Re: [PATCH v5 11/11] vfio: Disable only uncoordinated discards for VFIO_TYPE1 iommus

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 21 Jan 2021 12:05:40 +0100
David Hildenbrand <david@redhat.com> wrote:

> We support coordinated discarding of RAM using the RamDiscardMgr for
> the VFIO_TYPE1 iommus. Let's unlock support for coordinated discards,
> keeping uncoordinated discards (e.g., via virtio-balloon) disabled if
> possible.
> 
> This unlocks virtio-mem + vfio on x86-64. Note that vfio used via "nvme://"
> by the block layer has to be implemented/unlocked separately. For now,
> virtio-mem only supports x86-64; we don't restrict RamDiscardMgr to x86-64,
> though: arm64 and s390x are supposed to work as well, and we'll test
> once unlocking virtio-mem support. The spapr IOMMUs will need special
> care, to be tackled later, e.g.., once supporting virtio-mem.
> 
> Note: The block size of a virtio-mem device has to be set to sane sizes,
> depending on the maximum hotplug size - to not run out of vfio mappings.
> The default virtio-mem block size is usually in the range of a couple of
> MBs. The maximum number of mapping is 64k, shared with other users.
> Assume you want to hotplug 256GB using virtio-mem - the block size would
> have to be set to at least 8 MiB (resulting in 32768 separate mappings).
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Auger Eric <eric.auger@redhat.com>
> Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
> Cc: teawater <teawaterz@linux.alibaba.com>
> Cc: Marek Kedzierski <mkedzier@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  hw/vfio/common.c | 63 +++++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 51 insertions(+), 12 deletions(-)


Acked-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>


> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 15ecd05a4b..d879b8ab92 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -135,6 +135,27 @@ static const char *index_to_str(VFIODevice *vbasedev, int index)
>      }
>  }
>  
> +static int vfio_ram_block_discard_disable(VFIOContainer *container, bool state)
> +{
> +    switch (container->iommu_type) {
> +    case VFIO_TYPE1v2_IOMMU:
> +    case VFIO_TYPE1_IOMMU:
> +        /* We support coordinated discarding of RAM via the RamDiscardMgr. */
> +        return ram_block_uncoordinated_discard_disable(state);
> +    default:
> +        /*
> +         * VFIO_SPAPR_TCE_IOMMU most probably works just fine with
> +         * RamDiscardMgr, however, it is completely untested.
> +         *
> +         * VFIO_SPAPR_TCE_v2_IOMMU with "DMA memory preregistering" does
> +         * completely the opposite of managing mapping/pinning dynamically as
> +         * required by RamDiscardMgr. We would have to special-case sections
> +         * with a RamDiscardMgr.
> +         */
> +        return ram_block_discard_disable(state);
> +    }
> +}
> +
>  int vfio_set_irq_signaling(VFIODevice *vbasedev, int index, int subindex,
>                             int action, int fd, Error **errp)
>  {
> @@ -1979,15 +2000,25 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as,
>       * new memory, it will not yet set ram_block_discard_set_required() and
>       * therefore, neither stops us here or deals with the sudden memory
>       * consumption of inflated memory.
> +     *
> +     * We do support discarding of memory coordinated via the RamDiscardMgr
> +     * with some IOMMU types. vfio_ram_block_discard_disable() handles the
> +     * details once we know which type of IOMMU we are using.
>       */
> -    ret = ram_block_discard_disable(true);
> -    if (ret) {
> -        error_setg_errno(errp, -ret, "Cannot set discarding of RAM broken");
> -        return ret;
> -    }
>  
>      QLIST_FOREACH(container, &space->containers, next) {
>          if (!ioctl(group->fd, VFIO_GROUP_SET_CONTAINER, &container->fd)) {
> +            ret = vfio_ram_block_discard_disable(container, true);
> +            if (ret) {
> +                error_setg_errno(errp, -ret,
> +                                 "Cannot set discarding of RAM broken");
> +                if (ioctl(group->fd, VFIO_GROUP_UNSET_CONTAINER,
> +                          &container->fd)) {
> +                    error_report("vfio: error disconnecting group %d from"
> +                                 " container", group->groupid);
> +                }
> +                return ret;
> +            }
>              group->container = container;
>              QLIST_INSERT_HEAD(&container->group_list, group, container_next);
>              vfio_kvm_device_add_group(group);
> @@ -2025,6 +2056,12 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as,
>          goto free_container_exit;
>      }
>  
> +    ret = vfio_ram_block_discard_disable(container, true);
> +    if (ret) {
> +        error_setg_errno(errp, -ret, "Cannot set discarding of RAM broken");
> +        goto free_container_exit;
> +    }
> +
>      switch (container->iommu_type) {
>      case VFIO_TYPE1v2_IOMMU:
>      case VFIO_TYPE1_IOMMU:
> @@ -2072,7 +2109,7 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as,
>              if (ret) {
>                  error_setg_errno(errp, errno, "failed to enable container");
>                  ret = -errno;
> -                goto free_container_exit;
> +                goto enable_discards_exit;
>              }
>          } else {
>              container->prereg_listener = vfio_prereg_listener;
> @@ -2084,7 +2121,7 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as,
>                  ret = -1;
>                  error_propagate_prepend(errp, container->error,
>                      "RAM memory listener initialization failed: ");
> -                goto free_container_exit;
> +                goto enable_discards_exit;
>              }
>          }
>  
> @@ -2097,7 +2134,7 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as,
>              if (v2) {
>                  memory_listener_unregister(&container->prereg_listener);
>              }
> -            goto free_container_exit;
> +            goto enable_discards_exit;
>          }
>  
>          if (v2) {
> @@ -2112,7 +2149,7 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as,
>              if (ret) {
>                  error_setg_errno(errp, -ret,
>                                   "failed to remove existing window");
> -                goto free_container_exit;
> +                goto enable_discards_exit;
>              }
>          } else {
>              /* The default table uses 4K pages */
> @@ -2153,6 +2190,9 @@ listener_release_exit:
>      vfio_kvm_device_del_group(group);
>      vfio_listener_release(container);
>  
> +enable_discards_exit:
> +    vfio_ram_block_discard_disable(container, false);
> +
>  free_container_exit:
>      g_free(container);
>  
> @@ -2160,7 +2200,6 @@ close_fd_exit:
>      close(fd);
>  
>  put_space_exit:
> -    ram_block_discard_disable(false);
>      vfio_put_address_space(space);
>  
>      return ret;
> @@ -2282,7 +2321,7 @@ void vfio_put_group(VFIOGroup *group)
>      }
>  
>      if (!group->ram_block_discard_allowed) {
> -        ram_block_discard_disable(false);
> +        vfio_ram_block_discard_disable(group->container, false);
>      }
>      vfio_kvm_device_del_group(group);
>      vfio_disconnect_container(group);
> @@ -2336,7 +2375,7 @@ int vfio_get_device(VFIOGroup *group, const char *name,
>  
>          if (!group->ram_block_discard_allowed) {
>              group->ram_block_discard_allowed = true;
> -            ram_block_discard_disable(false);
> +            vfio_ram_block_discard_disable(group->container, false);
>          }
>      }
>