Re: [PATCH 06/15] KVM: x86: Register perf callbacks only when actively handling interrupt
From: Peter Zijlstra <peterz@infradead.org>
Date: 2021-08-27 07:25:34
Also in:
kvm, kvmarm, linux-arm-kernel, linux-riscv, lkml, xen-devel
On Thu, Aug 26, 2021 at 05:57:09PM -0700, Sean Christopherson wrote:
quoted hunk ↗ jump to hunk
diff --git a/kernel/events/core.c b/kernel/events/core.c index 9bc1375d6ed9..2f28d9d8dc94 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c@@ -6485,6 +6485,18 @@ static void perf_pending_event(struct irq_work *entry) #ifdef CONFIG_HAVE_GUEST_PERF_EVENTS DEFINE_PER_CPU(struct perf_guest_info_callbacks *, perf_guest_cbs); +void __perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) +{ + __this_cpu_write(perf_guest_cbs, cbs); +} +EXPORT_SYMBOL_GPL(__perf_register_guest_info_callbacks); + +void __perf_unregister_guest_info_callbacks(void) +{ + __this_cpu_write(perf_guest_cbs, NULL); +} +EXPORT_SYMBOL_GPL(__perf_unregister_guest_info_callbacks);
This is 100% broken, and a prime example of why I hate modules. It provides an interface for all modules, and completely fails to validate even the most basic usage. By using __this_cpu*() it omits the preemption checks, so you can call this with preemption enabled, no problem. By not checking the previous state, multiple modules can call this interleaved without issue. Basically assume any EXPORTed function is hostile, binary modules and out-of-tree modules *are* just that. It's a cesspit out there.