powerpc: Support for relocatable kdump kernel

This adds relocatable kernel support for kdump. With this one can
use the same regular kernel to capture the kdump. A signature (0xfeed1234)
is passed in r6 from panic code to the next kernel through kexec_sequence
and purgatory code. The signature is used to differentiate between
kdump kernel and non-kdump kernels.

The purgatory code compares the signature and sets the __kdump_flag in
head_64.S.  During the boot up, kernel code checks __kdump_flag and if it
is set, the kernel will behave as relocatable kdump kernel. This kernel
will boot at the address where it was loaded by kexec-tools ie. at the
address reserved through crashkernel boot parameter.

CONFIG_CRASH_DUMP depends on CONFIG_RELOCATABLE option to build kdump
kernel as relocatable. So the same kernel can be used as production and
kdump kernel.

This patch incorporates the changes suggested by Paul Mackerras to avoid
GOT use and to avoid two copies of the code.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Mohan Kumar M <mohan@in.ibm.com>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 33 insertions, 6 deletions

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 84856bee33a5..69489bd3210c 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -97,6 +97,12 @@ __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.
@@ -1384,7 +1390,13 @@ _STATIC(__after_prom_start)
         /* process relocations for the final address of the kernel */
         lis     r25,PAGE_OFFSET@highest /* compute virtual base of kernel */
         sldi    r25,r25,32
-        mr      r3,r25
+#ifdef CONFIG_CRASH_DUMP
+        ld      r7,__kdump_flag-_stext(r26)
+        cmpldi  cr0,r7,1        /* kdump kernel ? - stay where we are */
+        bne     1f
+        add     r25,r25,r26
+#endif
+1:      mr      r3,r25
         bl      .relocate
 #endif
 
@@ -1398,11 +1410,26 @@ _STATIC(__after_prom_start)
         li      r3,0                    /* target addr */
         mr.     r4,r26                  /* In some cases the loader may  */
         beq     9f                      /* have already put us at zero */
-        lis     r5,(copy_to_here - _stext)@ha
-        addi    r5,r5,(copy_to_here - _stext)@l /* # bytes of memory to copy */
         li      r6,0x100                /* Start offset, the first 0x100 */
                                         /* bytes were copied earlier.    */
 
+#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
+ * kernel, otherwise it will be moved to PHYSICAL_START
+ */
+        ld      r7,__kdump_flag-_stext(r26)
+        cmpldi  cr0,r7,1
+        bne     3f
+
+        li      r5,__end_interrupts - _stext    /* just copy interrupts */
+        b       5f
+3:
+#endif
+        lis     r5,(copy_to_here - _stext)@ha
+        addi    r5,r5,(copy_to_here - _stext)@l /* # bytes of memory to copy */
+
         bl      .copy_and_flush         /* copy the first n bytes        */
                                         /* this includes the code being  */
                                         /* executed here.                */
@@ -1411,15 +1438,15 @@ _STATIC(__after_prom_start)
         mtctr   r8
         bctr
 
+p_end:  .llong  _end - _stext
+
 4:      /* Now copy the rest of the kernel up to _end */
         addis   r5,r26,(p_end - _stext)@ha
         ld      r5,(p_end - _stext)@l(r5)       /* get _end */
-        bl      .copy_and_flush         /* copy the rest */
+5:      bl      .copy_and_flush         /* copy the rest */
 
 9:      b       .start_here_multiplatform
 
-p_end:  .llong  _end - _stext
-
 /*
  * Copy routine used to copy the kernel to start at physical address 0
  * and flush and invalidate the caches as needed.