Re: powerpc/fsl_book3e: fix the relocatable bug in debug interrupt handler

On Mon, 2015-08-10 at 10:23 +0800, Huang, Yuanjie wrote:

Hi Scott,

On 08/08/2015 10:29 AM, Scott Wood wrote:

quoted

[Please wrap commit messages at around 74 columns]

Ok, I will when sending a new version.

quoted

On Fri, Aug 07, 2015 at 02:58:10PM +0800, Yuanjie Huang wrote:

quoted

PowerPC Book3E processor features hardware-supported single instruction
execution, and it is used for ptrace(PTRACE_SINGLESTEP, ...).  When a
debugger loads a debuggee, it typically sets the CPU to yield debug
interrupt on first instruction complete or branch taken.  However, the
newly-forked child process could run into instruction TLB miss
exception handler when switched to, and causes a debug interrupt in the
exception entry sequence.  This is not expected by caller of
ptrace(PTRACE_SINGLESTEP, ...), so the next instruction address saved
in DSRR0 is checked against the boundary of exception entry sequence,
to ensure the kernel only process the interrupt as a normal exception
if the address does not fall in the exception entry sequence.  Failure
in obtaining the correct boundary leads to such debug exception handled
as from privileged mode, and causes kernel oops.

The LOAD_REG_IMMEDIATE can't be used to load the boundary addresses
when relocatable enabled, so this patch replace them with
LOAD_REG_ADDR_PIC.  LR is backed up and restored before and after
calling LOAD_REG_ADDR_PIC, because LOAD_REG_ADDR_PIC clobbers it.

Signed-off-by: Yuanjie Huang <redacted>
---
  arch/powerpc/kernel/exceptions-64e.S | 24 ++++++++++++++++++++++++
  1 file changed, 24 insertions(+)

diff --git a/arch/powerpc/kernel/exceptions-64e.S 

b/arch/powerpc/kernel/exceptions-64e.S
index 3e68d1c..c475f569 100644

--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S

@@ -735,12 +735,24 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
          andis.  r15,r14,(DBSR_IC|DBSR_BT)@h
          beq+    1f
  
+#ifdef CONFIG_RELOCATABLE
+ mflr    r14
+ LOAD_REG_ADDR_PIC(r15,interrupt_base_book3e)
+ mtlr    r14
+ cmpld   cr0,r10,r15
+ blt+    cr0,1f
+ LOAD_REG_ADDR_PIC(r15,interrupt_end_book3e)
+ mtlr    r14
+ cmpld   cr0,r10,r15
+ bge+    cr0,1f
+#else

CONFIG_RELOCATABLE is not supported on 64-bit book3e without applying
additional patches, such as the RFC patchset I posted recently that
contained the patch "powerpc/book3e-64: rename interrupt_end_book3e with
__end_interrupts".  But if you've applied that patchset, then you
wouldn't be working with the name interrupt_base_book3e, so how are you
seeing this?

Actually I have merged additional patches submitted but not merged to 
make CONFIG_RELOCATABLE work with 64-bit book3e. I am happy to delay 
this until those patches are merged, and sent an adjusted version. Shall 
I wait until they are merged?

Yes, or base the patch on top of them and cite the dependency below the --- 
line in the changelog.

-Scott