Re: [PATCH v1] virtio-mem: add memory via add_memory_driver_managed()

[Pankaj Gupta]

> Virtio-mem managed memory is always detected and added by the virtio-mem
> driver, never using something like the firmware-provided memory map.
> This is the case after an ordinary system reboot, and has to be guaranteed
> after kexec. Especially, virtio-mem added memory resources can contain
> inaccessible parts ("unblocked memory blocks"), blindly forwarding them
> to a kexec kernel is dangerous, as unplugged memory will get accessed
> (esp. written).
>
> Let's use the new way of adding special driver-managed memory introduced
> in commit 75ac4c58bc0d ("mm/memory_hotplug: introduce
> add_memory_driver_managed()").

Is this commit id correct?
>
> This will result in no entries in /sys/firmware/memmap ("raw firmware-
> provided memory map"), the memory resource will be flagged
> IORESOURCE_MEM_DRIVER_MANAGED (esp., kexec_file_load() will not place
> kexec images on this memory), and it is exposed as "System RAM
> (virtio_mem)" in /proc/iomem, so esp. kexec-tools can properly handle it.
>
> Example /proc/iomem before this change:
>   [...]
>   140000000-333ffffff : virtio0
>     140000000-147ffffff : System RAM
>   334000000-533ffffff : virtio1
>     338000000-33fffffff : System RAM
>     340000000-347ffffff : System RAM
>     348000000-34fffffff : System RAM
>   [...]
>
> Example /proc/iomem after this change:
>   [...]
>   140000000-333ffffff : virtio0
>     140000000-147ffffff : System RAM (virtio_mem)
>   334000000-533ffffff : virtio1
>     338000000-33fffffff : System RAM (virtio_mem)
>     340000000-347ffffff : System RAM (virtio_mem)
>     348000000-34fffffff : System RAM (virtio_mem)
>   [...]
>
> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
> Cc: teawater <teawaterz@xxxxxxxxxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
>
> Based on latest Linus' tree (and not a tag) because
> - virtio-mem has just been merged via the vhost tree
> - add_memory_driver_managed() has been merged a week ago via the -mm tree
>
> I'd like to have this patch in 5.8, with the initial merge of virtio-mem
> if possible (so the user space representation of virtio-mem added memory
> resources won't change anymore).
>
> ---
>  drivers/virtio/virtio_mem.c | 25 ++++++++++++++++++++++---
>  1 file changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
> index 50c689f250450..d2eab3558a9e1 100644
> --- a/drivers/virtio/virtio_mem.c
> +++ b/drivers/virtio/virtio_mem.c
> @@ -101,6 +101,11 @@ struct virtio_mem {
>
>         /* The parent resource for all memory added via this device. */
>         struct resource *parent_resource;
> +       /*
> +        * Copy of "System RAM (virtio_mem)" to be used for
> +        * add_memory_driver_managed().
> +        */
> +       const char *resource_name;
>
>         /* Summary of all memory block states. */
>         unsigned long nb_mb_state[VIRTIO_MEM_MB_STATE_COUNT];
> @@ -414,8 +419,20 @@ static int virtio_mem_mb_add(struct virtio_mem *vm, unsigned long mb_id)
>         if (nid == NUMA_NO_NODE)
>                 nid = memory_add_physaddr_to_nid(addr);
>
> +       /*
> +        * When force-unloading the driver and we still have memory added to
> +        * Linux, the resource name has to stay.
> +        */
> +       if (!vm->resource_name) {
> +               vm->resource_name = kstrdup_const("System RAM (virtio_mem)",
> +                                                 GFP_KERNEL);
> +               if (!vm->resource_name)
> +                       return -ENOMEM;
> +       }
> +
>         dev_dbg(&vm->vdev->dev, "adding memory block: %lu\n", mb_id);
> -       return add_memory(nid, addr, memory_block_size_bytes());
> +       return add_memory_driver_managed(nid, addr, memory_block_size_bytes(),
> +                                        vm->resource_name);
>  }
>
>  /*
> @@ -1890,10 +1907,12 @@ static void virtio_mem_remove(struct virtio_device *vdev)
>             vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL] ||
>             vm->nb_mb_state[VIRTIO_MEM_MB_STATE_ONLINE] ||
>             vm->nb_mb_state[VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL] ||
> -           vm->nb_mb_state[VIRTIO_MEM_MB_STATE_ONLINE_MOVABLE])
> +           vm->nb_mb_state[VIRTIO_MEM_MB_STATE_ONLINE_MOVABLE]) {
>                 dev_warn(&vdev->dev, "device still has system memory added\n");
> -       else
> +       } else {
>                 virtio_mem_delete_resource(vm);
> +               kfree_const(vm->resource_name);
> +       }
>
>         /* remove all tracking data - no locking needed */
>         vfree(vm->mb_state);

Looks good to me.
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>