Commit 085f6be2 authored by Kim Phillips's avatar Kim Phillips Committed by Greg Kroah-Hartman
Browse files

arch/x86/amd/ibs: Fix re-arming IBS Fetch

commit 221bfce5ebbdf72ff08b3bf2510ae81058ee568b upstream.

Stephane Eranian found a bug in that IBS' current Fetch counter was not
being reset when the driver would write the new value to clear it along
with the enable bit set, and found that adding an MSR write that would
first disable IBS Fetch would make IBS Fetch reset its current count.

Indeed, the PPR for AMD Family 17h Model 31h B0 55803 Rev 0.54 - Sep 12,
2019 states "The periodic fetch counter is set to IbsFetchCnt [...] when
IbsFetchEn is changed from 0 to 1."

Explicitly set IbsFetchEn to 0 and then to 1 when re-enabling IBS Fetch,
so the driver properly resets the internal counter to 0 and IBS
Fetch starts counting again.

A family 15h machine tested does not have this problem, and the extra
wrmsr is also not needed on Family 19h, so only do the extra wrmsr on
families 16h through 18h.
Reported-by: default avatarStephane Eranian <>
Signed-off-by: default avatarKim Phillips <>
[peterz: optimized]
Signed-off-by: default avatarPeter Zijlstra (Intel) <>

Signed-off-by: default avatarGreg Kroah-Hartman <>
parent b4818cfc
......@@ -89,6 +89,7 @@ struct perf_ibs {
u64 max_period;
unsigned long offset_mask[1];
int offset_max;
unsigned int fetch_count_reset_broken : 1;
struct cpu_perf_ibs __percpu *pcpu;
struct attribute **format_attrs;
......@@ -363,7 +364,12 @@ perf_ibs_event_update(struct perf_ibs *perf_ibs, struct perf_event *event,
static inline void perf_ibs_enable_event(struct perf_ibs *perf_ibs,
struct hw_perf_event *hwc, u64 config)
wrmsrl(hwc->config_base, hwc->config | config | perf_ibs->enable_mask);
u64 tmp = hwc->config | config;
if (perf_ibs->fetch_count_reset_broken)
wrmsrl(hwc->config_base, tmp & ~perf_ibs->enable_mask);
wrmsrl(hwc->config_base, tmp | perf_ibs->enable_mask);
......@@ -733,6 +739,13 @@ static __init void perf_event_ibs_init(void)
struct attribute **attr = ibs_op_format_attrs;
* Some chips fail to reset the fetch count when it is written; instead
* they need a 0-1 transition of IbsFetchEn.
if (boot_cpu_data.x86 >= 0x16 && boot_cpu_data.x86 <= 0x18)
perf_ibs_fetch.fetch_count_reset_broken = 1;
perf_ibs_pmu_init(&perf_ibs_fetch, "ibs_fetch");
if (ibs_caps & IBS_CAPS_OPCNT) {
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