Re: [PATCH v2 07/29] vfio: add per-region fd support

["Cédric Le Goater" <clg@redhat.com>]

On 5/20/25 17:03, John Levon wrote:
> For vfio-user, each region has its own fd rather than sharing
> vbasedev's. Add the necessary plumbing to support this. For vfio
> backends with a shared fd, initialize region->fd to the shared one.
> 
> Signed-off-by: John Levon <john.levon@nutanix.com>
> ---
>   include/hw/vfio/vfio-device.h |  7 +++++--
>   include/hw/vfio/vfio-region.h |  1 +
>   hw/vfio/device.c              | 28 ++++++++++++++++++++++++++--
>   hw/vfio/region.c              |  7 ++++++-
>   4 files changed, 38 insertions(+), 5 deletions(-)
> 
> diff --git a/include/hw/vfio/vfio-device.h b/include/hw/vfio/vfio-device.h
> index 923f9cd116..5cb817fd6a 100644
> --- a/include/hw/vfio/vfio-device.h
> +++ b/include/hw/vfio/vfio-device.h
> @@ -66,6 +66,7 @@ typedef struct VFIODevice {
>       OnOffAuto enable_migration;
>       OnOffAuto migration_multifd_transfer;
>       bool migration_events;
> +    bool use_region_fds;
>       VFIODeviceOps *ops;
>       VFIODeviceIOOps *io_ops;
>       unsigned int num_irqs;
> @@ -84,6 +85,7 @@ typedef struct VFIODevice {
>       VFIOIOASHwpt *hwpt;
>       QLIST_ENTRY(VFIODevice) hwpt_next;
>       struct vfio_region_info **reginfo;
> +    int *region_fds;
>   } VFIODevice;
>   
>   struct VFIODeviceOps {
> @@ -172,10 +174,11 @@ struct VFIODeviceIOOps {
>       /**
>        * @get_region_info
>        *
> -     * Fill in @info with information on the region given by @info->index.
> +     * Fill in @info (and optionally @fd) with information on the region given
> +     * by @info->index.

The whole VFIODeviceIOOps struct needs better documentation. The arguments
are missing.

>        */
>       int (*get_region_info)(VFIODevice *vdev,
> -                           struct vfio_region_info *info);
> +                           struct vfio_region_info *info, int *fd);
>   
>       /**
>        * @get_irq_info
> diff --git a/include/hw/vfio/vfio-region.h b/include/hw/vfio/vfio-region.h
> index cbffb26962..80e83b23fd 100644
> --- a/include/hw/vfio/vfio-region.h
> +++ b/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 */
> +    int fd; /* fd to mmap() region */

Could you split this change ? I am not sure it is needed.


>   } VFIORegion;
>   
>   
> diff --git a/hw/vfio/device.c b/hw/vfio/device.c
> index d0068086ae..41db403992 100644
> --- a/hw/vfio/device.c
> +++ b/hw/vfio/device.c
> @@ -226,6 +226,7 @@ int vfio_device_get_region_info(VFIODevice *vbasedev, int index,
>                                   struct vfio_region_info **info)
>   {
>       size_t argsz = sizeof(struct vfio_region_info);
> +    int fd = -1;
>       int ret;
>   
>       /* check cache */
> @@ -240,7 +241,7 @@ int vfio_device_get_region_info(VFIODevice *vbasedev, int index,
>   retry:
>       (*info)->argsz = argsz;
>   
> -    ret = vbasedev->io_ops->get_region_info(vbasedev, *info);
> +    ret = vbasedev->io_ops->get_region_info(vbasedev, *info, &fd);
>       if (ret != 0) {
>           g_free(*info);
>           *info = NULL;
> @@ -251,11 +252,19 @@ retry:
>           argsz = (*info)->argsz;
>           *info = g_realloc(*info, argsz);
>   
> +        if (fd != -1) {
> +            close(fd);
> +            fd = -1;
> +        }
> +
>           goto retry;
>       }
>   
>       /* fill cache */
>       vbasedev->reginfo[index] = *info;
> +    if (vbasedev->region_fds != NULL) {
> +        vbasedev->region_fds[index] = fd;
> +    }
>   
>       return 0;
>   }
> @@ -360,6 +369,7 @@ void vfio_device_init(VFIODevice *vbasedev, int type, VFIODeviceOps *ops,
>       vbasedev->io_ops = &vfio_device_io_ops_ioctl;
>       vbasedev->dev = dev;
>       vbasedev->fd = -1;
> +    vbasedev->use_region_fds = false;

I wish we could avoid this bool. I have no idea yet.


>   
>       vbasedev->ram_block_discard_allowed = ram_discard;
>   }
> @@ -470,6 +480,9 @@ void vfio_device_prepare(VFIODevice *vbasedev, VFIOContainerBase *bcontainer,
>   
>       vbasedev->reginfo = g_new0(struct vfio_region_info *,
>                                  vbasedev->num_regions);
> +    if (vbasedev->use_region_fds) {
> +        vbasedev->region_fds = g_new0(int, vbasedev->num_regions);
> +    }
>   }
>   
>   void vfio_device_unprepare(VFIODevice *vbasedev)
> @@ -478,9 +491,17 @@ void vfio_device_unprepare(VFIODevice *vbasedev)
>   
>       for (i = 0; i < vbasedev->num_regions; i++) {
>           g_free(vbasedev->reginfo[i]);
> +        if (vbasedev->region_fds != NULL && vbasedev->region_fds[i] != -1) {
> +            close(vbasedev->region_fds[i]);
> +        }
> +
>       }
>       g_free(vbasedev->reginfo);
>       vbasedev->reginfo = NULL;
> +    if (vbasedev->region_fds != NULL) {

g_free is NULL safe. No need to test for it. g_clear_pointer() is a nice
helper too.

> +        g_free(vbasedev->region_fds);
> +        vbasedev->region_fds = NULL;
> +    }
>   
>       QLIST_REMOVE(vbasedev, container_next);
>       QLIST_REMOVE(vbasedev, global_next);
> @@ -502,10 +523,13 @@ static int vfio_device_io_device_feature(VFIODevice *vbasedev,
>   }
>   
>   static int vfio_device_io_get_region_info(VFIODevice *vbasedev,
> -                                          struct vfio_region_info *info)
> +                                          struct vfio_region_info *info,
> +                                          int *fd)
>   {
>       int ret;
>   
> +    *fd = -1;
> +
>       ret = ioctl(vbasedev->fd, VFIO_DEVICE_GET_REGION_INFO, info);
>   
>       return ret < 0 ? -errno : ret;
> diff --git a/hw/vfio/region.c b/hw/vfio/region.c
> index 34752c3f65..3c93da91d8 100644
> --- a/hw/vfio/region.c
> +++ b/hw/vfio/region.c
> @@ -200,6 +200,11 @@ int vfio_region_setup(Object *obj, VFIODevice *vbasedev, VFIORegion *region,
>       region->size = info->size;
>       region->fd_offset = info->offset;
>       region->nr = index;
> +    if (vbasedev->region_fds != NULL) {
> +        region->fd = vbasedev->region_fds[index];
> +    } else {
> +        region->fd = vbasedev->fd;
> +    }
>   
>       if (region->size) {
>           region->mem = g_new0(MemoryRegion, 1);
> @@ -278,7 +283,7 @@ int vfio_region_mmap(VFIORegion *region)
>   
>           region->mmaps[i].mmap = mmap(map_align, region->mmaps[i].size, prot,
>                                        MAP_SHARED | MAP_FIXED,
> -                                     region->vbasedev->fd,
> +                                     region->fd,

Would this work ?

		vbasedev->region_fds ? vbasedev->region_fds[region->nr] : vbasedev->fd,


Thanks,

C.


>                                        region->fd_offset +
>                                        region->mmaps[i].offset);
>           if (region->mmaps[i].mmap == MAP_FAILED) {