perf/x86/amd/lbr: Add LbrExtV2 branch speculation info support

Provide branch speculation information captured via AMD Last Branch Record
Extension Version 2 (LbrExtV2) by setting the speculation info in branch
records. The info is based on the "valid" and "spec" bits in the Branch To
registers.

Suggested-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Sandipan Das <sandipan.das@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/ddc02f6320464cad0e3ff5bdb2314531568a91bc.1660211399.git.sandipan.das@amd.com

diff --git a/arch/x86/events/amd/lbr.c b/arch/x86/events/amd/lbr.c
index eb84f19..2e1c157 100644 (file)
--- a/arch/x86/events/amd/lbr.c
+++ b/arch/x86/events/amd/lbr.c
@@ -146,12 +146,19 @@ static void amd_pmu_lbr_filter(void)
        }
 }
 
+static const int lbr_spec_map[PERF_BR_SPEC_MAX] = {
+       PERF_BR_SPEC_NA,
+       PERF_BR_SPEC_WRONG_PATH,
+       PERF_BR_NON_SPEC_CORRECT_PATH,
+       PERF_BR_SPEC_CORRECT_PATH,
+};
+
 void amd_pmu_lbr_read(void)
 {
        struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
        struct perf_branch_entry *br = cpuc->lbr_entries;
        struct branch_entry entry;
-       int out = 0, i;
+       int out = 0, idx, i;
 
        if (!cpuc->lbr_users)
                return;
@@ -160,8 +167,11 @@ void amd_pmu_lbr_read(void)
                entry.from.full = amd_pmu_lbr_get_from(i);
                entry.to.full   = amd_pmu_lbr_get_to(i);
 
-               /* Check if a branch has been logged */
-               if (!entry.to.split.valid)
+               /*
+                * Check if a branch has been logged; if valid = 0, spec = 0
+                * then no branch was recorded
+                */
+               if (!entry.to.split.valid && !entry.to.split.spec)
                        continue;
 
                perf_clear_branch_entry_bitfields(br + out);
@@ -170,6 +180,25 @@ void amd_pmu_lbr_read(void)
                br[out].to      = sign_ext_branch_ip(entry.to.split.ip);
                br[out].mispred = entry.from.split.mispredict;
                br[out].predicted = !br[out].mispred;
+
+               /*
+                * Set branch speculation information using the status of
+                * the valid and spec bits.
+                *
+                * When valid = 0, spec = 0, no branch was recorded and the
+                * entry is discarded as seen above.
+                *
+                * When valid = 0, spec = 1, the recorded branch was
+                * speculative but took the wrong path.
+                *
+                * When valid = 1, spec = 0, the recorded branch was
+                * non-speculative but took the correct path.
+                *
+                * When valid = 1, spec = 1, the recorded branch was
+                * speculative and took the correct path
+                */
+               idx = (entry.to.split.valid << 1) | entry.to.split.spec;
+               br[out].spec = lbr_spec_map[idx];
                out++;
        }