On systems where PT does not coexist with VMX, users get confused when
PT turns up with no data because they forgot they're running a kvm
session at the same time.
This patch adds a preemptive check for any active VMX operations that
will fail event creation. This does not provide any guarantees or
protection against racing with a kvm starting in parallel, but is
intended to serve as a hint for the user. If VMXON happens after an
event had been created, the event will still produce an empty trace.
Signed-off-by: Alexander Shishkin <alexander.shish...@linux.intel.com>
Reported-by: Andi Kleen <a...@linux.intel.com>
---
arch/x86/events/intel/pt.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index 9372fa4549..b1490a879c 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -1444,6 +1444,20 @@ static void pt_event_destroy(struct perf_event *event)
static int pt_event_init(struct perf_event *event)
{
+ int cpu, vmx_on = 0;
+
+ get_online_cpus();
+ for_each_online_cpu(cpu) {
+ struct pt *pt = per_cpu_ptr(&pt_ctx, cpu);
+
+ if (READ_ONCE(pt->vmx_on))
+ vmx_on++;
+ }
+ put_online_cpus();
+
+ if (vmx_on)
+ return -EBUSY;
+
if (event->attr.type != pt_pmu.pmu.type)
return -ENOENT;
--
2.11.0
