[PATCH 2/7] ia64, kexec: Make INIT safe while kdump/kexec

[Hidetoshi Seto]

In panic situation, we may receive INIT while kernel transition,
i.e. from preparation of kdump to bootstrap of kdump kernel.
Since we initialize registers on leave from current kernel, no
longer monarch/slave handlers of current kernel in virtual mode are
called safely.  (In fact system goes hang as far as I confirmed)

How to Reproduce:

  Start kdump
    # echo c > /proc/sysrq-trigger
  Then assert INIT before kdump kernel boots

We can unregister these init handlers from SAL before jumping into
new kernel, however then the INIT will fallback to default behavior,
result in warmboot by SAL (according to the SAL specification) and
we cannot retrieve the crashdump.

Therefore this patch introduces a NOP init handler and register it
to SAL before leave from current kernel, to start kdump safely by
preventing INITs from entering virtual mode and resulting in warmboot.

On the other hand, in case of kexec that not for kdump, it also
has same problem with INIT while kernel transition.
This patch handles this case differently, because for kexec
unregistering handlers will be preferred than registering NOP
handler, since the situation "no handlers registered" is usual
state for kernel's entry.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi at jp.fujitsu.com>
Cc: Vivek Goyal <vgoyal at redhat.com>
Cc: Haren Myneni <hbabu at us.ibm.com>
Cc: kexec at lists.infradead.org
---
 arch/ia64/kernel/machine_kexec.c |   14 ++++++++++++++
 arch/ia64/kernel/mca_asm.S       |   20 ++++++++++++++++++++
 2 files changed, 34 insertions(+), 0 deletions(-)

diff --git a/arch/ia64/kernel/machine_kexec.c b/arch/ia64/kernel/machine_kexec.c
index 0823de1..d35fc39 100644
--- a/arch/ia64/kernel/machine_kexec.c
+++ b/arch/ia64/kernel/machine_kexec.c
@@ -24,6 +24,8 @@
 #include <asm/delay.h>
 #include <asm/meminit.h>
 #include <asm/processor.h>
+#include <asm/sal.h>
+#include <asm/mca.h>
 
 typedef NORET_TYPE void (*relocate_new_kernel_t)(
 					unsigned long indirection_page,
@@ -47,6 +49,8 @@ struct resource boot_param_res = {
         .flags = IORESOURCE_BUSY | IORESOURCE_MEM
 };
 
+/* In mca_asm.S */
+extern void ia64_os_init_on_kdump(void);
 
 /*
  * Do what every setup is needed on image and the
@@ -85,11 +89,21 @@ static void ia64_machine_kexec(struct unw_frame_info *info, void *arg)
 	void *pal_addr = efi_get_pal_addr();
 	unsigned long code_addr = (unsigned long)page_address(image->control_code_page);
 	int ii;
+	u64 fp, gp;
+	ia64_fptr_t *init_handler = (ia64_fptr_t *)ia64_os_init_on_kdump;
 
 	BUG_ON(!image);
 	if (image->type == KEXEC_TYPE_CRASH) {
 		crash_save_this_cpu();
 		current->thread.ksp = (__u64)info->sw - 16;
+
+		/* Register noop init handler */
+		fp = ia64_tpa(init_handler->fp);
+		gp = ia64_tpa(ia64_getreg(_IA64_REG_GP));
+		ia64_sal_set_vectors(SAL_VECTOR_OS_INIT, fp, gp, 0, fp, gp, 0);
+	} else {
+		/* Unregister init handlers of current kernel */
+		ia64_sal_set_vectors(SAL_VECTOR_OS_INIT, 0, 0, 0, 0, 0, 0);
 	}
 
 	/* Interrupts aren't acceptable while we reboot */
diff --git a/arch/ia64/kernel/mca_asm.S b/arch/ia64/kernel/mca_asm.S
index c6ee089..0594c54 100644
--- a/arch/ia64/kernel/mca_asm.S
+++ b/arch/ia64/kernel/mca_asm.S
@@ -40,6 +40,7 @@
 
 	.global ia64_do_tlb_purge
 	.global ia64_os_mca_dispatch
+	.global ia64_os_init_on_kdump
 	.global ia64_os_init_dispatch_monarch
 	.global ia64_os_init_dispatch_slave
 
@@ -299,6 +300,25 @@ END(ia64_os_mca_virtual_begin)
 //StartMain////////////////////////////////////////////////////////////////////
 
 //
+// NOP init handler for kdump.  In panic situation, we may receive INIT
+// while kernel transition.  Since we initialize registers on leave from
+// current kernel, no longer monarch/slave handlers of current kernel in
+// virtual mode are called safely.
+// We can unregister these init handlers from SAL, however then the INIT
+// will result in warmboot by SAL and we cannot retrieve the crashdump.
+// Therefore register this NOP function to SAL, to prevent entering virtual
+// mode and resulting warmboot by SAL.
+//
+ia64_os_init_on_kdump:
+	mov		r8=r0		// IA64_INIT_RESUME
+	mov             r9=r10		// SAL_GP
+	mov		r22=r17		// *minstate
+	;;
+	mov		r10=r0		// return to same context
+	mov		b0=r12		// SAL_CHECK return address
+	br		b0
+
+//
 // SAL to OS entry point for INIT on all processors.  This has been defined for
 // registration purposes with SAL as a part of ia64_mca_init.  Monarch and
 // slave INIT have identical processing, except for the value of the
-- 
1.6.0