kvm irqfd: support direct msimessage to irq translation

On PPC64 systems MSI Messages are translated to system IRQ in a PCI
host bridge. This is already supported for emulated MSI/MSIX but
not for irqfd where the current QEMU allocates IRQ numbers from
irqchip and maps MSIMessages to IRQ in the host kernel.

This adds a new direct mapping flag which tells
the kvm_irqchip_add_msi_route() function that a new VIRQ
should not be allocated, instead the value from MSIMessage::data
should be used. It is up to the platform code to make sure that
this contains a valid IRQ number as sPAPR does in spapr_pci.c.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/sysemu/kvm.h

@@ -46,6 +46,7 @@ extern bool kvm_halt_in_kernel_allowed;
 extern bool kvm_irqfds_allowed;
 extern bool kvm_msi_via_irqfd_allowed;
 extern bool kvm_gsi_routing_allowed;
+extern bool kvm_gsi_direct_mapping;
 extern bool kvm_readonly_mem_allowed;
 
 #if defined CONFIG_KVM || !defined NEED_CPU_H
@@ -107,6 +108,13 @@ extern bool kvm_readonly_mem_allowed;
  */
 #define kvm_gsi_routing_enabled() (kvm_gsi_routing_allowed)
 
+/**
+ * kvm_gsi_direct_mapping:
+ *
+ * Returns: true if GSI direct mapping is enabled.
+ */
+#define kvm_gsi_direct_mapping() (kvm_gsi_direct_mapping)
+
 /**
  * kvm_readonly_mem_enabled:
  *
@@ -123,6 +131,7 @@ extern bool kvm_readonly_mem_allowed;
 #define kvm_irqfds_enabled() (false)
 #define kvm_msi_via_irqfd_enabled() (false)
 #define kvm_gsi_routing_allowed() (false)
+#define kvm_gsi_direct_mapping() (false)
 #define kvm_readonly_mem_enabled() (false)
 #endif
 

kvm-all.c

@@ -111,6 +111,7 @@ bool kvm_halt_in_kernel_allowed;
 bool kvm_irqfds_allowed;
 bool kvm_msi_via_irqfd_allowed;
 bool kvm_gsi_routing_allowed;
+bool kvm_gsi_direct_mapping;
 bool kvm_allowed;
 bool kvm_readonly_mem_allowed;
 
@@ -1069,6 +1070,10 @@ void kvm_irqchip_release_virq(KVMState *s, int virq)
     struct kvm_irq_routing_entry *e;
     int i;
 
+    if (kvm_gsi_direct_mapping()) {
+        return;
+    }
+
     for (i = 0; i < s->irq_routes->nr; i++) {
         e = &s->irq_routes->entries[i];
         if (e->gsi == virq) {
@@ -1190,6 +1195,10 @@ int kvm_irqchip_add_msi_route(KVMState *s, MSIMessage msg)
     struct kvm_irq_routing_entry kroute = {};
     int virq;
 
+    if (kvm_gsi_direct_mapping()) {
+        return msg.data & 0xffff;
+    }
+
     if (!kvm_gsi_routing_enabled()) {
         return -ENOSYS;
     }
@@ -1216,6 +1225,10 @@ int kvm_irqchip_update_msi_route(KVMState *s, int virq, MSIMessage msg)
 {
     struct kvm_irq_routing_entry kroute = {};
 
+    if (kvm_gsi_direct_mapping()) {
+        return 0;
+    }
+
     if (!kvm_irqchip_in_kernel()) {
         return -ENOSYS;
     }

kvm-stub.c

@@ -25,6 +25,7 @@ bool kvm_async_interrupts_allowed;
 bool kvm_irqfds_allowed;
 bool kvm_msi_via_irqfd_allowed;
 bool kvm_gsi_routing_allowed;
+bool kvm_gsi_direct_mapping;
 bool kvm_allowed;
 bool kvm_readonly_mem_allowed;