Re: [PATCH v2 00/13] perf: KVM: Fix, optimize, and clean up callbacks

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Aug 27, 2021 at 05:35:45PM -0700, Sean Christopherson wrote:
> Like Xu (2):
>   perf/core: Rework guest callbacks to prepare for static_call support
>   perf/core: Use static_call to optimize perf_guest_info_callbacks
> 
> Sean Christopherson (11):
>   perf: Ensure perf_guest_cbs aren't reloaded between !NULL check and
>     deref
>   KVM: x86: Register perf callbacks after calling vendor's
>     hardware_setup()
>   KVM: x86: Register Processor Trace interrupt hook iff PT enabled in
>     guest
>   perf: Stop pretending that perf can handle multiple guest callbacks
>   perf: Force architectures to opt-in to guest callbacks
>   KVM: x86: Drop current_vcpu for kvm_running_vcpu + kvm_arch_vcpu
>     variable
>   KVM: x86: More precisely identify NMI from guest when handling PMI
>   KVM: Move x86's perf guest info callbacks to generic KVM
>   KVM: x86: Move Intel Processor Trace interrupt handler to vmx.c
>   KVM: arm64: Convert to the generic perf callbacks
>   KVM: arm64: Drop perf.c and fold its tiny bits of code into arm.c /
>     pmu.c

Lets keep the whole intel_pt crud inside x86...

---
Index: linux-2.6/arch/x86/events/core.c
===================================================================
--- linux-2.6.orig/arch/x86/events/core.c
+++ linux-2.6/arch/x86/events/core.c
@@ -92,7 +92,7 @@ DEFINE_STATIC_CALL_RET0(x86_pmu_guest_ge
 
 DEFINE_STATIC_CALL_RET0(x86_guest_state, *(perf_guest_cbs->state));
 DEFINE_STATIC_CALL_RET0(x86_guest_get_ip, *(perf_guest_cbs->get_ip));
-DEFINE_STATIC_CALL_RET0(x86_guest_handle_intel_pt_intr, *(perf_guest_cbs->handle_intel_pt_intr));
+DEFINE_STATIC_CALL_RET0(x86_guest_handle_intel_pt_intr, unsigned int (*)(void));
 
 void arch_perf_update_guest_cbs(struct perf_guest_info_callbacks *guest_cbs)
 {
@@ -103,14 +103,6 @@ void arch_perf_update_guest_cbs(struct p
 		static_call_update(x86_guest_state, (void *)&__static_call_return0);
 		static_call_update(x86_guest_get_ip, (void *)&__static_call_return0);
 	}
-
-	/* Implementing ->handle_intel_pt_intr is optional. */
-	if (guest_cbs && guest_cbs->handle_intel_pt_intr)
-		static_call_update(x86_guest_handle_intel_pt_intr,
-				   guest_cbs->handle_intel_pt_intr);
-	else
-		static_call_update(x86_guest_handle_intel_pt_intr,
-				   (void *)&__static_call_return0);
 }
 
 u64 __read_mostly hw_cache_event_ids
Index: linux-2.6/arch/x86/events/intel/core.c
===================================================================
--- linux-2.6.orig/arch/x86/events/intel/core.c
+++ linux-2.6/arch/x86/events/intel/core.c
@@ -2782,7 +2782,7 @@ static void intel_pmu_reset(void)
 	local_irq_restore(flags);
 }
 
-DECLARE_STATIC_CALL(x86_guest_handle_intel_pt_intr, *(perf_guest_cbs->handle_intel_pt_intr));
+DECLARE_STATIC_CALL(x86_guest_handle_intel_pt_intr, unsigned int (*)(void));
 
 static int handle_pmi_common(struct pt_regs *regs, u64 status)
 {
Index: linux-2.6/arch/x86/kvm/x86.c
===================================================================
--- linux-2.6.orig/arch/x86/kvm/x86.c
+++ linux-2.6/arch/x86/kvm/x86.c
@@ -10960,7 +10960,14 @@ int kvm_arch_hardware_setup(void *opaque
 	memcpy(&kvm_x86_ops, ops->runtime_ops, sizeof(kvm_x86_ops));
 	kvm_ops_static_call_update();
 
-	kvm_register_perf_callbacks(ops->handle_intel_pt_intr);
+	kvm_register_perf_callbacks();
+	if (ops->handle_intel_pt_intr) {
+		static_call_update(x86_guest_handle_intel_pt_intr,
+				   ops->handle_intel_pt_intr);
+	} else {
+		static_call_update(x86_guest_handle_intel_pt_intr,
+				   (void *)&__static_call_return0);
+	}
 
 	if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
 		supported_xss = 0;
Index: linux-2.6/include/linux/perf_event.h
===================================================================
--- linux-2.6.orig/include/linux/perf_event.h
+++ linux-2.6/include/linux/perf_event.h
@@ -32,7 +32,6 @@
 struct perf_guest_info_callbacks {
 	unsigned int			(*state)(void);
 	unsigned long			(*get_ip)(void);
-	unsigned int			(*handle_intel_pt_intr)(void);
 };
 
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
Index: linux-2.6/virt/kvm/kvm_main.c
===================================================================
--- linux-2.6.orig/virt/kvm/kvm_main.c
+++ linux-2.6/virt/kvm/kvm_main.c
@@ -5374,12 +5374,10 @@ static unsigned long kvm_guest_get_ip(vo
 static struct perf_guest_info_callbacks kvm_guest_cbs = {
 	.state			= kvm_guest_state,
 	.get_ip			= kvm_guest_get_ip,
-	.handle_intel_pt_intr	= NULL,
 };
 
-void kvm_register_perf_callbacks(unsigned int (*pt_intr_handler)(void))
+void kvm_register_perf_callbacks(void)
 {
-	kvm_guest_cbs.handle_intel_pt_intr = pt_intr_handler;
 	perf_register_guest_info_callbacks(&kvm_guest_cbs);
 }
 #endif
Index: linux-2.6/arch/arm64/kvm/arm.c
===================================================================
--- linux-2.6.orig/arch/arm64/kvm/arm.c
+++ linux-2.6/arch/arm64/kvm/arm.c
@@ -1749,7 +1749,7 @@ static int init_subsystems(void)
 		goto out;
 
 	kvm_pmu_init();
-	kvm_register_perf_callbacks(NULL);
+	kvm_register_perf_callbacks();
 
 	kvm_sys_reg_table_init();
 
Index: linux-2.6/include/linux/kvm_host.h
===================================================================
--- linux-2.6.orig/include/linux/kvm_host.h
+++ linux-2.6/include/linux/kvm_host.h
@@ -1121,7 +1121,7 @@ static inline bool kvm_arch_intc_initial
 #ifdef __KVM_WANT_PERF_CALLBACKS
 unsigned long kvm_arch_vcpu_get_ip(struct kvm_vcpu *vcpu);
 
-void kvm_register_perf_callbacks(unsigned int (*pt_intr_handler)(void));
+void kvm_register_perf_callbacks(void);
 static inline void kvm_unregister_perf_callbacks(void)
 {
 	perf_unregister_guest_info_callbacks();