vfio: mark posted writes in region write callbacks

For vfio-user, the region write implementation needs to know if the
write is posted; add the necessary plumbing to support this.

Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250607001056.335310-5-john.levon@nutanix.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio/device.c

@@ -543,7 +543,8 @@ static int vfio_device_io_region_read(VFIODevice *vbasedev, uint8_t index,
 }
 
 static int vfio_device_io_region_write(VFIODevice *vbasedev, uint8_t index,
-                                       off_t off, uint32_t size, void *data)
+                                       off_t off, uint32_t size, void *data,
+                                       bool post)
 {
     struct vfio_region_info *info;
     int ret;

hw/vfio/pci.c

@@ -989,7 +989,7 @@ static int vfio_pci_config_space_write(VFIOPCIDevice *vdev, off_t offset,
 {
     return vdev->vbasedev.io_ops->region_write(&vdev->vbasedev,
                                                VFIO_PCI_CONFIG_REGION_INDEX,
-                                               offset, size, data);
+                                               offset, size, data, false);
 }
 
 static uint64_t vfio_rom_read(void *opaque, hwaddr addr, unsigned size)
@@ -1793,6 +1793,9 @@ static void vfio_bar_prepare(VFIOPCIDevice *vdev, int nr)
     bar->type = pci_bar & (bar->ioport ? ~PCI_BASE_ADDRESS_IO_MASK :
                                          ~PCI_BASE_ADDRESS_MEM_MASK);
     bar->size = bar->region.size;
+
+    /* IO regions are sync, memory can be async */
+    bar->region.post_wr = (bar->ioport == 0);
 }
 
 static void vfio_bars_prepare(VFIOPCIDevice *vdev)

hw/vfio/region.c

@@ -66,7 +66,7 @@ void vfio_region_write(void *opaque, hwaddr addr,
     }
 
     ret = vbasedev->io_ops->region_write(vbasedev, region->nr,
-                                         addr, size, &buf);
+                                         addr, size, &buf, region->post_wr);
     if (ret != size) {
         error_report("%s(%s:region%d+0x%"HWADDR_PRIx", 0x%"PRIx64
                      ",%d) failed: %s",
@@ -200,6 +200,7 @@ int vfio_region_setup(Object *obj, VFIODevice *vbasedev, VFIORegion *region,
     region->size = info->size;
     region->fd_offset = info->offset;
     region->nr = index;
+    region->post_wr = false;
 
     if (region->size) {
         region->mem = g_new0(MemoryRegion, 1);

include/hw/vfio/vfio-device.h

@@ -205,10 +205,10 @@ struct VFIODeviceIOOps {
      * @region_write
      *
      * Write @size bytes to the region @nr at offset @off from the buffer
-     * @data.
+     * @data; if @post, the write is posted.
      */
     int (*region_write)(VFIODevice *vdev, uint8_t nr, off_t off, uint32_t size,
-                        void *data);
+                        void *data, bool post);
 };
 
 void vfio_device_prepare(VFIODevice *vbasedev, VFIOContainerBase *bcontainer,

include/hw/vfio/vfio-region.h

@@ -29,6 +29,7 @@ typedef struct VFIORegion {
     uint32_t nr_mmaps;
     VFIOMmap *mmaps;
     uint8_t nr; /* cache the region number for debug */
+    bool post_wr; /* writes can be posted */
 } VFIORegion;