lkml.org 
[lkml]   [2022]   [Feb]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v4 09/17] perf/core: Use static_call to optimize perf_guest_info_callbacks
+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@infradead.org>
> Cc: Like Xu <like.xu.linux@gmail.com>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---

...

> 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$

\
 
 \ /
  Last update: 2022-02-02 19:44    [W:0.160 / U:2.396 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site