On Fri, Aug 27, 2021 at 02:52:25PM +0800, Like Xu wrote:

+ STATIC BRANCH/CALL friends.

On 27/8/2021 8:57 am, Sean Christopherson wrote:

quoted

This started out as a small series[1] to fix a KVM bug related to Intel PT
interrupt handling and snowballed horribly.

The main problem being addressed is that the perf_guest_cbs are shared by
all CPUs, can be nullified by KVM during module unload, and are not
protected against concurrent access from NMI context.

Shouldn't this be a generic issue of the static_call() usage ?

At the beginning, we set up the static entry assuming perf_guest_cbs != NULL:

	if (perf_guest_cbs && perf_guest_cbs->handle_intel_pt_intr) {
		static_call_update(x86_guest_handle_intel_pt_intr,
				   perf_guest_cbs->handle_intel_pt_intr);
	}

and then we unset the perf_guest_cbs and do the static function call like this:

DECLARE_STATIC_CALL(x86_guest_handle_intel_pt_intr,
*(perf_guest_cbs->handle_intel_pt_intr));
static int handle_pmi_common(struct pt_regs *regs, u64 status)
{
		...
		if (!static_call(x86_guest_handle_intel_pt_intr)())
			intel_pt_interrupt();
		...
}

You just have to make sure all static_call() invocations that started
before unreg are finished before continuing with the unload.
synchronize_rcu() can help with that.

This is module unload 101. Nothing specific to static_call().