From: John Hubbard <jhubbard@nvidia.com>
To: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH 1/2] mm/gup: introduce pin_user_pages_locked()
Date: Sun, 31 May 2020 12:52:21 -0700 [thread overview]
Message-ID: <d11d52f8-d54c-bb45-bde9-198235a03921@nvidia.com> (raw)
In-Reply-To: <CAFqt6zZr9rUZaXEpjwmtmicdNP9KhJ8UrjPPjk4bMHJ20VsVsg@mail.gmail.com>
On 2020-05-31 00:04, Souptick Joarder wrote:
...
>> +/*
>> + * pin_user_pages_locked() is the FOLL_PIN variant of get_user_pages_locked().
>> + * Behavior is the same, except that this one sets FOLL_PIN and rejects
>> + * FOLL_GET.
>> + */
>> +long pin_user_pages_locked(unsigned long start, unsigned long nr_pages,
>> + unsigned int gup_flags, struct page **pages,
>> + int *locked)
>> +{
>> + /*
>> + * FIXME: Current FOLL_LONGTERM behavior is incompatible with
>> + * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
>> + * vmas. As there are no users of this flag in this call we simply
>> + * disallow this option for now.
>> + */
>> + if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
>> + return -EINVAL;
>> +
>> + /* FOLL_GET and FOLL_PIN are mutually exclusive. */
>> + if (WARN_ON_ONCE(gup_flags & FOLL_GET))
>> + return -EINVAL;
>> +
>> + gup_flags |= FOLL_PIN;
>
> Right now get_user_pages_locked() doesn't have similar check for FOLL_PIN
Yes, that should be added...
> and also not setting FOLL_GET internally irrespective of gup_flags
> passed by user.
> Do we need to add the same in get_user_pages_locked() ?
...and no, that should not.
Yes, it's prudent to assert that FOLL_PIN is *not* set, at all the
get_user_pages*() API calls, thanks for spotting that. I'll add that to
this patch and send out a v2.
The same check should also be added to get_user_pages_unlocked(). I'll send
out a correction (I think just a v3 of that patchset) to add that.
The setting of FOLL_GET, on the other hand, is something best left as-is
so far. Some call sites set FOLL_GET, some want it *not* set, and some
expect that FOLL_GET is implied, and at the moment, the delicate balance is
correct. :)
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2020-05-31 19:52 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-27 22:32 [PATCH 0/2] mm/gup: introduce pin_user_pages_locked(), use it in frame_vector.c John Hubbard
2020-05-27 22:32 ` [PATCH 1/2] mm/gup: introduce pin_user_pages_locked() John Hubbard
2020-05-28 8:43 ` David Hildenbrand
2020-05-31 7:04 ` Souptick Joarder
2020-05-31 7:13 ` Souptick Joarder
2020-05-31 19:56 ` John Hubbard
2020-05-31 19:52 ` John Hubbard [this message]
2020-05-31 13:03 ` Pankaj Gupta
2020-05-27 22:32 ` [PATCH 2/2] mm/gup: frame_vector: convert get_user_pages() --> pin_user_pages() John Hubbard
2020-05-28 8:46 ` David Hildenbrand
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