This is a note to let you know that I've just added the patch titled
perf/x86/amd/lbr: Discard erroneous branch entries
to the 6.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
perf-x86-amd-lbr-discard-erroneous-branch-entries.patch
and it can be found in the queue-6.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 42e0501037d90654302fe74c07b413b78760dfeb
Author: Sandipan Das <sandipan.das@xxxxxxx>
Date: Mon Jan 29 16:36:25 2024 +0530
perf/x86/amd/lbr: Discard erroneous branch entries
[ Upstream commit 29297ffffb0bf388778bd4b581a43cee6929ae65 ]
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 <sandipan.das@xxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: https://bugzilla.kernel.org/attachment.cgi?id=305518
Link: https://lore.kernel.org/r/3ad2aa305f7396d41a40e3f054f740d464b16b7f.1706526029.git.sandipan.das@xxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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);
