[patch 3/3] x86: kvm guest side support for KVM_HC_RT_PRIO hypercall

[Marcelo Tosatti]

Add hypercalls to spinlock/unlock to set/unset FIFO priority
for the vcpu, protected by a static branch to avoid performance
increase in the normal kernels.

Enable option by "kvmfifohc" kernel command line parameter (disabled
by default).

Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>

---
 arch/x86/kernel/kvm.c            |   31 +++++++++++++++++++++++++++++++
 include/linux/spinlock.h         |    2 +-
 include/linux/spinlock_api_smp.h |   17 +++++++++++++++++
 3 files changed, 49 insertions(+), 1 deletion(-)

Index: kvm.fifopriohc-submit/arch/x86/kernel/kvm.c
===================================================================
--- kvm.fifopriohc-submit.orig/arch/x86/kernel/kvm.c
+++ kvm.fifopriohc-submit/arch/x86/kernel/kvm.c
@@ -37,6 +37,7 @@
 #include <linux/debugfs.h>
 #include <linux/nmi.h>
 #include <linux/swait.h>
+#include <linux/static_key.h>
 #include <asm/timer.h>
 #include <asm/cpu.h>
 #include <asm/traps.h>
@@ -321,6 +322,36 @@ static notrace void kvm_guest_apic_eoi_w
 	apic->native_eoi_write(APIC_EOI, APIC_EOI_ACK);
 }
 
+static int kvmfifohc;
+
+static int parse_kvmfifohc(char *arg)
+{
+	kvmfifohc = 1;
+	return 0;
+}
+
+early_param("kvmfifohc", parse_kvmfifohc);
+
+DEFINE_STATIC_KEY_FALSE(kvm_fifo_hc_key);
+
+static void kvm_init_fifo_hc(void)
+{
+	long ret;
+
+	ret = kvm_hypercall1(KVM_HC_RT_PRIO, 0);
+
+	if (ret == 0 && kvmfifohc == 1)
+		static_branch_enable(&kvm_fifo_hc_key);
+}
+
+static __init int kvmguest_late_init(void)
+{
+	kvm_init_fifo_hc();
+	return 0;
+}
+
+late_initcall(kvmguest_late_init);
+
 static void kvm_guest_cpu_init(void)
 {
 	if (!kvm_para_available())
Index: kvm.fifopriohc-submit/include/linux/spinlock_api_smp.h
===================================================================
--- kvm.fifopriohc-submit.orig/include/linux/spinlock_api_smp.h
+++ kvm.fifopriohc-submit/include/linux/spinlock_api_smp.h
@@ -136,11 +136,28 @@ static inline void __raw_spin_lock_bh(ra
 	LOCK_CONTENDED(lock, do_raw_spin_trylock, do_raw_spin_lock);
 }
 
+#ifdef CONFIG_KVM_GUEST
+DECLARE_STATIC_KEY_FALSE(kvm_fifo_hc_key);
+#endif
+
 static inline void __raw_spin_lock(raw_spinlock_t *lock)
 {
 	preempt_disable();
+
+#if defined(CONFIG_KVM_GUEST) && defined(CONFIG_SMP)
+	/* enable FIFO priority */
+	if (static_branch_unlikely(&kvm_fifo_hc_key))
+		kvm_hypercall1(KVM_HC_RT_PRIO, 0x1);
+#endif
+
 	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
 	LOCK_CONTENDED(lock, do_raw_spin_trylock, do_raw_spin_lock);
+
+#if defined(CONFIG_KVM_GUEST) && defined(CONFIG_SMP)
+	/* disable FIFO priority */
+	if (static_branch_unlikely(&kvm_fifo_hc_key))
+		kvm_hypercall1(KVM_HC_RT_PRIO, 0);
+#endif
 }
 
 #endif /* !CONFIG_GENERIC_LOCKBREAK || CONFIG_DEBUG_LOCK_ALLOC */
Index: kvm.fifopriohc-submit/include/linux/spinlock.h
===================================================================
--- kvm.fifopriohc-submit.orig/include/linux/spinlock.h
+++ kvm.fifopriohc-submit/include/linux/spinlock.h
@@ -56,7 +56,7 @@
 #include <linux/stringify.h>
 #include <linux/bottom_half.h>
 #include <asm/barrier.h>
-
+#include <uapi/linux/kvm_para.h>
 
 /*
  * Must define these before including other files, inline functions need them