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Peter Anvin" , Andrii Nakryiko , Song Liu , Ravi Bangoria , Ananth Narayan References: <21b52422864cea9f768ddee6be48102954cef984.1792064123.git.sandipan.das@amd.com> Content-Language: en-US From: "Mi, Dapeng" In-Reply-To: <21b52422864cea9f768ddee6be48102954cef984.1792064123.git.sandipan.das@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit LGTM. Thanks. Reviewed-by: Dapeng Mi On 10/15/2026 7:46 PM, Sandipan Das wrote: > The branch snapshot callback used by bpf_get_branch_snapshot() copies > up to x86_pmu.lbr_nr entries from cpuc->lbr_entries[], even when the > last LBR read kept fewer branches. The entries past lbr_stack.nr are > invalid, but they end up reaching BPF programs. > > Limit copying to lbr_stack.nr entries and also reset lbr_stack.nr when > amd_pmu_lbr_read() skips reading the registers, so that a stale count > is never reused. > > Fixes: a4d18112e531 ("perf/x86/amd: Support capturing LBR from software events") > Reported-by: Sashiko > Closes: https://lore.kernel.org/all/sashiko-outbox-163130@kernel.org/ > Signed-off-by: Sandipan Das > --- > arch/x86/events/amd/core.c | 2 +- > arch/x86/events/amd/lbr.c | 4 +++- > 2 files changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c > index 49b6b8fce566..bf631f60757c 100644 > --- a/arch/x86/events/amd/core.c > +++ b/arch/x86/events/amd/core.c > @@ -944,7 +944,7 @@ static int amd_pmu_v2_snapshot_branch_stack(struct perf_branch_entry *entries, u > cpuc = this_cpu_ptr(&cpu_hw_events); > > amd_pmu_lbr_read(); > - cnt = min(cnt, x86_pmu.lbr_nr); > + cnt = min(cnt, cpuc->lbr_stack.nr); > memcpy(entries, cpuc->lbr_entries, sizeof(struct perf_branch_entry) * cnt); > > amd_pmu_v2_enable_all(0); > diff --git a/arch/x86/events/amd/lbr.c b/arch/x86/events/amd/lbr.c > index 1e1b2f08cb51..a00d3850c4a8 100644 > --- a/arch/x86/events/amd/lbr.c > +++ b/arch/x86/events/amd/lbr.c > @@ -165,8 +165,10 @@ void amd_pmu_lbr_read(void) > struct branch_entry entry; > int out = 0, idx, i; > > - if (!cpuc->lbr_users) > + if (!cpuc->lbr_users) { > + cpuc->lbr_stack.nr = 0; > return; > + } > > for (i = 0; i < x86_pmu.lbr_nr; i++) { > entry.from.full = amd_pmu_lbr_get_from(i);