Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, John Hubbard <jhubbard@nvidia.com>,
        Leon Romanovsky <leonro@mellanox.com>, Jan Kara <jack@suse.cz>,
        Christoph Hellwig <hch@lst.de>,
        Alex Williamson <alex.williamson@redhat.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= <bjorn.topel@intel.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Dan Williams <dan.j.williams@intel.com>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Ira Weiny <ira.weiny@intel.com>,
        Jason Gunthorpe <jgg@mellanox.com>,
        Jason Gunthorpe <jgg@ziepe.ca>, Jens Axboe <axboe@kernel.dk>,
        Jerome Glisse <jglisse@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 5.4 148/152] mm/gup: allow FOLL_FORCE for get_user_pages_fast()
Date:   Tue,  3 Mar 2020 18:44:06 +0100
Message-Id: <20200303174319.624614911@linuxfoundation.org>
In-Reply-To: <20200303174302.523080016@linuxfoundation.org>
References: <20200303174302.523080016@linuxfoundation.org>
User-Agent: quilt/0.66
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: John Hubbard <jhubbard@nvidia.com>

commit f4000fdf435b8301a11cf85237c561047f8c4c72 upstream.

Commit 817be129e6f2 ("mm: validate get_user_pages_fast flags") allowed
only FOLL_WRITE and FOLL_LONGTERM to be passed to get_user_pages_fast().
This, combined with the fact that get_user_pages_fast() falls back to
"slow gup", which *does* accept FOLL_FORCE, leads to an odd situation:
if you need FOLL_FORCE, you cannot call get_user_pages_fast().

There does not appear to be any reason for filtering out FOLL_FORCE.
There is nothing in the _fast() implementation that requires that we
avoid writing to the pages.  So it appears to have been an oversight.

Fix by allowing FOLL_FORCE to be set for get_user_pages_fast().

Link: http://lkml.kernel.org/r/20200107224558.2362728-9-jhubbard@nvidia.com
Fixes: 817be129e6f2 ("mm: validate get_user_pages_fast flags")
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Björn Töpel <bjorn.topel@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/gup.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2401,7 +2401,8 @@ int get_user_pages_fast(unsigned long st
 	unsigned long addr, len, end;
 	int nr = 0, ret = 0;
 
-	if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM)))
+	if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
+				       FOLL_FORCE)))
 		return -EINVAL;
 
 	start = untagged_addr(start) & PAGE_MASK;