Re: [PATCH v2 08/29] vfio: mark posted writes in region write callbacks

[Cédric Le Goater]

On 5/20/25 17:03, John Levon wrote:

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.le...@nutanix.com>

Reviewed-by: Cédric Le Goater <c...@redhat.com>

Thanks,

C.

---
  include/hw/vfio/vfio-device.h | 4 ++--
  include/hw/vfio/vfio-region.h | 1 +
  hw/vfio/device.c              | 3 ++-
  hw/vfio/pci.c                 | 5 ++++-
  hw/vfio/region.c              | 3 ++-
  5 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/include/hw/vfio/vfio-device.h b/include/hw/vfio/vfio-device.h
index 5cb817fd6a..a23ef4ea13 100644
--- a/include/hw/vfio/vfio-device.h
+++ b/include/hw/vfio/vfio-device.h
@@ -207,10 +207,10 @@ 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,

diff --git a/include/hw/vfio/vfio-region.h b/include/hw/vfio/vfio-region.h
index 80e83b23fd..f1ae5125ba 100644
--- a/include/hw/vfio/vfio-region.h
+++ b/include/hw/vfio/vfio-region.h
@@ -30,6 +30,7 @@ typedef struct VFIORegion {
      VFIOMmap *mmaps;
      uint8_t nr; /* cache the region number for debug */
      int fd; /* fd to mmap() region */
+    bool post_wr; /* writes can be posted */
  } VFIORegion;

diff --git a/hw/vfio/device.c b/hw/vfio/device.c

index 41db403992..cb1a212b8f 100644
--- a/hw/vfio/device.c
+++ b/hw/vfio/device.c
@@ -572,7 +572,8 @@ 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;
diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index ef38b4692a..3d1dbdac38 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -1016,7 +1016,7 @@ 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)

@@ -1820,6 +1820,9 @@ 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)

diff --git a/hw/vfio/region.c b/hw/vfio/region.c
index 3c93da91d8..936502b37a 100644
--- a/hw/vfio/region.c
+++ b/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 (vbasedev->region_fds != NULL) {
          region->fd = vbasedev->region_fds[index];
      } else {