From mboxrd@z Thu Jan  1 00:00:00 1970
From: Khalid Aziz <khalid.aziz@oracle.com>
Subject: Re: [PATCH v16 04/16] mm: untag user pointers in do_pages_move
Date: Tue, 11 Jun 2019 14:18:18 -0600
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To: Andrey Konovalov <andreyknvl@google.com>, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-rdma@vger.kernel.org, linux-media@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org
Cc: Mark Rutland <mark.rutland@arm.com>, Szabolcs Nagy <Szabolcs.Nagy@arm.com>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Kostya Serebryany <kcc@google.com>, Felix Kuehling <Felix.Kuehling@amd.com>, Vincenzo Frascino <vincenzo.frascino@arm.com>, Jacob Bramley <Jacob.Bramley@arm.com>, Leon Romanovsky <leon@kernel.org>, Christoph Hellwig <hch@infradead.org>, Jason Gunthorpe <jgg@ziepe.ca>, Dave Martin <Dave.Martin@arm.com>, Evgeniy Stepanov <eugenis@google.com>, Kevin Brodsky <kevin.brodsky@arm.com>, Kees Cook <keescook@chromium.org>, Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>, Alex Williamson <alex.williamson@redhat.com>, Mauro Carvalho Chehab <mchehab@kernel.org>, Dmitry Vyukov <dvyukov@google.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Yishai Hadas <yishaih@mellanox.com>J
List-Id: linux-rdma@vger.kernel.org

On 6/3/19 10:55 AM, 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.
> 
> do_pages_move() is used in the implementation of the move_pages syscall.
> 
> Untag user pointers in this function.
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
>  mm/migrate.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index f2ecc2855a12..3930bb6fa656 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1617,6 +1617,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
>  		if (get_user(node, nodes + i))
>  			goto out_flush;
>  		addr = (unsigned long)p;
> +		addr = untagged_addr(addr);

Why not just "addr = (unsigned long)untagged_addr(p);"

--
Khalid