+Will and Sami, -most everyone else On Thu, Nov 11, 2021, Sean Christopherson wrote: > Use static_call to optimize perf's guest callbacks on arm64 and x86, > which are now the only architectures that define the callbacks. Use > DEFINE_STATIC_CALL_RET0 as the default/NULL for all guest callbacks, as > the callback semantics are that a return value '0' means "not in guest". > > static_call obviously avoids the overhead of CONFIG_RETPOLINE=y, but is > also advantageous versus other solutions, e.g. per-cpu callbacks, in that > a per-cpu memory load is not needed to detect the !guest case. > > Based on code from Peter and Like. > > Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > Cc: Like Xu <like.xu.linux@xxxxxxxxx> > Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > --- ... > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 1c8d341ecc77..b4fd928e4ff8 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -6524,12 +6524,23 @@ static void perf_pending_event(struct irq_work *entry) > #ifdef CONFIG_GUEST_PERF_EVENTS > struct perf_guest_info_callbacks __rcu *perf_guest_cbs; > > +DEFINE_STATIC_CALL_RET0(__perf_guest_state, *perf_guest_cbs->state); > +DEFINE_STATIC_CALL_RET0(__perf_guest_get_ip, *perf_guest_cbs->get_ip); > +DEFINE_STATIC_CALL_RET0(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr); Using __static_call_return0() makes clang's CFI sad on arm64 due to the resulting function prototype mistmatch, which IIUC, is verified by clang's __cfi_check() for indirect calls, i.e. architectures without CONFIG_HAVE_STATIC_CALL. We could fudge around the issue by using stubs, massaging prototypes, etc..., but that means doing that for every arch-agnostic user of __static_call_return0(). Any clever ideas? Can we do something like generate a unique function for every DEFINE_STATIC_CALL_RET0 for CONFIG_HAVE_STATIC_CALL=n, e.g. using typeof() to get the prototype? Kernel panic - not syncing: CFI failure (target: __static_call_return0+0x0/0x8) CPU: 0 PID: 1625 Comm: batterystats-wo Tainted: G W OE 5.16.0-mainline #1$ Hardware name: Raven EVT 1.1 (DT)$ Call trace:$ dump_backtrace+0xf0/0x130$ show_stack+0x1c/0x2c$ dump_stack_lvl+0x68/0x98$ panic+0x168/0x420$ __cfi_check_fail+0x58/0x5c$ __cfi_slowpath_diag+0x150/0x1a4$ perf_misc_flags+0x74/0xa4$ perf_prepare_sample+0x50/0x44c$ perf_event_output_forward+0x5c/0xcc$ __perf_event_overflow+0xc8/0x188$ perf_swevent_event+0x7c/0x10c$ perf_tp_event+0x168/0x298$ perf_trace_run_bpf_submit+0x8c/0xdc$ perf_trace_sched_switch+0x180/0x1cc$ __schedule+0x850/0x924$ schedule+0x98/0xe0$ binder_wait_for_work+0x158/0x368$ binder_thread_read+0x278/0x243c$ binder_ioctl_write_read+0x120/0x45c$ binder_ioctl+0x1ac/0xc34$ __arm64_sys_ioctl+0xa8/0x118$ invoke_syscall+0x64/0x178$ el0_svc_common+0x8c/0x100$ do_el0_svc+0x28/0xa0$ el0_svc+0x24/0x84$ el0t_64_sync_handler+0x88/0xec$ el0t_64_sync+0x1b4/0x1b8$
