[PATCH] ia64: Restore registers in the stack on INIT

[Keith Owens]

On Wed, 30 Sep 2009 14:49:25 -0400, 
Takao Indoh <indou.takao at jp.fujitsu.com> wrote:
>Hi all,
>
>When I was investigating vmcore captured by kdump, I noticed that
>the backtrace was sometimes not displayed correctly.
>
>The cause is that pt_regs and switch_stack are not saved in the stack
>when INIT comes during fsys mode. In fsys mode, r13 register does not
>point task_struct of current, so pt_regs and switch_stack are not saved
>because of the following code in arch/ia64/kernel/mca.c.
>
>static struct task_struct *
>ia64_mca_modify_original_stack(struct pt_regs *regs,
>(snip)
>        if (r13 != sos->prev_IA64_KR_CURRENT) {
>                msg = "inconsistent previous current and r13";
>                goto no_mod;
>        }
>
>What I'd like to note here is that there is no way to know what happened
>when original stack is not modified.
>As I wrote above, the registers is not saved in the original stack, and
>moreover, the registers in the per cpu stack are useless since they are
>incomplete. We can't know why backtrace is not displayed. The only thing
>we can get is the message "inconsistent previous current and r13" in the
>mprintk buffer. Something problem happened? Or kernel was just in fsys
>mode? We cannot know.
>
>Solution1:
> The pt_regs in the per cpu stack are incomplete, so fill in the blanks
> with the appropriate registers so that we can debug using them.
>
>Solution2:
> Save the processor min-state(pal_min_state_area_t) somewhere. When
> debugging, user can get register info from it.
>
>I prefer solution1 because it's easy for user to debug. The
>following patch is for solution1. restore_regs(), which is new function
>added by this patch, is just copying registers from pal_min_state
>to pt_regs.
>
>Any comments would be appreciated.
>
>Thanks,
>Takao Indoh
>
>Signed-off-by: Takao Indoh <indou.takao at jp.fujitsu.com>
>---
> arch/ia64/kernel/mca.c |  103 +++++++++++++++++++++------------------
> 1 file changed, 56 insertions(+), 47 deletions(-)
>
>diff -Nurp linux-2.6.31.org/arch/ia64/kernel/mca.c linux-2.6.31/arch/ia64/kernel/mca.c
>--- linux-2.6.31.org/arch/ia64/kernel/mca.c	2009-09-21 17:12:45.000000000 -0400
>+++ linux-2.6.31/arch/ia64/kernel/mca.c	2009-09-24 16:15:05.000000000 -0400
>@@ -887,6 +887,60 @@ ia64_mca_modify_comm(const struct task_s
> 	memcpy(current->comm, comm, sizeof(current->comm));
> }
> 
>+static void
>+restore_regs(struct pt_regs *regs, const pal_min_state_area_t *ms,
>+		unsigned long *nat)

The name 'restore_regs' is too generic and is used in other code,
'finish_pt_regs' might be better.

>+{
>+	const u64 *bank;
>+
>+	/* If ipsr.ic then use pmsa_{iip,ipsr,ifs}, else use
>+	 * pmsa_{xip,xpsr,xfs}
>+	 */
>+	if (ia64_psr(regs)->ic) {
>+		regs->cr_iip = ms->pmsa_iip;
>+		regs->cr_ipsr = ms->pmsa_ipsr;
>+		regs->cr_ifs = ms->pmsa_ifs;
>+	} else {
>+		regs->cr_iip = ms->pmsa_xip;
>+		regs->cr_ipsr = ms->pmsa_xpsr;
>+		regs->cr_ifs = ms->pmsa_xfs;
>+	}
>+	regs->pr = ms->pmsa_pr;
>+	regs->b0 = ms->pmsa_br0;
>+	regs->ar_rsc = ms->pmsa_rsc;
>+	copy_reg(&ms->pmsa_gr[1-1], ms->pmsa_nat_bits, &regs->r1, nat);
>+	copy_reg(&ms->pmsa_gr[2-1], ms->pmsa_nat_bits, &regs->r2, nat);
>+	copy_reg(&ms->pmsa_gr[3-1], ms->pmsa_nat_bits, &regs->r3, nat);
>+	copy_reg(&ms->pmsa_gr[8-1], ms->pmsa_nat_bits, &regs->r8, nat);
>+	copy_reg(&ms->pmsa_gr[9-1], ms->pmsa_nat_bits, &regs->r9, nat);
>+	copy_reg(&ms->pmsa_gr[10-1], ms->pmsa_nat_bits, &regs->r10, nat);
>+	copy_reg(&ms->pmsa_gr[11-1], ms->pmsa_nat_bits, &regs->r11, nat);
>+	copy_reg(&ms->pmsa_gr[12-1], ms->pmsa_nat_bits, &regs->r12, nat);
>+	copy_reg(&ms->pmsa_gr[13-1], ms->pmsa_nat_bits, &regs->r13, nat);
>+	copy_reg(&ms->pmsa_gr[14-1], ms->pmsa_nat_bits, &regs->r14, nat);
>+	copy_reg(&ms->pmsa_gr[15-1], ms->pmsa_nat_bits, &regs->r15, nat);
>+	if (ia64_psr(regs)->bn)
>+		bank = ms->pmsa_bank1_gr;
>+	else
>+		bank = ms->pmsa_bank0_gr;
>+	copy_reg(&bank[16-16], ms->pmsa_nat_bits, &regs->r16, nat);
>+	copy_reg(&bank[17-16], ms->pmsa_nat_bits, &regs->r17, nat);
>+	copy_reg(&bank[18-16], ms->pmsa_nat_bits, &regs->r18, nat);
>+	copy_reg(&bank[19-16], ms->pmsa_nat_bits, &regs->r19, nat);
>+	copy_reg(&bank[20-16], ms->pmsa_nat_bits, &regs->r20, nat);
>+	copy_reg(&bank[21-16], ms->pmsa_nat_bits, &regs->r21, nat);
>+	copy_reg(&bank[22-16], ms->pmsa_nat_bits, &regs->r22, nat);
>+	copy_reg(&bank[23-16], ms->pmsa_nat_bits, &regs->r23, nat);
>+	copy_reg(&bank[24-16], ms->pmsa_nat_bits, &regs->r24, nat);
>+	copy_reg(&bank[25-16], ms->pmsa_nat_bits, &regs->r25, nat);
>+	copy_reg(&bank[26-16], ms->pmsa_nat_bits, &regs->r26, nat);
>+	copy_reg(&bank[27-16], ms->pmsa_nat_bits, &regs->r27, nat);
>+	copy_reg(&bank[28-16], ms->pmsa_nat_bits, &regs->r28, nat);
>+	copy_reg(&bank[29-16], ms->pmsa_nat_bits, &regs->r29, nat);
>+	copy_reg(&bank[30-16], ms->pmsa_nat_bits, &regs->r30, nat);
>+	copy_reg(&bank[31-16], ms->pmsa_nat_bits, &regs->r31, nat);
>+}
>+
> /* On entry to this routine, we are running on the per cpu stack, see
>  * mca_asm.h.  The original stack has not been touched by this event.  Some of
>  * the original stack's registers will be in the RBS on this stack.  This stack
>@@ -921,7 +975,6 @@ ia64_mca_modify_original_stack(struct pt
> 	u64 r12 = ms->pmsa_gr[12-1], r13 = ms->pmsa_gr[13-1];
> 	u64 ar_bspstore = regs->ar_bspstore;
> 	u64 ar_bsp = regs->ar_bspstore + (loadrs >> 16);
>-	const u64 *bank;
> 	const char *msg;
> 	int cpu = smp_processor_id();
> 
>@@ -1024,54 +1077,9 @@ ia64_mca_modify_original_stack(struct pt
> 	p = (char *)r12 - sizeof(*regs);
> 	old_regs = (struct pt_regs *)p;
> 	memcpy(old_regs, regs, sizeof(*regs));
>-	/* If ipsr.ic then use pmsa_{iip,ipsr,ifs}, else use
>-	 * pmsa_{xip,xpsr,xfs}
>-	 */
>-	if (ia64_psr(regs)->ic) {
>-		old_regs->cr_iip = ms->pmsa_iip;
>-		old_regs->cr_ipsr = ms->pmsa_ipsr;
>-		old_regs->cr_ifs = ms->pmsa_ifs;
>-	} else {
>-		old_regs->cr_iip = ms->pmsa_xip;
>-		old_regs->cr_ipsr = ms->pmsa_xpsr;
>-		old_regs->cr_ifs = ms->pmsa_xfs;
>-	}
>-	old_regs->pr = ms->pmsa_pr;
>-	old_regs->b0 = ms->pmsa_br0;
> 	old_regs->loadrs = loadrs;
>-	old_regs->ar_rsc = ms->pmsa_rsc;
> 	old_unat = old_regs->ar_unat;
>-	copy_reg(&ms->pmsa_gr[1-1], ms->pmsa_nat_bits, &old_regs->r1, &old_unat);
>-	copy_reg(&ms->pmsa_gr[2-1], ms->pmsa_nat_bits, &old_regs->r2, &old_unat);
>-	copy_reg(&ms->pmsa_gr[3-1], ms->pmsa_nat_bits, &old_regs->r3, &old_unat);
>-	copy_reg(&ms->pmsa_gr[8-1], ms->pmsa_nat_bits, &old_regs->r8, &old_unat);
>-	copy_reg(&ms->pmsa_gr[9-1], ms->pmsa_nat_bits, &old_regs->r9, &old_unat);
>-	copy_reg(&ms->pmsa_gr[10-1], ms->pmsa_nat_bits, &old_regs->r10, &old_unat);
>-	copy_reg(&ms->pmsa_gr[11-1], ms->pmsa_nat_bits, &old_regs->r11, &old_unat);
>-	copy_reg(&ms->pmsa_gr[12-1], ms->pmsa_nat_bits, &old_regs->r12, &old_unat);
>-	copy_reg(&ms->pmsa_gr[13-1], ms->pmsa_nat_bits, &old_regs->r13, &old_unat);
>-	copy_reg(&ms->pmsa_gr[14-1], ms->pmsa_nat_bits, &old_regs->r14, &old_unat);
>-	copy_reg(&ms->pmsa_gr[15-1], ms->pmsa_nat_bits, &old_regs->r15, &old_unat);
>-	if (ia64_psr(old_regs)->bn)
>-		bank = ms->pmsa_bank1_gr;
>-	else
>-		bank = ms->pmsa_bank0_gr;
>-	copy_reg(&bank[16-16], ms->pmsa_nat_bits, &old_regs->r16, &old_unat);
>-	copy_reg(&bank[17-16], ms->pmsa_nat_bits, &old_regs->r17, &old_unat);
>-	copy_reg(&bank[18-16], ms->pmsa_nat_bits, &old_regs->r18, &old_unat);
>-	copy_reg(&bank[19-16], ms->pmsa_nat_bits, &old_regs->r19, &old_unat);
>-	copy_reg(&bank[20-16], ms->pmsa_nat_bits, &old_regs->r20, &old_unat);
>-	copy_reg(&bank[21-16], ms->pmsa_nat_bits, &old_regs->r21, &old_unat);
>-	copy_reg(&bank[22-16], ms->pmsa_nat_bits, &old_regs->r22, &old_unat);
>-	copy_reg(&bank[23-16], ms->pmsa_nat_bits, &old_regs->r23, &old_unat);
>-	copy_reg(&bank[24-16], ms->pmsa_nat_bits, &old_regs->r24, &old_unat);
>-	copy_reg(&bank[25-16], ms->pmsa_nat_bits, &old_regs->r25, &old_unat);
>-	copy_reg(&bank[26-16], ms->pmsa_nat_bits, &old_regs->r26, &old_unat);
>-	copy_reg(&bank[27-16], ms->pmsa_nat_bits, &old_regs->r27, &old_unat);
>-	copy_reg(&bank[28-16], ms->pmsa_nat_bits, &old_regs->r28, &old_unat);
>-	copy_reg(&bank[29-16], ms->pmsa_nat_bits, &old_regs->r29, &old_unat);
>-	copy_reg(&bank[30-16], ms->pmsa_nat_bits, &old_regs->r30, &old_unat);
>-	copy_reg(&bank[31-16], ms->pmsa_nat_bits, &old_regs->r31, &old_unat);
>+	restore_regs(old_regs, ms, &old_unat);
> 
> 	/* Next stack a struct switch_stack.  mca_asm.S built a partial
> 	 * switch_stack, copy it and fill in the blanks using pt_regs and
>@@ -1141,6 +1149,7 @@ ia64_mca_modify_original_stack(struct pt
> no_mod:
> 	mprintk(KERN_INFO "cpu %d, %s %s, original stack not modified\n",
> 			smp_processor_id(), type, msg);
>+	restore_regs(regs, ms, &old_unat);

old_unat is undefined here.  You need

  old_unat = regs->ar_unat;

> 	return previous_current;
> }

The rest of it looks good.