This is a note to let you know that I've just added the patch titled
perf/x86/lbr: Enable the branch type for the Arch LBR by default
to the 5.10-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-lbr-enable-the-branch-type-for-the-arch-lbr-by-default.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 32ba156df1b1c8804a4e5be5339616945eafea22 Mon Sep 17 00:00:00 2001
From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Date: Tue, 16 Aug 2022 05:56:11 -0700
Subject: perf/x86/lbr: Enable the branch type for the Arch LBR by default
From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
commit 32ba156df1b1c8804a4e5be5339616945eafea22 upstream.
On the platform with Arch LBR, the HW raw branch type encoding may leak
to the perf tool when the SAVE_TYPE option is not set.
In the intel_pmu_store_lbr(), the HW raw branch type is stored in
lbr_entries[].type. If the SAVE_TYPE option is set, the
lbr_entries[].type will be converted into the generic PERF_BR_* type
in the intel_pmu_lbr_filter() and exposed to the user tools.
But if the SAVE_TYPE option is NOT set by the user, the current perf
kernel doesn't clear the field. The HW raw branch type leaks.
There are two solutions to fix the issue for the Arch LBR.
One is to clear the field if the SAVE_TYPE option is NOT set.
The other solution is to unconditionally convert the branch type and
expose the generic type to the user tools.
The latter is implemented here, because
- The branch type is valuable information. I don't see a case where
you would not benefit from the branch type. (Stephane Eranian)
- Not having the branch type DOES NOT save any space in the
branch record (Stephane Eranian)
- The Arch LBR HW can retrieve the common branch types from the
LBR_INFO. It doesn't require the high overhead SW disassemble.
Fixes: 47125db27e47 ("perf/x86/intel/lbr: Support Architectural LBR")
Reported-by: Stephane Eranian <eranian@xxxxxxxxxx>
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20220816125612.2042397-1-kan.liang@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/events/intel/lbr.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -1114,6 +1114,14 @@ static int intel_pmu_setup_hw_lbr_filter
if (static_cpu_has(X86_FEATURE_ARCH_LBR)) {
reg->config = mask;
+
+ /*
+ * The Arch LBR HW can retrieve the common branch types
+ * from the LBR_INFO. It doesn't require the high overhead
+ * SW disassemble.
+ * Enable the branch type by default for the Arch LBR.
+ */
+ reg->reg |= X86_BR_TYPE_SAVE;
return 0;
}
Patches currently in stable-queue which might be from kan.liang@xxxxxxxxxxxxxxx are
queue-5.10/perf-x86-lbr-enable-the-branch-type-for-the-arch-lbr-by-default.patch
