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authorScott Wood <scottwood@freescale.com>2013-05-13 14:14:53 +0000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2013-05-14 16:00:19 +1000
commit6cecf76b47ba6bea3c81d170afc2e0b244e5849c (patch)
treeff2d8e3516815071e4b46d56673699a5224fd9ed /arch
parentdcb615aef988b57deef3d9b4557ff20f681a82b0 (diff)
powerpc/booke64: Fix kernel hangs at kernel_dbg_exc
MSR_DE is not cleared on entry to the kernel, and we don't clear it explicitly outside of debug code. If we have MSR_DE set in prime_debug_regs(), and the new thread has events enabled in DBCR0 (e.g. ICMP is set in thread->dbsr0, even though it was cleared in the real DBCR0 when the thread got scheduled out), we'll end up taking a debug exception in the kernel when DBCR0 is loaded. DSRR0 will not point to an exception vector, and the kernel ends up hanging at kernel_dbg_exc. Fix this by always clearing MSR_DE when we load new debug state. Another observed source of kernel_dbg_exc hangs is with the branch taken event. If this event is active, but we take a non-debug trap (e.g. a TLB miss or an asynchronous interrupt) before the next branch. We end up taking a branch-taken debug exception on the initial branch instruction of the exception vector, but because the debug exception is DBSR_BT rather than DBSR_IC we branch to kernel_dbg_exc before even checking the DSRR0 address. Fix this by checking for DBSR_BT as well as DBSR_IC, which is what 32-bit does and what the comments suggest was intended in the 64-bit code as well. Signed-off-by: Scott Wood <scottwood@freescale.com> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/powerpc/kernel/exceptions-64e.S8
-rw-r--r--arch/powerpc/kernel/process.c7
2 files changed, 11 insertions, 4 deletions
diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
index 42a756eec9ff..645170a07ada 100644
--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S
@@ -489,7 +489,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
*/
mfspr r14,SPRN_DBSR /* check single-step/branch taken */
- andis. r15,r14,DBSR_IC@h
+ andis. r15,r14,(DBSR_IC|DBSR_BT)@h
beq+ 1f
LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e)
@@ -500,7 +500,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
bge+ cr1,1f
/* here it looks like we got an inappropriate debug exception. */
- lis r14,DBSR_IC@h /* clear the IC event */
+ lis r14,(DBSR_IC|DBSR_BT)@h /* clear the event */
rlwinm r11,r11,0,~MSR_DE /* clear DE in the CSRR1 value */
mtspr SPRN_DBSR,r14
mtspr SPRN_CSRR1,r11
@@ -555,7 +555,7 @@ kernel_dbg_exc:
*/
mfspr r14,SPRN_DBSR /* check single-step/branch taken */
- andis. r15,r14,DBSR_IC@h
+ andis. r15,r14,(DBSR_IC|DBSR_BT)@h
beq+ 1f
LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e)
@@ -566,7 +566,7 @@ kernel_dbg_exc:
bge+ cr1,1f
/* here it looks like we got an inappropriate debug exception. */
- lis r14,DBSR_IC@h /* clear the IC event */
+ lis r14,(DBSR_IC|DBSR_BT)@h /* clear the event */
rlwinm r11,r11,0,~MSR_DE /* clear DE in the DSRR1 value */
mtspr SPRN_DBSR,r14
mtspr SPRN_DSRR1,r11
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 21981a89e394..a902723fdc69 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -339,6 +339,13 @@ static void set_debug_reg_defaults(struct thread_struct *thread)
static void prime_debug_regs(struct thread_struct *thread)
{
+ /*
+ * We could have inherited MSR_DE from userspace, since
+ * it doesn't get cleared on exception entry. Make sure
+ * MSR_DE is clear before we enable any debug events.
+ */
+ mtmsr(mfmsr() & ~MSR_DE);
+
mtspr(SPRN_IAC1, thread->iac1);
mtspr(SPRN_IAC2, thread->iac2);
#if CONFIG_PPC_ADV_DEBUG_IACS > 2