diff options
| author | Scott Wood <scottwood@freescale.com> | 2013-05-13 14:14:53 +0000 |
|---|---|---|
| committer | Benjamin Herrenschmidt <benh@kernel.crashing.org> | 2013-05-14 16:00:19 +1000 |
| commit | 6cecf76b47ba6bea3c81d170afc2e0b244e5849c (patch) | |
| tree | ff2d8e3516815071e4b46d56673699a5224fd9ed /arch | |
| parent | dcb615aef988b57deef3d9b4557ff20f681a82b0 (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.S | 8 | ||||
| -rw-r--r-- | arch/powerpc/kernel/process.c | 7 |
2 files changed, 11 insertions, 4 deletions
diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S index 42a756eec9f..645170a07ad 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 21981a89e39..a902723fdc6 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 |