The following commit has been merged into the perf/core branch of tip:

Commit-ID: 221bfce5ebbdf72ff08b3bf2510ae81058ee568b Gitweb: https://git.kernel.org/tip/221bfce5ebbdf72ff08b3bf2510ae81058ee568b Author: Kim Phillips kim.phillips@amd.com AuthorDate: Tue, 08 Sep 2020 16:47:36 -05:00 Committer: Peter Zijlstra peterz@infradead.org CommitterDate: Thu, 10 Sep 2020 11:19:36 +02:00

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

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: Stephane Eranian stephane.eranian@google.com Signed-off-by: Kim Phillips kim.phillips@amd.com [peterz: optimized] Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: stable@vger.kernel.org Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 --- arch/x86/events/amd/ibs.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c index ea323dc..40669ea 100644 --- a/arch/x86/events/amd/ibs.c +++ b/arch/x86/events/amd/ibs.c @@ -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; @@ -370,7 +371,12 @@ 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); }

/* @@ -756,6 +762,13 @@ 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) {