From: John Hubbard <jhubbard@nvidia.com>
To: Leon Romanovsky <leon@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Jason Gunthorpe <jgg@ziepe.ca>,
Christoph Hellwig <hch@infradead.org>,
Ira Weiny <ira.weiny@intel.com>, <linux-rdma@vger.kernel.org>,
<linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v2 1/2] mm/gup: allow FOLL_FORCE for get_user_pages_fast()
Date: Mon, 9 Dec 2019 11:54:36 -0800 [thread overview]
Message-ID: <7ceb9a54-6e2f-6d1f-70ba-f6ad5ba0b37f@nvidia.com> (raw)
In-Reply-To: <20191209182536.GC67461@unreal>
On 12/9/19 10:25 AM, Leon Romanovsky wrote:
> On Wed, Dec 04, 2019 at 01:36:02PM -0800, John Hubbard wrote:
>> 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().
>>
>> Fixes: 817be129e6f2 ("mm: validate get_user_pages_fast flags")
>> Cc: Christoph Hellwig <hch@lst.de>
>> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>> ---
>> mm/gup.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>
> Thanks,
> Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
>
Hi Leon, thanks for the reviews, great timing! I'll add the tags to
the commits, which I'm just about to post as part of the larger
"pin user pages" patchset.
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2019-12-09 19:54 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-04 21:36 [PATCH v2 0/2] IB/umem: use get_user_pages_fast() to pin DMA pages John Hubbard
2019-12-04 21:36 ` [PATCH v2 1/2] mm/gup: allow FOLL_FORCE for get_user_pages_fast() John Hubbard
2019-12-09 18:25 ` Leon Romanovsky
2019-12-09 19:54 ` John Hubbard [this message]
2019-12-04 21:36 ` [PATCH v2 2/2] IB/umem: use get_user_pages_fast() to pin DMA pages John Hubbard
2019-12-09 18:25 ` Leon Romanovsky
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