My suggestions:

Milton Miller wrote:
> The __kdump_flag ABI is overly constraining for future development.  
> 
> As of 2.6.27, the kernel entry point has 4 constraints:  Offset 0 is
> the starting point for the master (boot) cpu (entered with r3 pointing
> to the device tree structure), offset 0x60 is code for the slave cpus
> (entered with r3 set to their device tree physical id), offset 0x20 is
> used by the iseries hypervisor, and secondary cpus must be well behaved
> when the first 256 bytes are copied to address 0.
> 
> Placing the __kdump_flag at 0x18 is bad because:
> 
> - It was taking the last 8 bytes before the iseries hypervisor data.  
> - It was 8 bytes for a boolean flag
> - It had no way of identifying that the flag was present
> - It does leave any room for the master to add any additional code
>   before branching, which hurts debug.
> - It will be unnecessarily hard for 32 bit code to be common (8 bytes)
> 
> Now that we have eliminated the use of __kdump_flag in favor of
> the standard is_kdump_kernel(), this flag only controls run without
> relocating the kernel to PHYSICAL_START (0), so rename it __run_at_load.
>
We could try both of our approaches. Instead of passing the information 
that next kernel should be relocatable from kexec_sequence to purgatory 
code, we will do it from kexec-tools path (following your approach). But 
instead of setting the __run_at_load value in the purgatory code (ie at 
physical address 0x5c), we will set the variable __run_at_load at kernel 
  image itself.

i.e.,
[code snip 1]
	lwz	r7,__run_at_load-_stext(r26)
	cmplwi	cr0,r7,1	/* kdump kernel ? - stay where we are */
  	bne	1f
  	add	r25,r25,r26

	lwz	r7,__run_at_load-_stext(r26)
	cmplwi	cr0,r7,1
  	bne	3f

kexec-tools
[code snip 2]
	LOADADDR(6,run_at_load)
	ld	18,0(6)
	cmpd	18,1
	bne	skip
	li	7,1
	stw	7,92(4)		# mark __run_at_load flag at kernel
skip:
	lwz	7,0(4)		# get the first instruction that we stole
	stw	7,0(0)		# and put it in the slave loop at 0
  				# skip cache flush, do we care?

[code snip 3]
	if (info->kexec_flags & KEXEC_ON_CRASH) {
		....
		elf_rel_set_symbol(&info->rhdr, "run_at_load",
                                 &my_run_at_load, 							 
sizeof(my_run_at_load));
	}

Using this approach we are not breaking the kexec_sequence ABI and we 
directly modifying the flag in kernel image.

Regards,
Mohan.

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[PATCH 3/3] powerpc/ppc64/kdump: better flag for running relocatable

[Michael Neuling]

From: Milton Miller <miltonm@bga.com>

The __kdump_flag ABI is overly constraining for future development.  

As of 2.6.27, the kernel entry point has 4 constraints:  Offset 0 is
the starting point for the master (boot) cpu (entered with r3 pointing
to the device tree structure), offset 0x60 is code for the slave cpus
(entered with r3 set to their device tree physical id), offset 0x20 is
used by the iseries hypervisor, and secondary cpus must be well behaved
when the first 256 bytes are copied to address 0.

Placing the __kdump_flag at 0x18 is bad because:

- It was taking the last 8 bytes before the iseries hypervisor data.  
- It was 8 bytes for a boolean flag
- It had no way of identifying that the flag was present
- It does leave any room for the master to add any additional code
  before branching, which hurts debug.
- It will be unnecessarily hard for 32 bit code to be common (8 bytes)

Now that we have eliminated the use of __kdump_flag in favor of
the standard is_kdump_kernel(), this flag only controls run without
relocating the kernel to PHYSICAL_START (0), so rename it __run_at_load.

Move the flag to 0x5c, 1 word before the secondary cpu entry point at
0x60.  Initialize it with "run0" to say it will run at 0 unless it is
set to 1.  It only exists if we are relocatable.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Michael Neuling <mikey@neuling.org>
---
 arch/powerpc/kernel/head_64.S |   30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

As discussed, this changes the __run_at_load location to 
0x5c + load offset rather than 0x5c + 0.

Index: linux-2.6-ozlabs/arch/powerpc/kernel/head_64.S
===================================================================
--- linux-2.6-ozlabs.orig/arch/powerpc/kernel/head_64.S
+++ linux-2.6-ozlabs/arch/powerpc/kernel/head_64.S
@@ -104,12 +104,6 @@ __secondary_hold_spinloop:
 __secondary_hold_acknowledge:
 	.llong	0x0
 
-	/* This flag is set by purgatory if we should be a kdump kernel. */
-	/* Do not move this variable as purgatory knows about it. */
-	.globl	__kdump_flag
-__kdump_flag:
-	.llong	0x0
-
 #ifdef CONFIG_PPC_ISERIES
 	/*
 	 * At offset 0x20, there is a pointer to iSeries LPAR data.
@@ -119,6 +113,20 @@ __kdump_flag:
 	.llong hvReleaseData-KERNELBASE
 #endif /* CONFIG_PPC_ISERIES */
 
+#ifdef CONFIG_CRASH_DUMP
+	/* This flag is set to 1 by a loader if the kernel should run
+	 * at the loaded address instead of the linked address.  This
+	 * is used by kexec-tools to keep the the kdump kernel in the
+	 * crash_kernel region.  The loader is responsible for
+	 * observing the alignment requirement.
+	 */
+	/* Do not move this variable as kexec-tools knows about it. */
+	. = 0x5c
+	.globl	__run_at_load
+__run_at_load:
+	.long	0x72756e30	/* "run0" -- relocate to 0 by default */
+#endif
+
 	. = 0x60
 /*
  * The following code is used to hold secondary processors
@@ -1407,8 +1415,8 @@ _STATIC(__after_prom_start)
 	lis	r25,PAGE_OFFSET@highest	/* compute virtual base of kernel */
 	sldi	r25,r25,32
 #ifdef CONFIG_CRASH_DUMP
-	ld	r7,__kdump_flag-_stext(r26)
-	cmpldi	cr0,r7,1	/* kdump kernel ? - stay where we are */
+	lwz	r7,__run_at_load-_stext(r26)
+	cmplwi	cr0,r7,1	/* kdump kernel ? - stay where we are */
 	bne	1f
 	add	r25,r25,r26
 #endif
@@ -1432,11 +1440,11 @@ _STATIC(__after_prom_start)
 #ifdef CONFIG_CRASH_DUMP
 /*
  * Check if the kernel has to be running as relocatable kernel based on the
- * variable __kdump_flag, if it is set the kernel is treated as relocatable
+ * variable __run_at_load, if it is set the kernel is treated as relocatable
  * kernel, otherwise it will be moved to PHYSICAL_START
  */
-	ld	r7,__kdump_flag-_stext(r26)
-	cmpldi	cr0,r7,1
+	lwz	r7,__run_at_load-_stext(r26)
+	cmplwi	cr0,r7,1
 	bne	3f
 
 	li	r5,__end_interrupts - _stext	/* just copy interrupts */

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Re: [PATCH 3/3] powerpc/ppc64/kdump: better flag for running relocatable

[Milton Miller]

On Oct 22, 2008, at 10:43 PM, Paul Mackerras wrote:
> Paul Mackerras writes:
>> Milton Miller writes:
>>> Move the flag to 0x5c, 1 word before the secondary cpu entry point at
>>> 0x60.  Use the copy at address 0 not the one in the base kernel 
>>> image to
>>> make it easier on kexec-tools.
>>
>> Why is it easier on kexec-tools?  Doesn't kexec-tools know where it
>> put the kernel?

The archictecture code calls cross-platform code to identify what is
loaded.   It isn't specified if this is a shared mmap or a read into
a buffer.

>>
>> I'd much rather keep the flag inside the kdump kernel image, rather
>> than having kexec/kdump start using random fixed locations outside the
>> new kernel image.
>
> In fact the cliching argument is that when the kernel is loaded by OF
> or yaboot, we have no way to tell what will be at location 0x5c,
> whereas we know that the word at offset 0x5c in the kernel image will
> have been initialized to 0.  So we had better put the flag inside the
> kernel image.

Well, prom_init will copy the 256 bytes to 0 before the code checks
that location.

However, there is an arguement for using the same code from an epapr
or book-e relocatable, and that would need it at 0.   And today
the kexec tool does not do a shared mmap.  Since the change has
been made, I will make a new patch for kexec-tools.

milton


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Re: [PATCH 3/3] powerpc/ppc64/kdump: better flag for running relocatable

[Milton Miller]

On Oct 23, 2008, at 10:15 AM, Mohan Kumar M wrote:
> Hi Milton,
> My suggestions:
> Milton Miller wrote:
>> The __kdump_flag ABI is overly constraining for future development.
...
>> Now that we have eliminated the use of __kdump_flag in favor of
>> the standard is_kdump_kernel(), this flag only controls run without
>> relocating the kernel to PHYSICAL_START (0), so rename it 
>> __run_at_load.
>>
> We could try both of our approaches. Instead of passing the 
> information that next kernel should be relocatable from kexec_sequence 
> to purgatory code, we will do it from kexec-tools path (following your 
> approach). But instead of setting the __run_at_load value in the 
> purgatory code (ie at physical address 0x5c), we will set the variable 
> __run_at_load at kernel  image itself.
>
> i.e.,
> [code snip 1]
> 	lwz	r7,__run_at_load-_stext(r26)
> 	cmplwi	cr0,r7,1	/* kdump kernel ? - stay where we are */
>  	bne	1f
>  	add	r25,r25,r26
>
> 	lwz	r7,__run_at_load-_stext(r26)
> 	cmplwi	cr0,r7,1
>  	bne	3f
>
> kexec-tools
> [code snip 2]
> 	LOADADDR(6,run_at_load)
> 	ld	18,0(6)
> 	cmpd	18,1
> 	bne	skip
> 	li	7,1
> 	stw	7,92(4)		# mark __run_at_load flag at kernel
> skip:
> 	lwz	7,0(4)		# get the first instruction that we stole
> 	stw	7,0(0)		# and put it in the slave loop at 0
>  				# skip cache flush, do we care?
>
> [code snip 3]
> 	if (info->kexec_flags & KEXEC_ON_CRASH) {
> 		....
> 		elf_rel_set_symbol(&info->rhdr, "run_at_load",
>                                 &my_run_at_load, 							 
> sizeof(my_run_at_load));
> 	}


This elf_rel_set_symbol sets the copy in purgatory,
after we have copied the code from the kernel.  It
is this copy that gets copied to address 0.

However this information is not in the code that
is at the start of the kernel.  We don't have any
symbols for the kernel itself, it might be stripped.
So we can't use the elf_set_symbol api.  (The kernel
may not be relocatable either).

> Using this approach we are not breaking the kexec_sequence
> ABI and we directly modifying the flag in kernel image.
>
> Regards,
> Mohan.

I'll prepare a patch, but it might be a few days
while I catch up from my 2 week vacation.

milton


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Re: [PATCH 3/3] powerpc/ppc64/kdump: better flag for running relocatable

[Mohan Kumar M]

Milton Miller wrote:
> On Oct 23, 2008, at 10:15 AM, Mohan Kumar M wrote:
>> Hi Milton,
>> My suggestions:
>> Milton Miller wrote:
>>
>> i.e.,
>> [code snip 1]
>> 	lwz	r7,__run_at_load-_stext(r26)
>> 	cmplwi	cr0,r7,1	/* kdump kernel ? - stay where we are */
>>  	bne	1f
>>  	add	r25,r25,r26
>>
>> 	lwz	r7,__run_at_load-_stext(r26)
>> 	cmplwi	cr0,r7,1
>>  	bne	3f
>>
>> kexec-tools
>> [code snip 2]
>> 	LOADADDR(6,run_at_load)
>> 	ld	18,0(6)
>> 	cmpd	18,1
>> 	bne	skip
>> 	li	7,1
>> 	stw	7,92(4)		# mark __run_at_load flag at kernel
>> skip:
>> 	lwz	7,0(4)		# get the first instruction that we stole
>> 	stw	7,0(0)		# and put it in the slave loop at 0
>>  				# skip cache flush, do we care?
>>
>> [code snip 3]
>> 	if (info->kexec_flags & KEXEC_ON_CRASH) {
>> 		....
>> 		elf_rel_set_symbol(&info->rhdr, "run_at_load",
>>                                 &my_run_at_load, 							 
>> sizeof(my_run_at_load));
>> 	}
> 
> 
> This elf_rel_set_symbol sets the copy in purgatory,
> after we have copied the code from the kernel.  It
> is this copy that gets copied to address 0.
> 

Yes, elf_ret_symbol sets the copy in purgatory. But the following code 
in purgatory (to be introduced)

  	LOADADDR(6,run_at_load)
  	ld	18,0(6)
  	cmpd	18,1
  	bne	skip
  	li	7,1
  	stw	7,92(4)		# mark __run_at_load flag at kernel

will set the __run_at_load in the kernel image (ie where ever kernel is 
loaded + 0x5c(92). Or am I missing some thing?

> However this information is not in the code that
> is at the start of the kernel.  We don't have any
> symbols for the kernel itself, it might be stripped.
> So we can't use the elf_set_symbol api.  (The kernel
> may not be relocatable either).

Regards,
Mohan.

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Re: [PATCH 3/3] powerpc/ppc64/kdump: better flag for running relocatable

[Milton Miller]

On Nov 10, 2008, at 9:22 AM, Mohan Kumar M wrote:
> Yes, elf_ret_symbol sets the copy in purgatory. But the following code 
> in purgatory (to be introduced)
>
>  	LOADADDR(6,run_at_load)
>  	ld	18,0(6)
>  	cmpd	18,1
>  	bne	skip
>  	li	7,1
>  	stw	7,92(4)		# mark __run_at_load flag at kernel
>
> will set the __run_at_load in the kernel image (ie where ever kernel 
> is loaded + 0x5c(92). Or am I missing some thing?

That would work, but I prefer to keep the change in the userspace side. 
  Partly because I don't want to link setting the relocatable flag to 
purgatory starting a dump kernel, and partly because I think 
kexec-tools should be verifying that the loaded kernel will run where 
it expects, either by it finding the relcatable flag, inspecting the 
elf header for the linked address, or some other method (like elf type 
is dynamic for some platforms).  Oh, and its more readable in C.

If someone adds mmap instead of read files to the common code, then we 
will just have to make sure they use MMAP_PRIVATE instead of 
MMAP_SHARED.  Today its not an issue.

milton


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