RE: [PATCH] vdpa_sim: avoid putting an uninitialized iova_domain

[Parav Pandit <parav@nvidia.com>]

> From: Longpeng(Mike) <longpeng2@huawei.com>
> Sent: Monday, November 22, 2021 5:52 PM
> 
> From: Longpeng <longpeng2@huawei.com>
> 
> The system will crash if we put an uninitialized iova_domain, this could
> happen when an error occurs before initializing the iova_domain in
> vdpasim_create().
> 
> BUG: kernel NULL pointer dereference, address: 0000000000000000 ...
> RIP: 0010:__cpuhp_state_remove_instance+0x96/0x1c0
> ...
> Call Trace:
>  <TASK>
>  put_iova_domain+0x29/0x220
>  vdpasim_free+0xd1/0x120 [vdpa_sim]
>  vdpa_release_dev+0x21/0x40 [vdpa]
>  device_release+0x33/0x90
>  kobject_release+0x63/0x160
>  vdpasim_create+0x127/0x2a0 [vdpa_sim]
>  vdpasim_net_dev_add+0x7d/0xfe [vdpa_sim_net]
>  vdpa_nl_cmd_dev_add_set_doit+0xe1/0x1a0 [vdpa]
>  genl_family_rcv_msg_doit+0x112/0x140
>  genl_rcv_msg+0xdf/0x1d0
>  ...
> 
> So we must make sure the iova_domain is already initialized before put it.
> 
> In addition, we may get the following warning in this case:
> WARNING: ... drivers/iommu/iova.c:344 iova_cache_put+0x58/0x70
> 
> So we must make sure the iova_cache_put() is invoked only if the
> iova_cache_get() is already invoked. Let's fix it together.
> 
> Signed-off-by: Longpeng <longpeng2@huawei.com>

Can you please add the fixes tag here so that older kernels can take this fix?