Re: [PATCH v14 13/17] IB/mlx4, arm64: untag user pointers in mlx4_get_umem_mr

From: Catalin Marinas <catalin.marinas@arm.com>
To: Andrey Konovalov <andreyknvl@google.com>
Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
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	Dave Martin <Dave.Martin@arm.com>,
	Kevin Brodsky <kevin.brodsky@arm.com>,
	Szabolcs Nagy <Szabolcs.Nagy@arm.com>,
	Leon Romanovsky <leonro@mellanox.com>
Subject: Re: [PATCH v14 13/17] IB/mlx4, arm64: untag user pointers in mlx4_get_umem_mr
Date: Fri, 3 May 2019 18:03:10 +0100	[thread overview]
Message-ID: <20190503170310.GL55449@arrakis.emea.arm.com> (raw)
In-Reply-To: <05c0c078b8b5984af4cc3b105a58c711dcd83342.1556630205.git.andreyknvl@google.com>

On Tue, Apr 30, 2019 at 03:25:09PM +0200, 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>
> Reviewed-by: Leon Romanovsky <leonro@mellanox.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 {

Discussion ongoing on the previous version of the patch but I'm more
inclined to do this in ib_uverbs_(re)reg_mr() on cmd.start.

-- 
Catalin