vhost-user-blk: dynamically resize config space based on features

Make vhost-user-blk backwards compatible when migrating from older VMs
running with modern features turned off, the same way it was done for
virtio-blk in 20764be ("virtio-blk: set config size depending on the features enabled")

It's currently impossible to migrate from an older VM with
vhost-user-blk (with disable-legacy=off) because of errors like this:

qemu-system-x86_64: get_pci_config_device: Bad config data: i=0x10 read: 41 device: 1 cmask: ff wmask: 80 w1cmask:0
qemu-system-x86_64: Failed to load PCIDevice:config
qemu-system-x86_64: Failed to load virtio-blk:virtio
qemu-system-x86_64: error while loading state for instance 0x0 of device '0000:00:05.0:00.0:02.0/virtio-blk'
qemu-system-x86_64: load of migration failed: Invalid argument

This is caused by the newer (destination) VM requiring a bigger BAR0
alignment because it has to cover a bigger configuration space, which
isn't actually needed since those additional config fields are not
active (write-zeroes/discard).

Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Message-Id: <20220906073111.353245-6-d-tatianin@yandex-team.ru>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

MAINTAINERS

@@ -2281,11 +2281,13 @@ S: Maintained
 F: contrib/vhost-user-blk/
 F: contrib/vhost-user-scsi/
 F: hw/block/vhost-user-blk.c
+F: hw/block/virtio-blk-common.c
 F: hw/scsi/vhost-user-scsi.c
 F: hw/virtio/vhost-user-blk-pci.c
 F: hw/virtio/vhost-user-scsi-pci.c
 F: include/hw/virtio/vhost-user-blk.h
 F: include/hw/virtio/vhost-user-scsi.h
+F: include/hw/virtio/virtio-blk-common.h
 
 vhost-user-gpu
 M: Marc-André Lureau <marcandre.lureau@redhat.com>

hw/block/meson.build

@@ -17,6 +17,6 @@ softmmu_ss.add(when: 'CONFIG_XEN', if_true: files('xen-block.c'))
 softmmu_ss.add(when: 'CONFIG_TC58128', if_true: files('tc58128.c'))
 
 specific_ss.add(when: 'CONFIG_VIRTIO_BLK', if_true: files('virtio-blk.c', 'virtio-blk-common.c'))
-specific_ss.add(when: 'CONFIG_VHOST_USER_BLK', if_true: files('vhost-user-blk.c'))
+specific_ss.add(when: 'CONFIG_VHOST_USER_BLK', if_true: files('vhost-user-blk.c', 'virtio-blk-common.c'))
 
 subdir('dataplane')

hw/block/vhost-user-blk.c

@@ -23,6 +23,7 @@
 #include "hw/qdev-core.h"
 #include "hw/qdev-properties.h"
 #include "hw/qdev-properties-system.h"
+#include "hw/virtio/virtio-blk-common.h"
 #include "hw/virtio/vhost.h"
 #include "hw/virtio/vhost-user-blk.h"
 #include "hw/virtio/virtio.h"
@@ -63,7 +64,7 @@ static void vhost_user_blk_update_config(VirtIODevice *vdev, uint8_t *config)
     /* Our num_queues overrides the device backend */
     virtio_stw_p(vdev, &s->blkcfg.num_queues, s->num_queues);
 
-    memcpy(config, &s->blkcfg, sizeof(struct virtio_blk_config));
+    memcpy(config, &s->blkcfg, vdev->config_len);
 }
 
 static void vhost_user_blk_set_config(VirtIODevice *vdev, const uint8_t *config)
@@ -92,12 +93,12 @@ static int vhost_user_blk_handle_config_change(struct vhost_dev *dev)
 {
     int ret;
     struct virtio_blk_config blkcfg;
+    VirtIODevice *vdev = dev->vdev;
     VHostUserBlk *s = VHOST_USER_BLK(dev->vdev);
     Error *local_err = NULL;
 
     ret = vhost_dev_get_config(dev, (uint8_t *)&blkcfg,
-                               sizeof(struct virtio_blk_config),
-                               &local_err);
+                               vdev->config_len, &local_err);
     if (ret < 0) {
         error_report_err(local_err);
         return ret;
@@ -106,7 +107,7 @@ static int vhost_user_blk_handle_config_change(struct vhost_dev *dev)
     /* valid for resize only */
     if (blkcfg.capacity != s->blkcfg.capacity) {
         s->blkcfg.capacity = blkcfg.capacity;
-        memcpy(dev->vdev->config, &s->blkcfg, sizeof(struct virtio_blk_config));
+        memcpy(dev->vdev->config, &s->blkcfg, vdev->config_len);
         virtio_notify_config(dev->vdev);
     }
 
@@ -448,7 +449,7 @@ static int vhost_user_blk_realize_connect(VHostUserBlk *s, Error **errp)
     assert(s->connected);
 
     ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
-                               sizeof(struct virtio_blk_config), errp);
+                               s->parent_obj.config_len, errp);
     if (ret < 0) {
         qemu_chr_fe_disconnect(&s->chardev);
         vhost_dev_cleanup(&s->dev);
@@ -463,6 +464,7 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
     ERRP_GUARD();
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     VHostUserBlk *s = VHOST_USER_BLK(vdev);
+    size_t config_size;
     int retries;
     int i, ret;
 
@@ -493,8 +495,9 @@ static void vhost_user_blk_device_realize(DeviceState *dev, Error **errp)
         return;
     }
 
-    virtio_init(vdev, VIRTIO_ID_BLOCK,
-                sizeof(struct virtio_blk_config));
+    config_size = virtio_get_config_size(&virtio_blk_cfg_size_params,
+                                         vdev->host_features);
+    virtio_init(vdev, VIRTIO_ID_BLOCK, config_size);
 
     s->virtqs = g_new(VirtQueue *, s->num_queues);
     for (i = 0; i < s->num_queues; i++) {