Re: [PATCH v13 16/20] IB/mlx4, arm64: untag user pointers in mlx4_get_umem_mr

[Leon Romanovsky <leon@kernel.org>]

On Wed, Mar 20, 2019 at 03:51:30PM +0100, Andrey Konovalov wrote:
> This patch is a part of a series that extends arm64 kernel ABI to allow to
> pass tagged user pointers (with the top byte set to something else other
> than 0x00) as syscall arguments.
>
> mlx4_get_umem_mr() uses provided user pointers for vma lookups, which can
> only by done with untagged pointers.
>
> Untag user pointers in this function.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
>  drivers/infiniband/hw/mlx4/mr.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/infiniband/hw/mlx4/mr.c b/drivers/infiniband/hw/mlx4/mr.c
> index 395379a480cb..9a35ed2c6a6f 100644
> --- a/drivers/infiniband/hw/mlx4/mr.c
> +++ b/drivers/infiniband/hw/mlx4/mr.c
> @@ -378,6 +378,7 @@ static struct ib_umem *mlx4_get_umem_mr(struct ib_udata *udata, u64 start,
>  	 * again
>  	 */
>  	if (!ib_access_writable(access_flags)) {
> +		unsigned long untagged_start = untagged_addr(start);
>  		struct vm_area_struct *vma;
>
>  		down_read(&current->mm->mmap_sem);
> @@ -386,9 +387,9 @@ static struct ib_umem *mlx4_get_umem_mr(struct ib_udata *udata, u64 start,
>  		 * cover the memory, but for now it requires a single vma to
>  		 * entirely cover the MR to support RO mappings.
>  		 */
> -		vma = find_vma(current->mm, start);
> -		if (vma && vma->vm_end >= start + length &&
> -		    vma->vm_start <= start) {
> +		vma = find_vma(current->mm, untagged_start);
> +		if (vma && vma->vm_end >= untagged_start + length &&
> +		    vma->vm_start <= untagged_start) {
>  			if (vma->vm_flags & VM_WRITE)
>  				access_flags |= IB_ACCESS_LOCAL_WRITE;
>  		} else {
> --

Thanks,
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>

Interesting, the followup question is why mlx4 is only one driver in IB which
needs such code in umem_mr. I'll take a look on it.

Thanks