[Qemu-devel] [PATCH v2 1/7] kvm: Decouple 'async interrupt delivery' from 'kernel irqchip'

[Peter Maydell <peter.maydell@linaro.org>]

On x86 userspace delivers interrupts to the kernel asynchronously
(and therefore VCPU idle management is done in the kernel) if and
only if there is an in-kernel irqchip. On other architectures this
isn't necessarily true (they may always send interrupts
asynchronously), so define a new kvm_async_interrupts_enabled()
function instead of misusing kvm_irqchip_in_kernel().

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 cpus.c     |    3 ++-
 kvm-all.c  |    7 ++++++-
 kvm-stub.c |    1 +
 kvm.h      |   13 +++++++++++++
 4 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/cpus.c b/cpus.c
index 756e624..8c54dd0 100644
--- a/cpus.c
+++ b/cpus.c
@@ -69,7 +69,8 @@ static bool cpu_thread_is_idle(CPUArchState *env)
     if (env->stopped || !runstate_is_running()) {
         return true;
     }
-    if (!env->halted || qemu_cpu_has_work(env) || kvm_irqchip_in_kernel()) {
+    if (!env->halted || qemu_cpu_has_work(env) ||
+        kvm_async_interrupts_enabled()) {
         return false;
     }
     return true;
diff --git a/kvm-all.c b/kvm-all.c
index 2148b20..0a38ba1 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -100,6 +100,7 @@ struct KVMState
 
 KVMState *kvm_state;
 bool kvm_kernel_irqchip;
+bool kvm_async_interrupts_allowed;
 
 static const KVMCapabilityInfo kvm_required_capabilites[] = {
     KVM_CAP_INFO(USER_MEMORY),
@@ -857,7 +858,7 @@ int kvm_irqchip_set_irq(KVMState *s, int irq, int level)
     struct kvm_irq_level event;
     int ret;
 
-    assert(kvm_irqchip_in_kernel());
+    assert(kvm_async_interrupts_enabled());
 
     event.level = level;
     event.irq = irq;
@@ -1201,6 +1202,10 @@ static int kvm_irqchip_create(KVMState *s)
         s->irqchip_inject_ioctl = KVM_IRQ_LINE_STATUS;
     }
     kvm_kernel_irqchip = true;
+    /* If we have an in-kernel IRQ chip then we must have asynchronous
+     * interrupt delivery (though the reverse is not necessarily true)
+     */
+    kvm_async_interrupts_allowed = true;
 
     kvm_init_irq_routing(s);
 
diff --git a/kvm-stub.c b/kvm-stub.c
index d23b11c..a7a03e1 100644
--- a/kvm-stub.c
+++ b/kvm-stub.c
@@ -19,6 +19,7 @@
 
 KVMState *kvm_state;
 bool kvm_kernel_irqchip;
+bool kvm_async_interrupts_allowed;
 
 int kvm_init_vcpu(CPUArchState *env)
 {
diff --git a/kvm.h b/kvm.h
index 2617dd5..09818f3 100644
--- a/kvm.h
+++ b/kvm.h
@@ -24,13 +24,26 @@
 
 extern int kvm_allowed;
 extern bool kvm_kernel_irqchip;
+extern bool kvm_async_interrupts_allowed;
 
 #if defined CONFIG_KVM || !defined NEED_CPU_H
 #define kvm_enabled()           (kvm_allowed)
 #define kvm_irqchip_in_kernel() (kvm_kernel_irqchip)
+
+/**
+ * kvm_async_interrupts_enabled:
+ *
+ * Returns: true if we can deliver interrupts to KVM
+ * asynchronously (ie by ioctl from any thread at any time)
+ * rather than having to do interrupt delivery synchronously
+ * (where the vcpu must be stopped at a suitable point first).
+ */
+#define kvm_async_interrupts_enabled() (kvm_async_interrupts_allowed)
+
 #else
 #define kvm_enabled()           (0)
 #define kvm_irqchip_in_kernel() (false)
+#define kvm_async_interrupts_enabled() (false)
 #endif
 
 struct kvm_run;
-- 
1.7.5.4