Re: [PATCH RFC 0/2] ignore LBR-related MSRs

[Jiri Olsa]

On Wed, Dec 06, 2017 at 02:43:01PM +0300, Jan Dakinevich wrote:
> w2k16 essentials fails to boot if underlying hypervisor lacks of support for 
> LBR MSRs. To workaround the issue, it suggessted to ignore these MSRs (but not 
> all).
> 
> The information, which MSRs are supported for specific platform is taken from
> perf, it is the subject of the first patch. The second patch adds ignoring for
> these MSRs to pmu_intel code of KVM.
> 
> TODO: use MSR load/store areas to make full support of LBR debug.
> 
> Jan Dakinevich (2):
>   perf/x86/intel: make reusable LBR initialization code
>   KVM: x86/vPMU: ignore access to LBR-related MSRs
> 
>  arch/x86/events/core.c            |   8 +-
>  arch/x86/events/intel/core.c      |  59 +++------
>  arch/x86/events/intel/lbr.c       | 272 +++++++++++++++++++++++++-------------
>  arch/x86/events/perf_event.h      |  27 +---
>  arch/x86/include/asm/kvm_host.h   |   2 +
>  arch/x86/include/asm/perf_event.h |  11 ++
>  arch/x86/kvm/pmu_intel.c          |  33 +++++
>  7 files changed, 250 insertions(+), 162 deletions(-)

unrelated, but while looking on this, dont we miss task_ctx_data
allocation for child context? like in attached change

jirka


---
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 494eca1bc760..7c5de1160545 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10699,6 +10699,7 @@ const struct perf_event_attr *perf_event_attrs(struct perf_event *event)
 	      struct perf_event_context *child_ctx)
 {
 	enum perf_event_state parent_state = parent_event->state;
+	void *task_ctx_data = NULL;
 	struct perf_event *child_event;
 	unsigned long flags;
 
@@ -10719,6 +10720,19 @@ const struct perf_event_attr *perf_event_attrs(struct perf_event *event)
 	if (IS_ERR(child_event))
 		return child_event;
 
+
+	if ((child_event->attach_state & PERF_ATTACH_TASK_DATA) &&
+	    !child_ctx->task_ctx_data) {
+		struct pmu *pmu = child_event->pmu;
+
+		task_ctx_data = kzalloc(pmu->task_ctx_size, GFP_KERNEL);
+		if (!task_ctx_data) {
+			free_event(child_event);
+			return NULL;
+		}
+		child_ctx->task_ctx_data = task_ctx_data;
+	}
+
 	/*
 	 * is_orphaned_event() and list_add_tail(&parent_event->child_list)
 	 * must be under the same lock in order to serialize against
@@ -10729,6 +10743,7 @@ const struct perf_event_attr *perf_event_attrs(struct perf_event *event)
 	if (is_orphaned_event(parent_event) ||
 	    !atomic_long_inc_not_zero(&parent_event->refcount)) {
 		mutex_unlock(&parent_event->child_mutex);
+		/* task_ctx_data is freed with child_ctx */
 		free_event(child_event);
 		return NULL;
 	}