Re: [PATCH] vhost-vdpa: fix potential memory leak during the release

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Nov 09, 2022 at 04:42:13PM +0100, Stefano Garzarella wrote:
> Before commit 3d5698793897 ("vhost-vdpa: introduce asid based IOTLB")
> we call vhost_vdpa_iotlb_unmap(v, iotlb, 0ULL, 0ULL - 1) during the
> release to free all the resources allocated when processing user IOTLB
> messages through vhost_vdpa_process_iotlb_update().
> That commit changed the handling of IOTLB a bit, and we accidentally
> removed some code called during the release.
> 
> We partially fixed with commit 037d4305569a ("vhost-vdpa: call
> vhost_vdpa_cleanup during the release") but a potential memory leak is
> still there as showed by kmemleak if the application does not send
> VHOST_IOTLB_INVALIDATE or crashes:
> 
>   unreferenced object 0xffff888007fbaa30 (size 16):
>     comm "blkio-bench", pid 914, jiffies 4294993521 (age 885.500s)
>     hex dump (first 16 bytes):
>       40 73 41 07 80 88 ff ff 00 00 00 00 00 00 00 00  @sA.............
>     backtrace:
>       [<0000000087736d2a>] kmem_cache_alloc_trace+0x142/0x1c0
>       [<0000000060740f50>] vhost_vdpa_process_iotlb_msg+0x68c/0x901 [vhost_vdpa]
>       [<0000000083e8e205>] vhost_chr_write_iter+0xc0/0x4a0 [vhost]
>       [<000000008f2f414a>] vhost_vdpa_chr_write_iter+0x18/0x20 [vhost_vdpa]
>       [<00000000de1cd4a0>] vfs_write+0x216/0x4b0
>       [<00000000a2850200>] ksys_write+0x71/0xf0
>       [<00000000de8e720b>] __x64_sys_write+0x19/0x20
>       [<0000000018b12cbb>] do_syscall_64+0x3f/0x90
>       [<00000000986ec465>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Let's fix calling vhost_vdpa_iotlb_unmap() on the whole range in
> vhost_vdpa_remove_as(). We move that call before vhost_dev_cleanup()
> since we need a valid v->vdev.mm in vhost_vdpa_pa_unmap().
> vhost_iotlb_reset() call can be removed, since vhost_vdpa_iotlb_unmap()
> on the whole range removes all the entries.
> 
> The kmemleak log reported was observed with a vDPA device that has `use_va`
> set to true (e.g. VDUSE). This patch has been tested with both types of
> devices.
> 
> Fixes: 037d4305569a ("vhost-vdpa: call vhost_vdpa_cleanup during the release")
> Fixes: 3d5698793897 ("vhost-vdpa: introduce asid based IOTLB")
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

It's fine, just pls don't say "potential" here in the subject, let's
avoid pleonasms - it's a memory leak, yes it triggers under some coditions
but little is unconditional in this world :)

No need to repost.

> ---
>  drivers/vhost/vdpa.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 166044642fd5..b08e07fc7d1f 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -65,6 +65,10 @@ static DEFINE_IDA(vhost_vdpa_ida);
>  
>  static dev_t vhost_vdpa_major;
>  
> +static void vhost_vdpa_iotlb_unmap(struct vhost_vdpa *v,
> +				   struct vhost_iotlb *iotlb,
> +				   u64 start, u64 last);
> +
>  static inline u32 iotlb_to_asid(struct vhost_iotlb *iotlb)
>  {
>  	struct vhost_vdpa_as *as = container_of(iotlb, struct
> @@ -135,7 +139,7 @@ static int vhost_vdpa_remove_as(struct vhost_vdpa *v, u32 asid)
>  		return -EINVAL;
>  
>  	hlist_del(&as->hash_link);
> -	vhost_iotlb_reset(&as->iotlb);
> +	vhost_vdpa_iotlb_unmap(v, &as->iotlb, 0ULL, 0ULL - 1);
>  	kfree(as);
>  
>  	return 0;
> @@ -1162,14 +1166,14 @@ static void vhost_vdpa_cleanup(struct vhost_vdpa *v)
>  	struct vhost_vdpa_as *as;
>  	u32 asid;
>  
> -	vhost_dev_cleanup(&v->vdev);
> -	kfree(v->vdev.vqs);
> -
>  	for (asid = 0; asid < v->vdpa->nas; asid++) {
>  		as = asid_to_as(v, asid);
>  		if (as)
>  			vhost_vdpa_remove_as(v, asid);
>  	}
> +
> +	vhost_dev_cleanup(&v->vdev);
> +	kfree(v->vdev.vqs);
>  }
>  
>  static int vhost_vdpa_open(struct inode *inode, struct file *filep)
> -- 
> 2.38.1

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