[PATCH] x86: kvm: Initialize static calls before SMP boot

[David Sauerwein]

Updating static calls is expensive on wide SMP systems because all
online CPUs need to act in a coordinated manner for code patching to
work as expected.

Static are initialized only after SMP boot, where the code patching
overhead is noticeable. Pre-initialize the majority of these static
calls before SMP boot to get rid of that overhead.

The pre-initialization most likely already sets the correct value. To
still handle any potential differences, make the static call
initialization re-entrant so that the differences are corrected during
post-SMP-boot initialization. Values that are already set correctly are
skipped.

This patch was tested on a 6th Gen Intel Xeon Platinum 8375C CPU with
128 SMT cores. When comparing before and after we see that 85% less time
is spent in kvm_ops_update (29.5ms -> 4.2ms).

Co-developed-by: Jan H. Schönherr <jschoenh@xxxxxxxxx>
Signed-off-by: Jan H. Schönherr <jschoenh@xxxxxxxxx>
Signed-off-by: David Sauerwein <dssauerw@xxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/svm/svm.c          | 11 +++++++++++
 arch/x86/kvm/vmx/vmx.c          | 18 ++++++++++++++++++
 arch/x86/kvm/x86.c              | 19 ++++++++++++++++++-
 kernel/events/core.c            |  6 +++++-
 5 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 48598d017d6f..18072d7bed36 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2000,6 +2000,7 @@ extern struct kvm_x86_ops kvm_x86_ops;
 #define KVM_X86_OP_OPTIONAL_RET0 KVM_X86_OP
 #include <asm/kvm-x86-ops.h>
 
+int kvm_x86_vendor_init_early(struct kvm_x86_init_ops *ops);
 int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops);
 void kvm_x86_vendor_exit(void);
 
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 9d29b2e7e855..de7aa4d1f0e6 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5452,6 +5452,17 @@ static void __svm_exit(void)
 	kvm_x86_vendor_exit();
 }
 
+#ifndef MODULE
+static int __init svm_ops_early_init(void)
+{
+	if (!kvm_is_svm_supported())
+		return -EOPNOTSUPP;
+
+	return kvm_x86_vendor_init_early(&svm_init_ops);
+}
+early_initcall(svm_ops_early_init);
+#endif
+
 static int __init svm_init(void)
 {
 	int r;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 91b6f2f3edc2..569545854e16 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -8617,6 +8617,8 @@ __init int vmx_hardware_setup(void)
 		vt_x86_ops.set_hv_timer = NULL;
 		vt_x86_ops.cancel_hv_timer = NULL;
 	}
+	WARN_ON(enable_preemption_timer && vt_x86_ops.set_hv_timer == NULL);
+	WARN_ON(enable_preemption_timer && vt_x86_ops.cancel_hv_timer == NULL);
 
 	kvm_caps.supported_mce_cap |= MCG_LMCE_P;
 	kvm_caps.supported_mce_cap |= MCG_CMCI_P;
@@ -8698,6 +8700,22 @@ void vmx_exit(void)
 	kvm_x86_vendor_exit();
 }
 
+#ifndef MODULE
+static int __init vmx_ops_early_init(void)
+{
+	if (!kvm_is_vmx_supported())
+		return -EOPNOTSUPP;
+
+	if (!enable_preemption_timer) {
+		vt_x86_ops.set_hv_timer = NULL;
+		vt_x86_ops.cancel_hv_timer = NULL;
+	}
+
+	return kvm_x86_vendor_init_early(&vt_init_ops);
+}
+early_initcall(vmx_ops_early_init);
+#endif
+
 int __init vmx_init(void)
 {
 	int r, cpu;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c9c2aa6f4705..dbd00a26538f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9971,6 +9971,22 @@ static void kvm_x86_check_cpu_compat(void *ret)
 	*(int *)ret = kvm_x86_check_processor_compatibility();
 }
 
+int kvm_x86_vendor_init_early(struct kvm_x86_init_ops *ops)
+{
+	guard(mutex)(&vendor_module_lock);
+
+	if (kvm_x86_ops.enable_virtualization_cpu) {
+		pr_err("already loaded vendor module '%s'\n", kvm_x86_ops.name);
+		return -EEXIST;
+	}
+
+	kvm_ops_update(ops);
+	kvm_register_perf_callbacks(ops->handle_intel_pt_intr);
+
+	return 0;
+}
+EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_x86_vendor_init_early);
+
 int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 {
 	u64 host_pat;
@@ -9978,7 +9994,8 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 
 	guard(mutex)(&vendor_module_lock);
 
-	if (kvm_x86_ops.enable_virtualization_cpu) {
+	if (kvm_x86_ops.enable_virtualization_cpu &&
+	    kvm_x86_ops.enable_virtualization_cpu != ops->runtime_ops->enable_virtualization_cpu) {
 		pr_err("already loaded vendor module '%s'\n", kvm_x86_ops.name);
 		return -EEXIST;
 	}
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2c35acc2722b..731975791895 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7378,7 +7378,8 @@ DEFINE_STATIC_CALL_RET0(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->hand
 
 void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
 {
-	if (WARN_ON_ONCE(rcu_access_pointer(perf_guest_cbs)))
+	if (WARN_ON_ONCE(rcu_access_pointer(perf_guest_cbs) &&
+		rcu_access_pointer(perf_guest_cbs) != cbs))
 		return;
 
 	rcu_assign_pointer(perf_guest_cbs, cbs);
@@ -7389,6 +7390,9 @@ void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
 	if (cbs->handle_intel_pt_intr)
 		static_call_update(__perf_guest_handle_intel_pt_intr,
 				   cbs->handle_intel_pt_intr);
+	else
+		static_call_update(__perf_guest_handle_intel_pt_intr,
+				   (void *)__static_call_return0);
 }
 EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
 
-- 
2.47.3




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