5.4-stable review patch. If anyone has any objections, please let me know.
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From: Dapeng Mi dapeng1.mi@linux.intel.com
commit 71dcc11c2cd9e434c34a63154ecadca21c135ddd upstream.
Currently when a user samples user space GPRs (--user-regs option) with PEBS, the user space GPRs actually always come from software PMI instead of from PEBS hardware. This leads to the sampled GPRs to possibly be inaccurate for single PEBS record case because of the skid between counter overflow and GPRs sampling on PMI.
For the large PEBS case, it is even worse. If user sets the exclude_kernel attribute, large PEBS would be used to sample user space GPRs, but since PEBS GPRs group is not really enabled, it leads to all samples in the large PEBS record to share the same piece of user space GPRs, like this reproducer shows:
$ perf record -e branches:pu --user-regs=ip,ax -c 100000 ./foo $ perf report -D | grep "AX"
.... AX 0x000000003a0d4ead .... AX 0x000000003a0d4ead .... AX 0x000000003a0d4ead .... AX 0x000000003a0d4ead .... AX 0x000000003a0d4ead .... AX 0x000000003a0d4ead .... AX 0x000000003a0d4ead .... AX 0x000000003a0d4ead .... AX 0x000000003a0d4ead .... AX 0x000000003a0d4ead .... AX 0x000000003a0d4ead
So enable GPRs group for user space GPRs sampling and prioritize reading GPRs from PEBS. If the PEBS sampled GPRs is not user space GPRs (single PEBS record case), perf_sample_regs_user() modifies them to user space GPRs.
[ mingo: Clarified the changelog. ]
Fixes: c22497f5838c ("perf/x86/intel: Support adaptive PEBS v4") Signed-off-by: Dapeng Mi dapeng1.mi@linux.intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Ingo Molnar mingo@kernel.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20250415104135.318169-2-dapeng1.mi@linux.intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/events/intel/ds.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
--- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -985,8 +985,10 @@ static u64 pebs_update_adaptive_cfg(stru * + precise_ip < 2 for the non event IP * + For RTM TSX weight we need GPRs for the abort code. */ - gprs = (sample_type & PERF_SAMPLE_REGS_INTR) && - (attr->sample_regs_intr & PEBS_GP_REGS); + gprs = ((sample_type & PERF_SAMPLE_REGS_INTR) && + (attr->sample_regs_intr & PEBS_GP_REGS)) || + ((sample_type & PERF_SAMPLE_REGS_USER) && + (attr->sample_regs_user & PEBS_GP_REGS));
tsx_weight = (sample_type & PERF_SAMPLE_WEIGHT) && ((attr->config & INTEL_ARCH_EVENT_MASK) == @@ -1569,7 +1571,7 @@ static void setup_pebs_adaptive_sample_d regs->flags &= ~PERF_EFLAGS_EXACT; }
- if (sample_type & PERF_SAMPLE_REGS_INTR) + if (sample_type & (PERF_SAMPLE_REGS_INTR | PERF_SAMPLE_REGS_USER)) adaptive_pebs_save_regs(regs, gprs); }