KVM: Use the scheduler preemption notifiers to make kvm preemptible

Current kvm disables preemption while the new virtualization registers are
in use.  This of course is not very good for latency sensitive workloads (one
use of virtualization is to offload user interface and other latency
insensitive stuff to a container, so that it is easier to analyze the
remaining workload).  This patch re-enables preemption for kvm; preemption
is now only disabled when switching the registers in and out, and during
the switch to guest mode and back.

Contains fixes from Shaohua Li <shaohua.li@intel.com>.

Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 37 insertions, 6 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 20947462f401..6035e6d35417 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -54,6 +54,8 @@ static cpumask_t cpus_hardware_enabled;
 
 struct kvm_arch_ops *kvm_arch_ops;
 
+static __read_mostly struct preempt_ops kvm_preempt_ops;
+
 #define STAT_OFFSET(x) offsetof(struct kvm_vcpu, stat.x)
 
 static struct kvm_stats_debugfs_item {
@@ -239,13 +241,21 @@ EXPORT_SYMBOL_GPL(kvm_put_guest_fpu);
  */
 static void vcpu_load(struct kvm_vcpu *vcpu)
 {
+        int cpu;
+
         mutex_lock(&vcpu->mutex);
-        kvm_arch_ops->vcpu_load(vcpu);
+        cpu = get_cpu();
+        preempt_notifier_register(&vcpu->preempt_notifier);
+        kvm_arch_ops->vcpu_load(vcpu, cpu);
+        put_cpu();
 }
 
 static void vcpu_put(struct kvm_vcpu *vcpu)
 {
+        preempt_disable();
         kvm_arch_ops->vcpu_put(vcpu);
+        preempt_notifier_unregister(&vcpu->preempt_notifier);
+        preempt_enable();
         mutex_unlock(&vcpu->mutex);
 }
 
@@ -1672,9 +1682,7 @@ void kvm_resched(struct kvm_vcpu *vcpu)
 {
         if (!need_resched())
                 return;
-        vcpu_put(vcpu);
         cond_resched();
-        vcpu_load(vcpu);
 }
 EXPORT_SYMBOL_GPL(kvm_resched);
 
@@ -1722,11 +1730,9 @@ static int pio_copy_data(struct kvm_vcpu *vcpu)
         unsigned bytes;
         int nr_pages = vcpu->pio.guest_pages[1] ? 2 : 1;
 
-        kvm_arch_ops->vcpu_put(vcpu);
         q = vmap(vcpu->pio.guest_pages, nr_pages, VM_READ|VM_WRITE,
                  PAGE_KERNEL);
         if (!q) {
-                kvm_arch_ops->vcpu_load(vcpu);
                 free_pio_guest_pages(vcpu);
                 return -ENOMEM;
         }
@@ -1738,7 +1744,6 @@ static int pio_copy_data(struct kvm_vcpu *vcpu)
                 memcpy(p, q, bytes);
         q -= vcpu->pio.guest_page_offset;
         vunmap(q);
-        kvm_arch_ops->vcpu_load(vcpu);
         free_pio_guest_pages(vcpu);
         return 0;
 }
@@ -2413,6 +2418,8 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)
         if (IS_ERR(vcpu))
                 return PTR_ERR(vcpu);
 
+        preempt_notifier_init(&vcpu->preempt_notifier, &kvm_preempt_ops);
+
         vcpu_load(vcpu);
         r = kvm_mmu_setup(vcpu);
         vcpu_put(vcpu);
@@ -3145,6 +3152,27 @@ static struct sys_device kvm_sysdev = {
 
 hpa_t bad_page_address;
 
+static inline
+struct kvm_vcpu *preempt_notifier_to_vcpu(struct preempt_notifier *pn)
+{
+        return container_of(pn, struct kvm_vcpu, preempt_notifier);
+}
+
+static void kvm_sched_in(struct preempt_notifier *pn, int cpu)
+{
+        struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
+
+        kvm_arch_ops->vcpu_load(vcpu, cpu);
+}
+
+static void kvm_sched_out(struct preempt_notifier *pn,
+                          struct task_struct *next)
+{
+        struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
+
+        kvm_arch_ops->vcpu_put(vcpu);
+}
+
 int kvm_init_arch(struct kvm_arch_ops *ops, struct module *module)
 {
         int r;
@@ -3191,6 +3219,9 @@ int kvm_init_arch(struct kvm_arch_ops *ops, struct module *module)
                 goto out_free;
         }
 
+        kvm_preempt_ops.sched_in = kvm_sched_in;
+        kvm_preempt_ops.sched_out = kvm_sched_out;
+
         return r;
 
 out_free: