diff mbox series

[1/2] mm/gup: introduce pin_user_pages_locked()

Message ID 20200527223243.884385-2-jhubbard@nvidia.com (mailing list archive)
State New, archived
Headers show
Series mm/gup: introduce pin_user_pages_locked(), use it in frame_vector.c | expand

Commit Message

John Hubbard May 27, 2020, 10:32 p.m. UTC
Introduce pin_user_pages_locked(), which is nearly identical to
get_user_pages_locked() except that it sets FOLL_PIN and rejects
FOLL_GET.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/mm.h |  2 ++
 mm/gup.c           | 30 ++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

Comments

David Hildenbrand May 28, 2020, 8:43 a.m. UTC | #1
On 28.05.20 00:32, John Hubbard wrote:
> Introduce pin_user_pages_locked(), which is nearly identical to
> get_user_pages_locked() except that it sets FOLL_PIN and rejects
> FOLL_GET.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  include/linux/mm.h |  2 ++
>  mm/gup.c           | 30 ++++++++++++++++++++++++++++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 98be7289d7e9..d16951087c93 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1700,6 +1700,8 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages,
>  		    struct vm_area_struct **vmas);
>  long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
>  		    unsigned int gup_flags, struct page **pages, int *locked);
> +long pin_user_pages_locked(unsigned long start, unsigned long nr_pages,
> +		    unsigned int gup_flags, struct page **pages, int *locked);
>  long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
>  		    struct page **pages, unsigned int gup_flags);
>  long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> diff --git a/mm/gup.c b/mm/gup.c
> index 2f0a0b497c23..17418a949067 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2992,3 +2992,33 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
>  	return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
>  }
>  EXPORT_SYMBOL(pin_user_pages_unlocked);
> +
> +/*
> + * 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;
> +	return __get_user_pages_locked(current, current->mm, start, nr_pages,
> +				       pages, NULL, locked,
> +				       gup_flags | FOLL_TOUCH);
> +}
> +EXPORT_SYMBOL(pin_user_pages_locked);
> +
> 

LGTM

Reviewed-by: David Hildenbrand <david@redhat.com>
Souptick Joarder May 31, 2020, 7:04 a.m. UTC | #2
On Thu, May 28, 2020 at 4:02 AM John Hubbard <jhubbard@nvidia.com> wrote:
>
> Introduce pin_user_pages_locked(), which is nearly identical to
> get_user_pages_locked() except that it sets FOLL_PIN and rejects
> FOLL_GET.
>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  include/linux/mm.h |  2 ++
>  mm/gup.c           | 30 ++++++++++++++++++++++++++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 98be7289d7e9..d16951087c93 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1700,6 +1700,8 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages,
>                     struct vm_area_struct **vmas);
>  long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
>                     unsigned int gup_flags, struct page **pages, int *locked);
> +long pin_user_pages_locked(unsigned long start, unsigned long nr_pages,
> +                   unsigned int gup_flags, struct page **pages, int *locked);
>  long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
>                     struct page **pages, unsigned int gup_flags);
>  long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> diff --git a/mm/gup.c b/mm/gup.c
> index 2f0a0b497c23..17418a949067 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2992,3 +2992,33 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
>         return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
>  }
>  EXPORT_SYMBOL(pin_user_pages_unlocked);
> +
> +/*
> + * 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
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() ?

> +       return __get_user_pages_locked(current, current->mm, start, nr_pages,
> +                                      pages, NULL, locked,
> +                                      gup_flags | FOLL_TOUCH);
> +}
> +EXPORT_SYMBOL(pin_user_pages_locked);
> +
> --
> 2.26.2
>
>
Souptick Joarder May 31, 2020, 7:13 a.m. UTC | #3
On Sun, May 31, 2020 at 12:34 PM Souptick Joarder <jrdr.linux@gmail.com> wrote:
>
> On Thu, May 28, 2020 at 4:02 AM John Hubbard <jhubbard@nvidia.com> wrote:
> >
> > Introduce pin_user_pages_locked(), which is nearly identical to
> > get_user_pages_locked() except that it sets FOLL_PIN and rejects
> > FOLL_GET.

Forget to ask, is it fine to add this new pin_user_pages_locked() in
Documentation/core-api/pin_user_pages.rst ?

> >
> > Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> > ---
> >  include/linux/mm.h |  2 ++
> >  mm/gup.c           | 30 ++++++++++++++++++++++++++++++
> >  2 files changed, 32 insertions(+)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 98be7289d7e9..d16951087c93 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -1700,6 +1700,8 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages,
> >                     struct vm_area_struct **vmas);
> >  long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
> >                     unsigned int gup_flags, struct page **pages, int *locked);
> > +long pin_user_pages_locked(unsigned long start, unsigned long nr_pages,
> > +                   unsigned int gup_flags, struct page **pages, int *locked);
> >  long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> >                     struct page **pages, unsigned int gup_flags);
> >  long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 2f0a0b497c23..17418a949067 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -2992,3 +2992,33 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> >         return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
> >  }
> >  EXPORT_SYMBOL(pin_user_pages_unlocked);
> > +
> > +/*
> > + * 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
> 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() ?
>
> > +       return __get_user_pages_locked(current, current->mm, start, nr_pages,
> > +                                      pages, NULL, locked,
> > +                                      gup_flags | FOLL_TOUCH);
> > +}
> > +EXPORT_SYMBOL(pin_user_pages_locked);
> > +
> > --
> > 2.26.2
> >
> >
Pankaj Gupta May 31, 2020, 1:03 p.m. UTC | #4
Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>

On Thu, 28 May 2020 at 00:32, John Hubbard <jhubbard@nvidia.com> wrote:
>
> Introduce pin_user_pages_locked(), which is nearly identical to
> get_user_pages_locked() except that it sets FOLL_PIN and rejects
> FOLL_GET.
>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  include/linux/mm.h |  2 ++
>  mm/gup.c           | 30 ++++++++++++++++++++++++++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 98be7289d7e9..d16951087c93 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1700,6 +1700,8 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages,
>                     struct vm_area_struct **vmas);
>  long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
>                     unsigned int gup_flags, struct page **pages, int *locked);
> +long pin_user_pages_locked(unsigned long start, unsigned long nr_pages,
> +                   unsigned int gup_flags, struct page **pages, int *locked);
>  long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
>                     struct page **pages, unsigned int gup_flags);
>  long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> diff --git a/mm/gup.c b/mm/gup.c
> index 2f0a0b497c23..17418a949067 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2992,3 +2992,33 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
>         return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
>  }
>  EXPORT_SYMBOL(pin_user_pages_unlocked);
> +
> +/*
> + * 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;
> +       return __get_user_pages_locked(current, current->mm, start, nr_pages,
> +                                      pages, NULL, locked,
> +                                      gup_flags | FOLL_TOUCH);
> +}
> +EXPORT_SYMBOL(pin_user_pages_locked);
> +
> --
> 2.26.2
>
>
John Hubbard May 31, 2020, 7:52 p.m. UTC | #5
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 May 31, 2020, 7:56 p.m. UTC | #6
On 2020-05-31 00:13, Souptick Joarder wrote:
> On Sun, May 31, 2020 at 12:34 PM Souptick Joarder <jrdr.linux@gmail.com> wrote:
>>
>> On Thu, May 28, 2020 at 4:02 AM John Hubbard <jhubbard@nvidia.com> wrote:
>>>
>>> Introduce pin_user_pages_locked(), which is nearly identical to
>>> get_user_pages_locked() except that it sets FOLL_PIN and rejects
>>> FOLL_GET.
> 
> Forget to ask, is it fine to add this new pin_user_pages_locked() in
> Documentation/core-api/pin_user_pages.rst ?
> 
I wasn't planning on maintaining a rigorous list of all of the pin_user_page*()
API calls, in pin_user_pages.rst. Each call is documented in gup.c, for  that.
The .rst is there to help explain things at a slighly higher abstraction level.

thanks,
diff mbox series

Patch

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 98be7289d7e9..d16951087c93 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1700,6 +1700,8 @@  long pin_user_pages(unsigned long start, unsigned long nr_pages,
 		    struct vm_area_struct **vmas);
 long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
 		    unsigned int gup_flags, struct page **pages, int *locked);
+long pin_user_pages_locked(unsigned long start, unsigned long nr_pages,
+		    unsigned int gup_flags, struct page **pages, int *locked);
 long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 		    struct page **pages, unsigned int gup_flags);
 long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
diff --git a/mm/gup.c b/mm/gup.c
index 2f0a0b497c23..17418a949067 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2992,3 +2992,33 @@  long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 	return get_user_pages_unlocked(start, nr_pages, pages, gup_flags);
 }
 EXPORT_SYMBOL(pin_user_pages_unlocked);
+
+/*
+ * 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;
+	return __get_user_pages_locked(current, current->mm, start, nr_pages,
+				       pages, NULL, locked,
+				       gup_flags | FOLL_TOUCH);
+}
+EXPORT_SYMBOL(pin_user_pages_locked);
+