[Qemu-devel] [PATCH] vfio-pci: Enable device request notification support

[Alex Williamson]

Linux v4.0-rc1 vfio-pci introduced a new virtual interrupt to allow
the kernel to request a device from the user.  When signaled, QEMU
will by default attmempt to hot-unplug the device.  This is a one-
shot attempt with the expectation that the kernel will continue to
poll for the device if it is not returned.  Returning the device when
requested is the expected standard model of cooperative usage, but we
also add an option option to disable this feature.  Initially this
opt-out is set as an experimental option because we really should
honor kernel requests for the device.

Signed-off-by: Alex Williamson <address@hidden>
---

This was posted as an RFC on Feb 4th, now that 4.0-rc1 is out and
includes the kernel support for this, I'm reposting as I intend to
include it in a pull request prior to the QEMU 2.3 hard freeze.  I'm
also including only a partial linux-headers update given the timing
relative to hard freeze and the number of kvm and virtio changes in
4.0-rc1 that I cannot vouch for.  If there are any objections, please
let me know.  Thanks.

 hw/vfio/pci.c              |  100 ++++++++++++++++++++++++++++++++++++++++++++
 linux-headers/linux/vfio.h |    1 
 2 files changed, 101 insertions(+)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 3c71de3..6b80539 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -153,13 +153,17 @@ typedef struct VFIOPCIDevice {
     VFIOVGA vga; /* 0xa0000, 0x3b0, 0x3c0 */
     PCIHostDeviceAddress host;
     EventNotifier err_notifier;
+    EventNotifier req_notifier;
     uint32_t features;
 #define VFIO_FEATURE_ENABLE_VGA_BIT 0
 #define VFIO_FEATURE_ENABLE_VGA (1 << VFIO_FEATURE_ENABLE_VGA_BIT)
+#define VFIO_FEATURE_ENABLE_REQ_BIT 1
+#define VFIO_FEATURE_ENABLE_REQ (1 << VFIO_FEATURE_ENABLE_REQ_BIT)
     int32_t bootindex;
     uint8_t pm_cap;
     bool has_vga;
     bool pci_aer;
+    bool req_enabled;
     bool has_flr;
     bool has_pm_reset;
     bool rom_read_failed;
@@ -3088,6 +3092,7 @@ static int vfio_populate_device(VFIOPCIDevice *vdev)
 
         vdev->has_vga = true;
     }
+
     irq_info.index = VFIO_PCI_ERR_IRQ_INDEX;
 
     ret = ioctl(vdev->vbasedev.fd, VFIO_DEVICE_GET_IRQ_INFO, &irq_info);
@@ -3223,6 +3228,97 @@ static void vfio_unregister_err_notifier(VFIOPCIDevice 
*vdev)
     event_notifier_cleanup(&vdev->err_notifier);
 }
 
+static void vfio_req_notifier_handler(void *opaque)
+{
+    VFIOPCIDevice *vdev = opaque;
+
+    if (!event_notifier_test_and_clear(&vdev->req_notifier)) {
+        return;
+    }
+
+    qdev_unplug(&vdev->pdev.qdev, NULL);
+}
+
+static void vfio_register_req_notifier(VFIOPCIDevice *vdev)
+{
+    struct vfio_irq_info irq_info = { .argsz = sizeof(irq_info),
+                                      .index = VFIO_PCI_REQ_IRQ_INDEX };
+    int argsz;
+    struct vfio_irq_set *irq_set;
+    int32_t *pfd;
+
+    if (!(vdev->features & VFIO_FEATURE_ENABLE_REQ)) {
+        return;
+    }
+
+    if (ioctl(vdev->vbasedev.fd,
+              VFIO_DEVICE_GET_IRQ_INFO, &irq_info) < 0 || irq_info.count < 1) {
+        return;
+    }
+
+    if (event_notifier_init(&vdev->req_notifier, 0)) {
+        error_report("vfio: Unable to init event notifier for device request");
+        return;
+    }
+
+    argsz = sizeof(*irq_set) + sizeof(*pfd);
+
+    irq_set = g_malloc0(argsz);
+    irq_set->argsz = argsz;
+    irq_set->flags = VFIO_IRQ_SET_DATA_EVENTFD |
+                     VFIO_IRQ_SET_ACTION_TRIGGER;
+    irq_set->index = VFIO_PCI_REQ_IRQ_INDEX;
+    irq_set->start = 0;
+    irq_set->count = 1;
+    pfd = (int32_t *)&irq_set->data;
+
+    *pfd = event_notifier_get_fd(&vdev->req_notifier);
+    qemu_set_fd_handler(*pfd, vfio_req_notifier_handler, NULL, vdev);
+
+    if (ioctl(vdev->vbasedev.fd, VFIO_DEVICE_SET_IRQS, irq_set)) {
+        error_report("vfio: Failed to set up device request notification");
+        qemu_set_fd_handler(*pfd, NULL, NULL, vdev);
+        event_notifier_cleanup(&vdev->req_notifier);
+    } else {
+        vdev->req_enabled = true;
+    }
+
+    g_free(irq_set);
+}
+
+static void vfio_unregister_req_notifier(VFIOPCIDevice *vdev)
+{
+    int argsz;
+    struct vfio_irq_set *irq_set;
+    int32_t *pfd;
+
+    if (!vdev->req_enabled) {
+        return;
+    }
+
+    argsz = sizeof(*irq_set) + sizeof(*pfd);
+
+    irq_set = g_malloc0(argsz);
+    irq_set->argsz = argsz;
+    irq_set->flags = VFIO_IRQ_SET_DATA_EVENTFD |
+                     VFIO_IRQ_SET_ACTION_TRIGGER;
+    irq_set->index = VFIO_PCI_REQ_IRQ_INDEX;
+    irq_set->start = 0;
+    irq_set->count = 1;
+    pfd = (int32_t *)&irq_set->data;
+    *pfd = -1;
+
+    if (ioctl(vdev->vbasedev.fd, VFIO_DEVICE_SET_IRQS, irq_set)) {
+        error_report("vfio: Failed to de-assign device request fd: %m");
+    }
+    g_free(irq_set);
+    qemu_set_fd_handler(event_notifier_get_fd(&vdev->req_notifier),
+                        NULL, NULL, vdev);
+    event_notifier_cleanup(&vdev->req_notifier);
+
+    vdev->req_enabled = false;
+}
+
 static int vfio_initfn(PCIDevice *pdev)
 {
     VFIOPCIDevice *vdev = DO_UPCAST(VFIOPCIDevice, pdev, pdev);
@@ -3370,6 +3466,7 @@ static int vfio_initfn(PCIDevice *pdev)
     }
 
     vfio_register_err_notifier(vdev);
+    vfio_register_req_notifier(vdev);
 
     return 0;
 
@@ -3397,6 +3494,7 @@ static void vfio_exitfn(PCIDevice *pdev)
 {
     VFIOPCIDevice *vdev = DO_UPCAST(VFIOPCIDevice, pdev, pdev);
 
+    vfio_unregister_req_notifier(vdev);
     vfio_unregister_err_notifier(vdev);
     pci_device_set_intx_routing_notifier(&vdev->pdev, NULL);
     vfio_disable_interrupts(vdev);
@@ -3455,6 +3553,8 @@ static Property vfio_pci_dev_properties[] = {
                        intx.mmap_timeout, 1100),
     DEFINE_PROP_BIT("x-vga", VFIOPCIDevice, features,
                     VFIO_FEATURE_ENABLE_VGA_BIT, false),
+    DEFINE_PROP_BIT("x-req", VFIOPCIDevice, features,
+                    VFIO_FEATURE_ENABLE_REQ_BIT, true),
     DEFINE_PROP_INT32("bootindex", VFIOPCIDevice, bootindex, -1),
     DEFINE_PROP_BOOL("x-mmap", VFIOPCIDevice, vbasedev.allow_mmap, true),
     /*
diff --git a/linux-headers/linux/vfio.h b/linux-headers/linux/vfio.h
index 0f21aa6..95ba870 100644
--- a/linux-headers/linux/vfio.h
+++ b/linux-headers/linux/vfio.h
@@ -333,6 +333,7 @@ enum {
        VFIO_PCI_MSI_IRQ_INDEX,
        VFIO_PCI_MSIX_IRQ_INDEX,
        VFIO_PCI_ERR_IRQ_INDEX,
+       VFIO_PCI_REQ_IRQ_INDEX,
        VFIO_PCI_NUM_IRQS
 };