virtio-pci: introduce pio notification capability for modern device

We used to use mmio for notification. This could be slow on some arch
(e.g on x86 without EPT). So this patch introduces pio bar and a pio
notification cap for modern device. This ability is enabled through
property "modern-pio-notify" for virtio pci devices and was disabled
by default. Management can enable when it thinks it was needed.

Benchmarks shows almost no obvious difference compared to legacy
device on machines without ept. Thanks Wenli Quan <wquan@redhat.com>
for the benchmarking.

Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 105 insertions, 17 deletions

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 9c3f6e30d7..e4449daeb9 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -271,7 +271,9 @@ static int virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
     bool legacy = !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_LEGACY);
     bool modern = !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_MODERN);
     bool fast_mmio = kvm_ioeventfd_any_length_enabled();
+    bool modern_pio = proxy->flags & VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY;
     MemoryRegion *modern_mr = &proxy->notify.mr;
+    MemoryRegion *modern_notify_mr = &proxy->notify_pio.mr;
     MemoryRegion *legacy_mr = &proxy->bar;
     hwaddr modern_addr = QEMU_VIRTIO_PCI_QUEUE_MEM_MULT *
                          virtio_get_queue_index(vq);
@@ -294,6 +296,10 @@ static int virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
                 memory_region_add_eventfd(modern_mr, modern_addr, 2,
                                           false, n, notifier);
             }
+            if (modern_pio) {
+                memory_region_add_eventfd(modern_notify_mr, 0, 2,
+                                              true, n, notifier);
+            }
         }
         if (legacy) {
             memory_region_add_eventfd(legacy_mr, legacy_addr, 2,
@@ -308,6 +314,10 @@ static int virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
                 memory_region_del_eventfd(modern_mr, modern_addr, 2,
                                           false, n, notifier);
             }
+            if (modern_pio) {
+                memory_region_del_eventfd(modern_notify_mr, 0, 2,
+                                          true, n, notifier);
+            }
         }
         if (legacy) {
             memory_region_del_eventfd(legacy_mr, legacy_addr, 2,
@@ -1416,6 +1426,17 @@ static void virtio_pci_notify_write(void *opaque, hwaddr addr,
     }
 }
 
+static void virtio_pci_notify_write_pio(void *opaque, hwaddr addr,
+                                        uint64_t val, unsigned size)
+{
+    VirtIODevice *vdev = opaque;
+    unsigned queue = val;
+
+    if (queue < VIRTIO_QUEUE_MAX) {
+        virtio_queue_notify(vdev, queue);
+    }
+}
+
 static uint64_t virtio_pci_isr_read(void *opaque, hwaddr addr,
                                     unsigned size)
 {
@@ -1509,6 +1530,16 @@ static void virtio_pci_modern_regions_init(VirtIOPCIProxy *proxy)
         },
         .endianness = DEVICE_LITTLE_ENDIAN,
     };
+    static const MemoryRegionOps notify_pio_ops = {
+        .read = virtio_pci_notify_read,
+        .write = virtio_pci_notify_write_pio,
+        .impl = {
+            .min_access_size = 1,
+            .max_access_size = 4,
+        },
+        .endianness = DEVICE_LITTLE_ENDIAN,
+    };
+
 
     memory_region_init_io(&proxy->common.mr, OBJECT(proxy),
                           &common_ops,
@@ -1533,30 +1564,60 @@ static void virtio_pci_modern_regions_init(VirtIOPCIProxy *proxy)
                           virtio_bus_get_device(&proxy->bus),
                           "virtio-pci-notify",
                           proxy->notify.size);
+
+    memory_region_init_io(&proxy->notify_pio.mr, OBJECT(proxy),
+                          &notify_pio_ops,
+                          virtio_bus_get_device(&proxy->bus),
+                          "virtio-pci-notify-pio",
+                          proxy->notify.size);
 }
 
 static void virtio_pci_modern_region_map(VirtIOPCIProxy *proxy,
                                          VirtIOPCIRegion *region,
-                                         struct virtio_pci_cap *cap)
+                                         struct virtio_pci_cap *cap,
+                                         MemoryRegion *mr,
+                                         uint8_t bar)
 {
-    memory_region_add_subregion(&proxy->modern_bar,
-                                region->offset,
-                                &region->mr);
+    memory_region_add_subregion(mr, region->offset, &region->mr);
 
     cap->cfg_type = region->type;
-    cap->bar = proxy->modern_mem_bar;
+    cap->bar = bar;
     cap->offset = cpu_to_le32(region->offset);
     cap->length = cpu_to_le32(region->size);
     virtio_pci_add_mem_cap(proxy, cap);
+
+}
+
+static void virtio_pci_modern_mem_region_map(VirtIOPCIProxy *proxy,
+                                             VirtIOPCIRegion *region,
+                                             struct virtio_pci_cap *cap)
+{
+    virtio_pci_modern_region_map(proxy, region, cap,
+                                 &proxy->modern_bar, proxy->modern_mem_bar);
 }
 
-static void virtio_pci_modern_region_unmap(VirtIOPCIProxy *proxy,
-                                           VirtIOPCIRegion *region)
+static void virtio_pci_modern_io_region_map(VirtIOPCIProxy *proxy,
+                                            VirtIOPCIRegion *region,
+                                            struct virtio_pci_cap *cap)
+{
+    virtio_pci_modern_region_map(proxy, region, cap,
+                                 &proxy->io_bar, proxy->modern_io_bar);
+}
+
+static void virtio_pci_modern_mem_region_unmap(VirtIOPCIProxy *proxy,
+                                               VirtIOPCIRegion *region)
 {
     memory_region_del_subregion(&proxy->modern_bar,
                                 &region->mr);
 }
 
+static void virtio_pci_modern_io_region_unmap(VirtIOPCIProxy *proxy,
+                                              VirtIOPCIRegion *region)
+{
+    memory_region_del_subregion(&proxy->io_bar,
+                                &region->mr);
+}
+
 /* This is called by virtio-bus just after the device is plugged. */
 static void virtio_pci_device_plugged(DeviceState *d, Error **errp)
 {
@@ -1564,6 +1625,7 @@ static void virtio_pci_device_plugged(DeviceState *d, Error **errp)
     VirtioBusState *bus = &proxy->bus;
     bool legacy = !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_LEGACY);
     bool modern = !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_MODERN);
+    bool modern_pio = proxy->flags & VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY;
     uint8_t *config;
     uint32_t size;
     VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
@@ -1602,16 +1664,31 @@ static void virtio_pci_device_plugged(DeviceState *d, Error **errp)
             .cap.cap_len = sizeof cfg,
             .cap.cfg_type = VIRTIO_PCI_CAP_PCI_CFG,
         };
-        struct virtio_pci_cfg_cap *cfg_mask;
+        struct virtio_pci_notify_cap notify_pio = {
+            .cap.cap_len = sizeof notify,
+            .notify_off_multiplier = cpu_to_le32(0x0),
+        };
 
-        /* TODO: add io access for speed */
+        struct virtio_pci_cfg_cap *cfg_mask;
 
         virtio_add_feature(&vdev->host_features, VIRTIO_F_VERSION_1);
         virtio_pci_modern_regions_init(proxy);
-        virtio_pci_modern_region_map(proxy, &proxy->common, &cap);
-        virtio_pci_modern_region_map(proxy, &proxy->isr, &cap);
-        virtio_pci_modern_region_map(proxy, &proxy->device, &cap);
-        virtio_pci_modern_region_map(proxy, &proxy->notify, &notify.cap);
+
+        virtio_pci_modern_mem_region_map(proxy, &proxy->common, &cap);
+        virtio_pci_modern_mem_region_map(proxy, &proxy->isr, &cap);
+        virtio_pci_modern_mem_region_map(proxy, &proxy->device, &cap);
+        virtio_pci_modern_mem_region_map(proxy, &proxy->notify, &notify.cap);
+
+        if (modern_pio) {
+            memory_region_init(&proxy->io_bar, OBJECT(proxy),
+                               "virtio-pci-io", 0x4);
+
+            pci_register_bar(&proxy->pci_dev, proxy->modern_io_bar,
+                             PCI_BASE_ADDRESS_SPACE_IO, &proxy->io_bar);
+
+            virtio_pci_modern_io_region_map(proxy, &proxy->notify_pio,
+                                            &notify_pio.cap);
+        }
 
         pci_register_bar(&proxy->pci_dev, proxy->modern_mem_bar,
                          PCI_BASE_ADDRESS_SPACE_MEMORY |
@@ -1667,14 +1744,18 @@ static void virtio_pci_device_unplugged(DeviceState *d)
 {
     VirtIOPCIProxy *proxy = VIRTIO_PCI(d);
     bool modern = !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_MODERN);
+    bool modern_pio = proxy->flags & VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY;
 
     virtio_pci_stop_ioeventfd(proxy);
 
     if (modern) {
-        virtio_pci_modern_region_unmap(proxy, &proxy->common);
-        virtio_pci_modern_region_unmap(proxy, &proxy->isr);
-        virtio_pci_modern_region_unmap(proxy, &proxy->device);
-        virtio_pci_modern_region_unmap(proxy, &proxy->notify);
+        virtio_pci_modern_mem_region_unmap(proxy, &proxy->common);
+        virtio_pci_modern_mem_region_unmap(proxy, &proxy->isr);
+        virtio_pci_modern_mem_region_unmap(proxy, &proxy->device);
+        virtio_pci_modern_mem_region_unmap(proxy, &proxy->notify);
+        if (modern_pio) {
+            virtio_pci_modern_io_region_unmap(proxy, &proxy->notify_pio);
+        }
     }
 }
 
@@ -1694,6 +1775,7 @@ static void virtio_pci_realize(PCIDevice *pci_dev, Error **errp)
      */
     proxy->legacy_io_bar  = 0;
     proxy->msix_bar       = 1;
+    proxy->modern_io_bar  = 2;
     proxy->modern_mem_bar = 4;
 
     proxy->common.offset = 0x0;
@@ -1713,6 +1795,10 @@ static void virtio_pci_realize(PCIDevice *pci_dev, Error **errp)
         QEMU_VIRTIO_PCI_QUEUE_MEM_MULT * VIRTIO_QUEUE_MAX;
     proxy->notify.type = VIRTIO_PCI_CAP_NOTIFY_CFG;
 
+    proxy->notify_pio.offset = 0x0;
+    proxy->notify_pio.size = 0x4;
+    proxy->notify_pio.type = VIRTIO_PCI_CAP_NOTIFY_CFG;
+
     /* subclasses can enforce modern, so do this unconditionally */
     memory_region_init(&proxy->modern_bar, OBJECT(proxy), "virtio-pci",
                        2 * QEMU_VIRTIO_PCI_QUEUE_MEM_MULT *
@@ -1759,6 +1845,8 @@ static Property virtio_pci_properties[] = {
                     VIRTIO_PCI_FLAG_DISABLE_MODERN_BIT, true),
     DEFINE_PROP_BIT("migrate-extra", VirtIOPCIProxy, flags,
                     VIRTIO_PCI_FLAG_MIGRATE_EXTRA_BIT, true),
+    DEFINE_PROP_BIT("modern-pio-notify", VirtIOPCIProxy, flags,
+                    VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY_BIT, false),
     DEFINE_PROP_END_OF_LIST(),
 };