[Patch v4 0/5] perf/x86: Limit branch snapshots to valid entries

[Dapeng Mi <dapeng1.mi@linux.intel.com>]

Sashiko reported that the vendor-specific branch snapshot callbacks
used by bpf_get_branch_snapshot() copy up to x86_pmu.lbr_nr entries
from cpuc->lbr_entries[], regardless of how many valid entries the
last LBR read produced. This makes BPF programs read stale or invalid
branch records. Patch 1 addresses AMD and patch 2 addresses Intel.

Changes in v4:
- Patch 01: Disable LBR if parsed x86_pmu.lbr_nr exceeds
  MAX_LBR_ENTRIES (Sashiko).
- Patch 05: New patch, which always snapshots live hardware LBR stack
  for BPF path (Sashiko).

Changes in v3:
- Patch 01: A new patch to ensure x86_pmu.lbr_nr not to exclude
  MAX_LBR_ENTRIES (Internal Sashiko).
- Patch 03: Clean cached LBR stack when reseting hardware LBR registers,
  which prevents stale LBR stack leakage.
- Patch 04: Don't reset cached LBR stack if all LBR events are PEBS
  events. This ensures PEBS captured LBR stack isn't cleared (Sashiko).

Changes in v2:
- Include a fix for Intel LBR.
- Add Tested-by from Dapeng to the Intel fix.
  https://lore.kernel.org/all/eb6c7bda-0dcf-4fac-ad69-9f5b24abc21b@linux.intel.com/

History:
v3: https://lore.kernel.org/all/20261019070836.2972403-1-dapeng1.mi@linux.intel.com/
v2: https://lore.kernel.org/all/cover.1792064123.git.sandipan.das@amd.com/
v1: https://lore.kernel.org/all/20261007181002.4005262-1-sandipan.das@amd.com/

Dapeng Mi (4):
  perf/x86: Disable LBR if x86_pmu.lbr_nr exceeds MAX_LBR_ENTRIES
  perf/x86/intel/lbr: Reset the cached LBR stack in
    intel_pmu_lbr_reset()
  perf/x86/intel/lbr: Limit branch snapshots to valid entries
  pef/x86/intel: Always snapshot live hardware LBR state for BPF path

Sandipan Das (1):
  perf/x86/amd/lbr: Limit branch snapshots to valid entries

 arch/x86/events/amd/core.c   |  2 +-
 arch/x86/events/amd/lbr.c    |  4 +++-
 arch/x86/events/core.c       |  6 +++++
 arch/x86/events/intel/core.c | 45 +++++++++++++++++++++++++++++++++---
 arch/x86/events/intel/lbr.c  | 19 +++++++--------
 5 files changed, 62 insertions(+), 14 deletions(-)


base-commit: f5a78ecccd98a04c47cea1cd63c2a2fdce8a4b48
-- 
2.34.1