powerpc, hw_breakpoint: Discard extraneous interrupt due to accesses outside symbol...

Many a times, the requested breakpoint length can be less than the
fixed breakpoint length i.e. 8 bytes supported by PowerPC 64-bit
server (Book III S) processors.  This could lead to extraneous
interrupts resulting in false breakpoint notifications.  This
detects and discards such interrupts for non-ptrace requests.
We don't change ptrace behaviour to avoid breaking compatability.

[Suggestion from Paul Mackerras <paulus@samba.org> to add a new flag in
'struct arch_hw_breakpoint' to identify extraneous interrupts]

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

diff --git a/arch/powerpc/include/asm/hw_breakpoint.h b/arch/powerpc/include/asm/hw_breakpoint.h
index 6576bad1069c0d6ada17a99b97ed988f53696d8b..ea87f8ae7bdbe98163758743258404393c04ad8b 100644 (file)
--- a/arch/powerpc/include/asm/hw_breakpoint.h
+++ b/arch/powerpc/include/asm/hw_breakpoint.h
@@ -27,6 +27,7 @@
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
 
 struct arch_hw_breakpoint {
+       bool            extraneous_interrupt;
        u8              len; /* length of the target data symbol */
        int             type;
        unsigned long   address;

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index 7bd01a56d1944959e1acc9d3868a3bcdf17fdfaf..ed39805a3b84ee2f6300b95c48b0459d7079e991 100644 (file)
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -204,6 +204,7 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
        int stepped = 1;
        struct arch_hw_breakpoint *info;
        unsigned int instr;
+       unsigned long dar = regs->dar;
 
        /* Disable breakpoints during exception handling */
        set_dabr(0);
@@ -234,6 +235,22 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
                goto out;
        }
 
+       /*
+        * Verify if dar lies within the address range occupied by the symbol
+        * being watched to filter extraneous exceptions.
+        */
+       if (!((bp->attr.bp_addr <= dar) &&
+            (dar <= (bp->attr.bp_addr + bp->attr.bp_len)))) {
+               /*
+                * This exception is triggered not because of a memory access
+                * on the monitored variable but in the double-word address
+                * range in which it is contained. We will consume this
+                * exception, considering it as 'noise'.
+                */
+               info->extraneous_interrupt = true;
+       } else
+               info->extraneous_interrupt = false;
+
        /* Do not emulate user-space instructions, instead single-step them */
        if (user_mode(regs)) {
                bp->ctx->task->thread.last_hit_ubp = bp;
@@ -261,7 +278,8 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
         * As a policy, the callback is invoked in a 'trigger-after-execute'
         * fashion
         */
-       perf_bp_event(bp, regs);
+       if (!info->extraneous_interrupt)
+               perf_bp_event(bp, regs);
 
        set_dabr(info->address | info->type | DABR_TRANSLATION);
 out:
@@ -292,7 +310,8 @@ int __kprobes single_step_dabr_instruction(struct die_args *args)
         * We shall invoke the user-defined callback function in the single
         * stepping handler to confirm to 'trigger-after-execute' semantics
         */
-       perf_bp_event(bp, regs);
+       if (!bp_info->extraneous_interrupt)
+               perf_bp_event(bp, regs);
 
        /*
         * Do not disable MSR_SE if the process was already in