[Qemu-devel] [PATCH v8 19/19] hw/vfio/platform: add forwarded irq support

[Eric Auger <eric.auger@linaro.org>]

Tests whether the forwarded IRQ modality is available.
In the positive device IRQs are forwarded. This control is
achieved with KVM-VFIO device. with such a modality injection
still is handled through irqfds. However end of interrupt is
not trapped anymore. As soon as the guest completes its virtual
IRQ, the corresponding physical IRQ is completed and the same
physical IRQ can hit again.

A new x-forward property enables to force forwarding off although
enabled by the kernel.

Signed-off-by: Eric Auger <eric.auger@linaro.org>
---
 hw/vfio/platform.c              | 52 +++++++++++++++++++++++++++++++++++++++++
 include/hw/vfio/vfio-platform.h |  2 ++
 trace-events                    |  1 +
 3 files changed, 55 insertions(+)

diff --git a/hw/vfio/platform.c b/hw/vfio/platform.c
index 97d98bf..7881b9b 100644
--- a/hw/vfio/platform.c
+++ b/hw/vfio/platform.c
@@ -237,6 +237,52 @@ static int vfio_start_eventfd_injection(VFIOINTp *intp)
 }
 
 /*
+ * Functions used with forwarding capability
+ */
+
+#ifdef CONFIG_KVM
+
+static bool has_kvm_vfio_forward_capability(void)
+{
+    struct kvm_device_attr attr = {
+         .group = KVM_DEV_VFIO_DEVICE,
+         .attr = KVM_DEV_VFIO_DEVICE_FORWARD_IRQ};
+
+    if (ioctl(vfio_kvm_device_fd, KVM_HAS_DEVICE_ATTR, &attr) == 0) {
+        return true;
+    } else {
+        return false;
+    }
+}
+
+static int vfio_set_forwarding(VFIOINTp *intp)
+{
+    int ret;
+    struct kvm_device_attr attr = {
+         .group = KVM_DEV_VFIO_DEVICE,
+         .attr = KVM_DEV_VFIO_DEVICE_FORWARD_IRQ};
+
+    intp->fwd_irq = g_malloc0(sizeof(*intp->fwd_irq));
+    intp->fwd_irq->fd = intp->vdev->vbasedev.fd;
+    intp->fwd_irq->index = intp->pin;
+    intp->fwd_irq->gsi = intp->virtualID;
+
+    attr.addr = (uint64_t)(unsigned long)intp->fwd_irq;
+
+    if (ioctl(vfio_kvm_device_fd, KVM_SET_DEVICE_ATTR, &attr)) {
+            error_report("Failed to forward IRQ %d through KVM VFIO device",
+                         intp->pin);
+            g_free(intp->fwd_irq);
+            return -errno;
+    }
+    trace_vfio_start_fwd_injection(intp->pin);
+
+    return ret;
+}
+
+#endif
+
+/*
  * Functions used for irqfd
  */
 
@@ -288,6 +334,11 @@ static int vfio_start_irqfd_injection(VFIOINTp *intp)
         .flags = KVM_IRQFD_FLAG_RESAMPLE,
     };
 
+    if (has_kvm_vfio_forward_capability() &&
+                 intp->vdev->forward_allowed) {
+        vfio_set_forwarding(intp);
+    }
+
     if (kvm_vm_ioctl(kvm_state, KVM_IRQFD, &irqfd)) {
         error_report("vfio: Error: Failed to assign the irqfd: %m");
         goto fail_irqfd;
@@ -694,6 +745,7 @@ static Property vfio_platform_dev_properties[] = {
     DEFINE_PROP_UINT32("mmap-timeout-ms", VFIOPlatformDevice,
                        mmap_timeout, 1100),
     DEFINE_PROP_BOOL("x-irqfd", VFIOPlatformDevice, irqfd_allowed, true),
+    DEFINE_PROP_BOOL("x-forward", VFIOPlatformDevice, forward_allowed, true),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/include/hw/vfio/vfio-platform.h b/include/hw/vfio/vfio-platform.h
index de0b5d5..d512bb3 100644
--- a/include/hw/vfio/vfio-platform.h
+++ b/include/hw/vfio/vfio-platform.h
@@ -42,6 +42,7 @@ typedef struct VFIOINTp {
     bool kvm_accel; /* set when QEMU bypass through KVM enabled */
     uint8_t pin; /* index */
     uint8_t virtualID; /* virtual IRQ */
+    struct kvm_arch_forwarded_irq *fwd_irq;
 } VFIOINTp;
 
 typedef int (*start_irq_fn_t)(VFIOINTp *intp);
@@ -59,6 +60,7 @@ typedef struct VFIOPlatformDevice {
     start_irq_fn_t start_irq_fn;
     QemuMutex  intp_mutex;
     bool irqfd_allowed; /* debug option to force irqfd on/off */
+    bool forward_allowed; /* debug option to force forwarding on/off */
 } VFIOPlatformDevice;
 
 
diff --git a/trace-events b/trace-events
index 59a09f6..0aea358 100644
--- a/trace-events
+++ b/trace-events
@@ -1431,6 +1431,7 @@ vfio_get_device(const char * name, unsigned int flags, unsigned int num_regions,
 vfio_put_base_device(int fd) "close vdev->fd=%d"
 
 # hw/vfio/platform.c
+vfio_start_fwd_injection(int pin) "forwarding set for IRQ pin %d"
 vfio_platform_eoi(int pin, int fd) "EOI IRQ pin %d (fd=%d)"
 vfio_platform_mmap_set_enabled(bool enabled) "fast path = %d"
 vfio_platform_intp_mmap_enable(int pin) "IRQ #%d still active, stay in slow path"
-- 
1.8.3.2