perf/x86/intel: Expose existence of callback support to KVM

Add a "has_callstack" field to the x86_pmu_lbr structure used to pass
information to KVM, and set it accordingly in x86_perf_get_lbr().  KVM
will use has_callstack to avoid trying to create perf LBR events with
PERF_SAMPLE_BRANCH_CALL_STACK on CPUs that don't support callstacks.

Reviewed-by: Mingwei Zhang <mizhang@google.com>
Link: https://lore.kernel.org/r/20240307011344.835640-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/events/intel/lbr.c

@@ -1693,6 +1693,7 @@ void x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
 	lbr->from = x86_pmu.lbr_from;
 	lbr->to = x86_pmu.lbr_to;
 	lbr->info = x86_pmu.lbr_info;
+	lbr->has_callstack = x86_pmu_has_lbr_callstack();
 }
 EXPORT_SYMBOL_GPL(x86_perf_get_lbr);
 

arch/x86/include/asm/perf_event.h

@@ -555,6 +555,7 @@ struct x86_pmu_lbr {
 	unsigned int	from;
 	unsigned int	to;
 	unsigned int	info;
+	bool		has_callstack;
 };
 
 extern void perf_get_x86_pmu_capability(struct x86_pmu_capability *cap);