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, 13 insertions, 9 deletions

diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index 18f9b0b3fb1f..8c87d20f8e39 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -396,6 +396,7 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu)
 static void vmx_load_host_state(struct kvm_vcpu *vcpu)
 {
         struct vcpu_vmx *vmx = to_vmx(vcpu);
+        unsigned long flags;
 
         if (!vmx->host_state.loaded)
                 return;
@@ -408,12 +409,12 @@ static void vmx_load_host_state(struct kvm_vcpu *vcpu)
                  * If we have to reload gs, we must take care to
                  * preserve our gs base.
                  */
-                local_irq_disable();
+                local_irq_save(flags);
                 load_gs(vmx->host_state.gs_sel);
 #ifdef CONFIG_X86_64
                 wrmsrl(MSR_GS_BASE, vmcs_readl(HOST_GS_BASE));
 #endif
-                local_irq_enable();
+                local_irq_restore(flags);
 
                 reload_tss();
         }
@@ -427,15 +428,12 @@ static void vmx_load_host_state(struct kvm_vcpu *vcpu)
  * Switches to specified vcpu, until a matching vcpu_put(), but assumes
  * vcpu mutex is already taken.
  */
-static void vmx_vcpu_load(struct kvm_vcpu *vcpu)
+static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
         struct vcpu_vmx *vmx = to_vmx(vcpu);
         u64 phys_addr = __pa(vmx->vmcs);
-        int cpu;
         u64 tsc_this, delta;
 
-        cpu = get_cpu();
-
         if (vcpu->cpu != cpu)
                 vcpu_clear(vcpu);
 
@@ -480,7 +478,6 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
 {
         vmx_load_host_state(vcpu);
         kvm_put_guest_fpu(vcpu);
-        put_cpu();
 }
 
 static void vmx_fpu_activate(struct kvm_vcpu *vcpu)
@@ -2127,6 +2124,8 @@ again:
         if (unlikely(r))
                 goto out;
 
+        preempt_disable();
+
         if (!vcpu->mmio_read_completed)
                 do_interrupt_requests(vcpu, kvm_run);
 
@@ -2269,6 +2268,9 @@ again:
         vcpu->interrupt_window_open = (vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) & 3) == 0;
 
         asm ("mov %0, %%ds; mov %0, %%es" : : "r"(__USER_DS));
+        vmx->launched = 1;
+
+        preempt_enable();
 
         if (unlikely(fail)) {
                 kvm_run->exit_reason = KVM_EXIT_FAIL_ENTRY;
@@ -2283,7 +2285,6 @@ again:
         if (unlikely(prof_on == KVM_PROFILING))
                 profile_hit(KVM_PROFILING, (void *)vmcs_readl(GUEST_RIP));
 
-        vmx->launched = 1;
         r = kvm_handle_exit(kvm_run, vcpu);
         if (r > 0) {
                 /* Give scheduler a change to reschedule. */
@@ -2372,6 +2373,7 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 {
         int err;
         struct vcpu_vmx *vmx = kzalloc(sizeof(*vmx), GFP_KERNEL);
+        int cpu;
 
         if (!vmx)
                 return ERR_PTR(-ENOMEM);
@@ -2396,9 +2398,11 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 
         vmcs_clear(vmx->vmcs);
 
-        vmx_vcpu_load(&vmx->vcpu);
+        cpu = get_cpu();
+        vmx_vcpu_load(&vmx->vcpu, cpu);
         err = vmx_vcpu_setup(&vmx->vcpu);
         vmx_vcpu_put(&vmx->vcpu);
+        put_cpu();
         if (err)
                 goto free_vmcs;