On Thu, Dec 08, 2016 at 04:14:17PM -0800, Andi Kleen wrote:
> From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
>
> An earlier patch allowed enabling PT and LBR at the same
> time on Goldmont. However it also allowed enabling BTS and LBR
> at the same time, which is still not supported. Fix this by
> bypassing the check only for PT.
>
> Marking for stable because this allows crashing kernels. Also
> should be merged for 4.9.
>
> Fixes: ccbebba4c6bf ("erf/x86/intel/pt: Bypass PT vs. LBR exclusivity if the core supports it")
> Cc: alexander.shishkin@xxxxxxxxx
> Cc: kan.liang@xxxxxxxxx
> Cc: <stable@xxxxxxxxxxxxxxx>
> v2: Paint bike shed differently.
Now, if only you'd also clarified the point I asked about. By
documenting these cases we not only get easier to read code, but can
also verify if the code does what is intended.
> Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> ---
Changed that to the below, which is more explicit on the what is and is
not allowed. And fixed the definition of lbr_pt_coexist.
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -365,7 +365,11 @@ int x86_add_exclusive(unsigned int what)
{
int i;
- if (x86_pmu.lbr_pt_coexist)
+ /*
+ * When lbr_pt_coexist we allow PT to coexist with either LBR or BTS.
+ * LBR and BTS are still mutually exclusive.
+ */
+ if (x86_pmu.lbr_pt_coexist && what == x86_lbr_exclusive_pt)
return 0;
if (!atomic_inc_not_zero(&x86_pmu.lbr_exclusive[what])) {
@@ -388,7 +392,7 @@ int x86_add_exclusive(unsigned int what)
void x86_del_exclusive(unsigned int what)
{
- if (x86_pmu.lbr_pt_coexist)
+ if (x86_pmu.lbr_pt_coexist && what == x86_lbr_exclusive_pt)
return;
atomic_dec(&x86_pmu.lbr_exclusive[what]);
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -604,7 +604,7 @@ struct x86_pmu {
u64 lbr_sel_mask; /* LBR_SELECT valid bits */
const int *lbr_sel_map; /* lbr_select mappings */
bool lbr_double_abort; /* duplicated lbr aborts */
- bool lbr_pt_coexist; /* LBR may coexist with PT */
+ bool lbr_pt_coexist; /* (LBR|BTS) may coexist with PT */
/*
* Intel PT/LBR/BTS are exclusive
--
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