From: Sandipan Das Date: Mon, 29 Jan 2024 11:06:25 +0000 (+0530) Subject: perf/x86/amd/lbr: Discard erroneous branch entries X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=29297ffffb0bf388778bd4b581a43cee6929ae65;p=linux.git perf/x86/amd/lbr: Discard erroneous branch entries The Revision Guide for AMD Family 19h Model 10-1Fh processors declares Erratum 1452 which states that non-branch entries may erroneously be recorded in the Last Branch Record (LBR) stack with the valid and spec bits set. Such entries can be recognized by inspecting bit 61 of the corresponding LastBranchStackToIp register. This bit is currently reserved but if found to be set, the associated branch entry should be discarded. Signed-off-by: Sandipan Das Signed-off-by: Ingo Molnar Cc: Peter Zijlstra Link: https://bugzilla.kernel.org/attachment.cgi?id=305518 Link: https://lore.kernel.org/r/3ad2aa305f7396d41a40e3f054f740d464b16b7f.1706526029.git.sandipan.das@amd.com --- diff --git a/arch/x86/events/amd/lbr.c b/arch/x86/events/amd/lbr.c index eb31f850841a8..4a1e600314d5d 100644 --- a/arch/x86/events/amd/lbr.c +++ b/arch/x86/events/amd/lbr.c @@ -173,9 +173,11 @@ void amd_pmu_lbr_read(void) /* * Check if a branch has been logged; if valid = 0, spec = 0 - * then no branch was recorded + * then no branch was recorded; if reserved = 1 then an + * erroneous branch was recorded (see Erratum 1452) */ - if (!entry.to.split.valid && !entry.to.split.spec) + if ((!entry.to.split.valid && !entry.to.split.spec) || + entry.to.split.reserved) continue; perf_clear_branch_entry_bitfields(br + out);