Re: [RFC v3 11/19] vfio-user: get region info

[Alex Williamson]

On Mon,  8 Nov 2021 16:46:39 -0800
John Johnson <john.g.johnson@oracle.com> wrote:

> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> ---
>  hw/vfio/user-protocol.h       | 14 ++++++++++++
>  include/hw/vfio/vfio-common.h |  4 +++-
>  hw/vfio/common.c              | 30 +++++++++++++++++++++++++-
>  hw/vfio/user.c                | 50 
> +++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 96 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/vfio/user-protocol.h b/hw/vfio/user-protocol.h
> index 13e44eb..104bf4f 100644
> --- a/hw/vfio/user-protocol.h
> +++ b/hw/vfio/user-protocol.h
> @@ -95,4 +95,18 @@ typedef struct {
>      uint32_t cap_offset;
>  } VFIOUserDeviceInfo;
>  
> +/*
> + * VFIO_USER_DEVICE_GET_REGION_INFO
> + * imported from struct_vfio_region_info
> + */
> +typedef struct {
> +    VFIOUserHdr hdr;
> +    uint32_t argsz;
> +    uint32_t flags;
> +    uint32_t index;
> +    uint32_t cap_offset;
> +    uint64_t size;
> +    uint64_t offset;
> +} VFIOUserRegionInfo;
> +
>  #endif /* VFIO_USER_PROTOCOL_H */
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index 224dbf8..e2d7ee1 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -56,6 +56,7 @@ typedef struct VFIORegion {
>      uint32_t nr_mmaps;
>      VFIOMmap *mmaps;
>      uint8_t nr; /* cache the region number for debug */
> +    int remfd; /* fd if exported from remote process */
>  } VFIORegion;
>  
>  typedef struct VFIOMigration {
> @@ -150,8 +151,9 @@ typedef struct VFIODevice {
>      VFIOMigration *migration;
>      Error *migration_blocker;
>      OnOffAuto pre_copy_dirty_page_tracking;
> -    struct vfio_region_info **regions;
>      VFIOProxy *proxy;
> +    struct vfio_region_info **regions;
> +    int *regfds;
>  } VFIODevice;
>  
>  struct VFIODeviceOps {
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 41fdd78..47ec28f 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -40,6 +40,7 @@
>  #include "trace.h"
>  #include "qapi/error.h"
>  #include "migration/migration.h"
> +#include "hw/vfio/user.h"
>  
>  VFIOGroupList vfio_group_list =
>      QLIST_HEAD_INITIALIZER(vfio_group_list);
> @@ -1491,6 +1492,16 @@ bool vfio_get_info_dma_avail(struct 
> vfio_iommu_type1_info *info,
>      return true;
>  }
>  
> +static int vfio_get_region_info_remfd(VFIODevice *vbasedev, int index)
> +{
> +    struct vfio_region_info *info;
> +
> +    if (vbasedev->regions == NULL || vbasedev->regions[index] == NULL) {
> +        vfio_get_region_info(vbasedev, index, &info);
> +    }
> +    return vbasedev->regfds != NULL ? vbasedev->regfds[index] : -1;
> +}

This patch is really obscure due to the region info fd being added many
patches ago and only now being used.

Do we really want a parallel array to regions for storing these fds?

Why do we call an array of these fds "regfds" but a single one "remfd"?

Ugh, why do we have both the regfds array and a remfd per VFIORegion?

TBH, I'm still not sure why we're caching region infos at all, this
seems to be gratuitously bloated.

> +
>  static int vfio_setup_region_sparse_mmaps(VFIORegion *region,
>                                            struct vfio_region_info *info)
>  {
> @@ -1544,6 +1555,7 @@ int vfio_region_setup(Object *obj, VFIODevice 
> *vbasedev, VFIORegion *region,
>      region->size = info->size;
>      region->fd_offset = info->offset;
>      region->nr = index;
> +    region->remfd = vfio_get_region_info_remfd(vbasedev, index);

Why didn't we just get an fd back from vfio_get_region_info() that we
could use here?

>  
>      if (region->size) {
>          region->mem = g_new0(MemoryRegion, 1);
> @@ -1587,6 +1599,7 @@ int vfio_region_mmap(VFIORegion *region)
>  {
>      int i, prot = 0;
>      char *name;
> +    int fd;
>  
>      if (!region->mem) {
>          return 0;
> @@ -1595,9 +1608,11 @@ int vfio_region_mmap(VFIORegion *region)
>      prot |= region->flags & VFIO_REGION_INFO_FLAG_READ ? PROT_READ : 0;
>      prot |= region->flags & VFIO_REGION_INFO_FLAG_WRITE ? PROT_WRITE : 0;
>  
> +    fd = region->remfd != -1 ? region->remfd : region->vbasedev->fd;

Gack, why can't VFIORegion.fd be either the remote process fd or the
vbasedevfd to avoid all these switches?  Thanks,

Alex

> +
>      for (i = 0; i < region->nr_mmaps; i++) {
>          region->mmaps[i].mmap = mmap(NULL, region->mmaps[i].size, prot,
> -                                     MAP_SHARED, region->vbasedev->fd,
> +                                     MAP_SHARED, fd,
>                                       region->fd_offset +
>                                       region->mmaps[i].offset);
>          if (region->mmaps[i].mmap == MAP_FAILED) {
> @@ -2379,10 +2394,17 @@ void vfio_put_base_device(VFIODevice *vbasedev)
>          int i;
>  
>          for (i = 0; i < vbasedev->num_regions; i++) {
> +            if (vbasedev->regfds != NULL && vbasedev->regfds[i] != -1) {
> +                close(vbasedev->regfds[i]);
> +            }
>              g_free(vbasedev->regions[i]);
>          }
>          g_free(vbasedev->regions);
>          vbasedev->regions = NULL;
> +        if (vbasedev->regfds != NULL) {
> +            g_free(vbasedev->regfds);
> +            vbasedev->regfds = NULL;
> +        }
>      }
>  
>      if (!vbasedev->group) {
> @@ -2405,6 +2427,9 @@ int vfio_get_region_info(VFIODevice *vbasedev, int 
> index,
>      if (vbasedev->regions == NULL) {
>          vbasedev->regions = g_new0(struct vfio_region_info *,
>                                     vbasedev->num_regions);
> +        if (vbasedev->proxy != NULL) {
> +            vbasedev->regfds = g_new0(int, vbasedev->num_regions);
> +        }
>      }
>      /* check cache */
>      if (vbasedev->regions[index] != NULL) {
> @@ -2441,6 +2466,9 @@ retry:
>      /* fill cache */
>      vbasedev->regions[index] = g_malloc0(argsz);
>      memcpy(vbasedev->regions[index], *info, argsz);
> +    if (vbasedev->regfds != NULL) {
> +        vbasedev->regfds[index] = fd;
> +    }
>  
>      return 0;
>  }
> diff --git a/hw/vfio/user.c b/hw/vfio/user.c
> index ed2a4d7..b40c4ed 100644
> --- a/hw/vfio/user.c
> +++ b/hw/vfio/user.c
> @@ -923,6 +923,40 @@ static int vfio_user_get_info(VFIOProxy *proxy, struct 
> vfio_device_info *info)
>      return 0;
>  }
>  
> +static int vfio_user_get_region_info(VFIOProxy *proxy,
> +                                     struct vfio_region_info *info,
> +                                     VFIOUserFDs *fds)
> +{
> +    g_autofree VFIOUserRegionInfo *msgp = NULL;
> +    uint32_t size;
> +
> +    /* data returned can be larger than vfio_region_info */
> +    if (info->argsz < sizeof(*info)) {
> +        error_printf("vfio_user_get_region_info argsz too small\n");
> +        return -EINVAL;
> +    }
> +    if (fds != NULL && fds->send_fds != 0) {
> +        error_printf("vfio_user_get_region_info can't send FDs\n");
> +        return -EINVAL;
> +    }
> +
> +    size = info->argsz + sizeof(VFIOUserHdr);
> +    msgp = g_malloc0(size);
> +
> +    vfio_user_request_msg(&msgp->hdr, VFIO_USER_DEVICE_GET_REGION_INFO,
> +                          sizeof(*msgp), 0);
> +    msgp->argsz = info->argsz;
> +    msgp->index = info->index;
> +
> +    vfio_user_send_wait(proxy, &msgp->hdr, fds, size, false);
> +    if (msgp->hdr.flags & VFIO_USER_ERROR) {
> +        return -msgp->hdr.error_reply;
> +    }
> +
> +    memcpy(info, &msgp->argsz, info->argsz);
> +    return 0;
> +}
> +
>  
>  /*
>   * Socket-based io_ops
> @@ -941,7 +975,23 @@ static int vfio_user_io_get_info(VFIODevice *vbasedev,
>      return VDEV_VALID_INFO(vbasedev, info);
>  }
>  
> +static int vfio_user_io_get_region_info(VFIODevice *vbasedev,
> +                                        struct vfio_region_info *info,
> +                                        int *fd)
> +{
> +    int ret;
> +    VFIOUserFDs fds = { 0, 1, fd};
> +
> +    ret = vfio_user_get_region_info(vbasedev->proxy, info, &fds);
> +    if (ret) {
> +        return ret;
> +    }
> +
> +    return VDEV_VALID_REGION_INFO(vbasedev, info, fd);
> +}
> +
>  VFIODevIO vfio_dev_io_sock = {
>      .get_info = vfio_user_io_get_info,
> +    .get_region_info = vfio_user_io_get_region_info,
>  };
>