queue-6.8/perf-x86-amd-lbr-discard-erroneous-branch-entries.patch

   1 From 42e0501037d90654302fe74c07b413b78760dfeb Mon Sep 17 00:00:00 2001
   2 From: Sasha Levin <sashal@kernel.org>
   3 Date: Mon, 29 Jan 2024 16:36:25 +0530
   4 Subject: perf/x86/amd/lbr: Discard erroneous branch entries
   5
   6 From: Sandipan Das <sandipan.das@amd.com>
   7
   8 [ Upstream commit 29297ffffb0bf388778bd4b581a43cee6929ae65 ]
   9
  10 The Revision Guide for AMD Family 19h Model 10-1Fh processors declares
  11 Erratum 1452 which states that non-branch entries may erroneously be
  12 recorded in the Last Branch Record (LBR) stack with the valid and
  13 spec bits set.
  14
  15 Such entries can be recognized by inspecting bit 61 of the corresponding
  16 LastBranchStackToIp register. This bit is currently reserved but if found
  17 to be set, the associated branch entry should be discarded.
  18
  19 Signed-off-by: Sandipan Das <sandipan.das@amd.com>
  20 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  21 Cc: Peter Zijlstra <peterz@infradead.org>
  22 Link: https://bugzilla.kernel.org/attachment.cgi?id=305518
  23 Link: https://lore.kernel.org/r/3ad2aa305f7396d41a40e3f054f740d464b16b7f.1706526029.git.sandipan.das@amd.com
  24 Signed-off-by: Sasha Levin <sashal@kernel.org>
  25 ---
  26  arch/x86/events/amd/lbr.c | 6 ++++--
  27  1 file changed, 4 insertions(+), 2 deletions(-)
  28
  29 diff --git a/arch/x86/events/amd/lbr.c b/arch/x86/events/amd/lbr.c
  30 index eb31f850841a8..4a1e600314d5d 100644
  31 --- a/arch/x86/events/amd/lbr.c
  32 +++ b/arch/x86/events/amd/lbr.c
  33 @@ -173,9 +173,11 @@ void amd_pmu_lbr_read(void)
  34
  35                 /*
  36                  * Check if a branch has been logged; if valid = 0, spec = 0
  37 -                * then no branch was recorded
  38 +                * then no branch was recorded; if reserved = 1 then an
  39 +                * erroneous branch was recorded (see Erratum 1452)
  40                  */
  41 -               if (!entry.to.split.valid && !entry.to.split.spec)
  42 +               if ((!entry.to.split.valid && !entry.to.split.spec) ||
  43 +                   entry.to.split.reserved)
  44                         continue;
  45
  46                 perf_clear_branch_entry_bitfields(br + out);
  47 --
  48 2.43.0
  49