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Subject[PATCH 04/72] Blackfin: make EVT3->EVT5 lowering more robust wrt IPEND[4]
Date
From: Robin Getz <robin.getz@analog.com>

We handle many exceptions at EVT5 (hardware error level) so that we can
catch exceptions in our exception handling code. Today - if the global
interrupt enable bit (IPEND[4]) is set (interrupts disabled) our trap
handling code goes into a infinite loop, since we need interrupts to be
on to defer things to EVT5.

Normal kernel code should not trigger this for any reason as IPEND[4] gets
cleared early (when doing an interrupt context save) and the kernel stack
there should be sane (or something much worse is happening in the system).
But there have been a few times where this has happened, so this change
makes sure we dump a proper crash message even when things have gone south.

Signed-off-by: Robin Getz <robin.getz@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
---
arch/blackfin/include/asm/pda.h | 1 +
arch/blackfin/kernel/asm-offsets.c | 1 +
arch/blackfin/kernel/traps.c | 19 ++++----
arch/blackfin/mach-common/entry.S | 86 ++++++++++++++++++++++-------------
4 files changed, 66 insertions(+), 41 deletions(-)
diff --git a/arch/blackfin/include/asm/pda.h b/arch/blackfin/include/asm/pda.h
index b42555c..69b96b4 100644
--- a/arch/blackfin/include/asm/pda.h
+++ b/arch/blackfin/include/asm/pda.h
@@ -50,6 +50,7 @@ struct blackfin_pda { /* Per-processor Data Area */
unsigned long ex_optr;
unsigned long ex_buf[4];
unsigned long ex_imask; /* Saved imask from exception */
+ unsigned long ex_ipend; /* Saved IPEND from exception */
unsigned long *ex_stack; /* Exception stack space */

#ifdef ANOMALY_05000261
diff --git a/arch/blackfin/kernel/asm-offsets.c b/arch/blackfin/kernel/asm-offsets.c
index b5df945..8ad4f2c 100644
--- a/arch/blackfin/kernel/asm-offsets.c
+++ b/arch/blackfin/kernel/asm-offsets.c
@@ -145,6 +145,7 @@ int main(void)
DEFINE(PDA_EXBUF, offsetof(struct blackfin_pda, ex_buf));
DEFINE(PDA_EXIMASK, offsetof(struct blackfin_pda, ex_imask));
DEFINE(PDA_EXSTACK, offsetof(struct blackfin_pda, ex_stack));
+ DEFINE(PDA_EXIPEND, offsetof(struct blackfin_pda, ex_ipend));
#ifdef ANOMALY_05000261
DEFINE(PDA_LFRETX, offsetof(struct blackfin_pda, last_cplb_fault_retx));
#endif
diff --git a/arch/blackfin/kernel/traps.c b/arch/blackfin/kernel/traps.c
index bf2b2d1..fccf741 100644
--- a/arch/blackfin/kernel/traps.c
+++ b/arch/blackfin/kernel/traps.c
@@ -267,11 +267,6 @@ asmlinkage void trap_c(struct pt_regs *fp)
* double faults if the stack has become corrupt
*/

-#ifndef CONFIG_KGDB
- /* IPEND is skipped if KGDB isn't enabled (see entry code) */
- fp->ipend = bfin_read_IPEND();
-#endif
-
/* trap_c() will be called for exceptions. During exceptions
* processing, the pc value should be set with retx value.
* With this change we can cleanup some code in signal.c- TODO
@@ -1116,10 +1111,16 @@ void show_regs(struct pt_regs *fp)

verbose_printk(KERN_NOTICE "%s", linux_banner);

- verbose_printk(KERN_NOTICE "\nSEQUENCER STATUS:\t\t%s\n",
- print_tainted());
- verbose_printk(KERN_NOTICE " SEQSTAT: %08lx IPEND: %04lx SYSCFG: %04lx\n",
- (long)fp->seqstat, fp->ipend, fp->syscfg);
+ verbose_printk(KERN_NOTICE "\nSEQUENCER STATUS:\t\t%s\n", print_tainted());
+ verbose_printk(KERN_NOTICE " SEQSTAT: %08lx IPEND: %04lx IMASK: %04lx SYSCFG: %04lx\n",
+ (long)fp->seqstat, fp->ipend, cpu_pda[smp_processor_id()].ex_imask, fp->syscfg);
+ if (fp->ipend & EVT_IRPTEN)
+ verbose_printk(KERN_NOTICE " Global Interrupts Disabled (IPEND[4])\n");
+ if (!(cpu_pda[smp_processor_id()].ex_imask & (EVT_IVG13 | EVT_IVG12 | EVT_IVG11 |
+ EVT_IVG10 | EVT_IVG9 | EVT_IVG8 | EVT_IVG7 | EVT_IVTMR)))
+ verbose_printk(KERN_NOTICE " Peripheral interrupts masked off\n");
+ if (!(cpu_pda[smp_processor_id()].ex_imask & (EVT_IVG15 | EVT_IVG14)))
+ verbose_printk(KERN_NOTICE " Kernel interrupts masked off\n");
if ((fp->seqstat & SEQSTAT_EXCAUSE) == VEC_HWERR) {
verbose_printk(KERN_NOTICE " HWERRCAUSE: 0x%lx\n",
(fp->seqstat & SEQSTAT_HWERRCAUSE) >> 14);
diff --git a/arch/blackfin/mach-common/entry.S b/arch/blackfin/mach-common/entry.S
index fb1795d..4c07fcb 100644
--- a/arch/blackfin/mach-common/entry.S
+++ b/arch/blackfin/mach-common/entry.S
@@ -301,25 +301,31 @@ ENTRY(_ex_replaceable)
nop;

ENTRY(_ex_trap_c)
+ /* The only thing that has been saved in this context is
+ * (R7:6,P5:4), ASTAT & SP - don't use anything else
+ */
+
+ GET_PDA(p5, r6);
+
/* Make sure we are not in a double fault */
p4.l = lo(IPEND);
p4.h = hi(IPEND);
r7 = [p4];
CC = BITTST (r7, 5);
if CC jump _double_fault;
+ [p5 + PDA_EXIPEND] = r7;

/* Call C code (trap_c) to handle the exception, which most
* likely involves sending a signal to the current process.
* To avoid double faults, lower our priority to IRQ5 first.
*/
- P5.h = _exception_to_level5;
- P5.l = _exception_to_level5;
+ r7.h = _exception_to_level5;
+ r7.l = _exception_to_level5;
p4.l = lo(EVT5);
p4.h = hi(EVT5);
- [p4] = p5;
+ [p4] = r7;
csync;

- GET_PDA(p5, r6);
#ifndef CONFIG_DEBUG_DOUBLEFAULT

/*
@@ -349,8 +355,7 @@ ENTRY(_ex_trap_c)
BITCLR(r6, SYSCFG_SSSTEP_P);
SYSCFG = r6;

- /* Disable all interrupts, but make sure level 5 is enabled so
- * we can switch to that level. Save the old mask. */
+ /* Save the current IMASK, since we change in order to jump to level 5 */
cli r6;
[p5 + PDA_EXIMASK] = r6;

@@ -358,9 +363,21 @@ ENTRY(_ex_trap_c)
p4.h = hi(SAFE_USER_INSTRUCTION);
retx = p4;

+ /* Disable all interrupts, but make sure level 5 is enabled so
+ * we can switch to that level.
+ */
r6 = 0x3f;
sti r6;

+ /* In case interrupts are disabled IPEND[4] (global interrupt disable bit)
+ * clear it (re-enabling interrupts again) by the special sequence of pushing
+ * RETI onto the stack. This way we can lower ourselves to IVG5 even if the
+ * exception was taken after the interrupt handler was called but before it
+ * got a chance to enable global interrupts itself.
+ */
+ [--sp] = reti;
+ sp += 4;
+
raise 5;
jump.s _bfin_return_from_exception;
ENDPROC(_ex_trap_c)
@@ -420,47 +437,52 @@ ENDPROC(_double_fault)
ENTRY(_exception_to_level5)
SAVE_ALL_SYS

- GET_PDA(p4, r7); /* Fetch current PDA */
- r6 = [p4 + PDA_RETX];
+ GET_PDA(p5, r7); /* Fetch current PDA */
+ r6 = [p5 + PDA_RETX];
[sp + PT_PC] = r6;

- r6 = [p4 + PDA_SYSCFG];
+ r6 = [p5 + PDA_SYSCFG];
[sp + PT_SYSCFG] = r6;

- /* Restore interrupt mask. We haven't pushed RETI, so this
- * doesn't enable interrupts until we return from this handler. */
- r6 = [p4 + PDA_EXIMASK];
- sti r6;
-
/* Restore the hardware error vector. */
- P5.h = _evt_ivhw;
- P5.l = _evt_ivhw;
+ r7.h = _evt_ivhw;
+ r7.l = _evt_ivhw;
p4.l = lo(EVT5);
p4.h = hi(EVT5);
- [p4] = p5;
+ [p4] = r7;
csync;

- p2.l = lo(IPEND);
- p2.h = hi(IPEND);
- csync;
- r0 = [p2]; /* Read current IPEND */
- [sp + PT_IPEND] = r0; /* Store IPEND */
+#ifdef CONFIG_DEBUG_DOUBLEFAULT
+ /* Now that we have the hardware error vector programmed properly
+ * we can re-enable interrupts (IPEND[4]), so if the _trap_c causes
+ * another hardware error, we can catch it (self-nesting).
+ */
+ [--sp] = reti;
+ sp += 4;
+#endif
+
+ r7 = [p5 + PDA_EXIPEND] /* Read the IPEND from the Exception state */
+ [sp + PT_IPEND] = r7; /* Store IPEND onto the stack */

r0 = sp; /* stack frame pt_regs pointer argument ==> r0 */
SP += -12;
call _trap_c;
SP += 12;

-#ifdef CONFIG_DEBUG_DOUBLEFAULT
- /* Grab ILAT */
- p2.l = lo(ILAT);
- p2.h = hi(ILAT);
- r0 = [p2];
- r1 = 0x20; /* Did I just cause anther HW error? */
- r0 = r0 & r1;
- CC = R0 == R1;
- if CC JUMP _double_fault;
-#endif
+ /* If interrupts were off during the exception (IPEND[4] = 1), turn them off
+ * before we return.
+ */
+ CC = BITTST(r7, EVT_IRPTEN_P)
+ if !CC jump 1f;
+ /* this will load a random value into the reti register - but that is OK,
+ * since we do restore it to the correct value in the 'RESTORE_ALL_SYS' macro
+ */
+ sp += -4;
+ reti = [sp++];
+1:
+ /* restore the interrupt mask (IMASK) */
+ r6 = [p5 + PDA_EXIMASK];
+ sti r6;

call _ret_from_exception;
RESTORE_ALL_SYS
--
1.6.4.2


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