powerpc/perf: Fix setting of "to" addresses for BHRB

Currently we only set the "to" address in the branch stack when the CPU
explicitly gives us a value.  Unfortunately it only does this for XL form
branches (eg blr, bctr, bctar) and not I and B form branches (eg b, bc).

Fortunately if we read the instruction from memory we can extract the offset of
a branch and calculate the target address.

This adds a function power_pmu_bhrb_to() to calculate the target/to address of
the corresponding I and B form branches.  It handles branches in both user and
kernel spaces.  It also plumbs this into the perf brhb reading code.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 30 insertions, 1 deletions

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 3fdfe4575b8f..426180b84978 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -13,11 +13,13 @@
 #include <linux/perf_event.h>
 #include <linux/percpu.h>
 #include <linux/hardirq.h>
+#include <linux/uaccess.h>
 #include <asm/reg.h>
 #include <asm/pmc.h>
 #include <asm/machdep.h>
 #include <asm/firmware.h>
 #include <asm/ptrace.h>
+#include <asm/code-patching.h>
 
 #define BHRB_MAX_ENTRIES        32
 #define BHRB_TARGET             0x0000000000000002
@@ -362,6 +364,32 @@ void power_pmu_flush_branch_stack(void)
         if (ppmu->bhrb_nr)
                 power_pmu_bhrb_reset();
 }
+/* Calculate the to address for a branch */
+static __u64 power_pmu_bhrb_to(u64 addr)
+{
+        unsigned int instr;
+        int ret;
+        __u64 target;
+
+        if (is_kernel_addr(addr))
+                return branch_target((unsigned int *)addr);
+
+        /* Userspace: need copy instruction here then translate it */
+        pagefault_disable();
+        ret = __get_user_inatomic(instr, (unsigned int __user *)addr);
+        if (ret) {
+                pagefault_enable();
+                return 0;
+        }
+        pagefault_enable();
+
+        target = branch_target(&instr);
+        if ((!target) || (instr & BRANCH_ABSOLUTE))
+                return target;
+
+        /* Translate relative branch target from kernel to user address */
+        return target - (unsigned long)&instr + addr;
+}
 
 /* Processing BHRB entries */
 void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw)
@@ -426,7 +454,8 @@ void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw)
                                 /* Branches to immediate field 
                                    (ie I or B form) */
                                 cpuhw->bhrb_entries[u_index].from = addr;
-                                cpuhw->bhrb_entries[u_index].to = 0;
+                                cpuhw->bhrb_entries[u_index].to =
+                                        power_pmu_bhrb_to(addr);
                                 cpuhw->bhrb_entries[u_index].mispred = pred;
                                 cpuhw->bhrb_entries[u_index].predicted = ~pred;
                         }