[2/2] xen/privcmd: Convert get_user_pages*() to pin_user_pages*()
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Message ID 1593054160-12628-2-git-send-email-jrdr.linux@gmail.com
State New
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Series
  • [1/2] xen/privcmd: Corrected error handling path and mark pages dirty
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Commit Message

Souptick Joarder June 25, 2020, 3:02 a.m. UTC
In 2019, we introduced pin_user_pages*() and now we are converting
get_user_pages*() to the new API as appropriate. [1] & [2] could
be referred for more information. This is case 5 as per document [1].

[1] Documentation/core-api/pin_user_pages.rst

[2] "Explicit pinning of user-space pages":
        https://lwn.net/Articles/807108/

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Paul Durrant <xadimgnik@gmail.com>
---
Hi,

I'm compile tested this, but unable to run-time test, so any testing
help is much appriciated.

 drivers/xen/privcmd.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

Comments

John Hubbard June 25, 2020, 5:49 a.m. UTC | #1
On 2020-06-24 20:02, Souptick Joarder wrote:
> In 2019, we introduced pin_user_pages*() and now we are converting
> get_user_pages*() to the new API as appropriate. [1] & [2] could
> be referred for more information. This is case 5 as per document [1].
> 
> [1] Documentation/core-api/pin_user_pages.rst
> 
> [2] "Explicit pinning of user-space pages":
>          https://lwn.net/Articles/807108/
> 
> Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Paul Durrant <xadimgnik@gmail.com>
> ---
> Hi,
> 
> I'm compile tested this, but unable to run-time test, so any testing
> help is much appriciated.
> 
>   drivers/xen/privcmd.c | 10 ++--------
>   1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 0da417c..eb05254 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -595,7 +595,7 @@ static int lock_pages(
>   		if (requested > nr_pages)
>   			return -ENOSPC;
>   
> -		page_count = get_user_pages_fast(
> +		page_count = pin_user_pages_fast(
>   			(unsigned long) kbufs[i].uptr,
>   			requested, FOLL_WRITE, pages);
>   		if (page_count < 0) {
> @@ -612,13 +612,7 @@ static int lock_pages(
>   
>   static void unlock_pages(struct page *pages[], unsigned int nr_pages)
>   {
> -	unsigned int i;
> -
> -	for (i = 0; i < nr_pages; i++) {
> -		if (!PageDirty(page))
> -			set_page_dirty_lock(page);
> -		put_page(pages[i]);
> -	}
> +	unpin_user_pages_dirty_lock(pages, nr_pages, 1);

"true", not "1", is the correct way to call that function.

Also, this approach changes the behavior slightly, but I think it's
reasonable to just set_page_dirty_lock() on the whole range--hard to
see much benefit in checking PageDirty first.


>   }
>   
>   static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
> 

thanks,
Souptick Joarder June 26, 2020, 5:26 a.m. UTC | #2
On Thu, Jun 25, 2020 at 11:19 AM John Hubbard <jhubbard@nvidia.com> wrote:
>
> On 2020-06-24 20:02, Souptick Joarder wrote:
> > In 2019, we introduced pin_user_pages*() and now we are converting
> > get_user_pages*() to the new API as appropriate. [1] & [2] could
> > be referred for more information. This is case 5 as per document [1].
> >
> > [1] Documentation/core-api/pin_user_pages.rst
> >
> > [2] "Explicit pinning of user-space pages":
> >          https://lwn.net/Articles/807108/
> >
> > Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
> > Cc: John Hubbard <jhubbard@nvidia.com>
> > Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> > Cc: Paul Durrant <xadimgnik@gmail.com>
> > ---
> > Hi,
> >
> > I'm compile tested this, but unable to run-time test, so any testing
> > help is much appriciated.
> >
> >   drivers/xen/privcmd.c | 10 ++--------
> >   1 file changed, 2 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> > index 0da417c..eb05254 100644
> > --- a/drivers/xen/privcmd.c
> > +++ b/drivers/xen/privcmd.c
> > @@ -595,7 +595,7 @@ static int lock_pages(
> >               if (requested > nr_pages)
> >                       return -ENOSPC;
> >
> > -             page_count = get_user_pages_fast(
> > +             page_count = pin_user_pages_fast(
> >                       (unsigned long) kbufs[i].uptr,
> >                       requested, FOLL_WRITE, pages);
> >               if (page_count < 0) {
> > @@ -612,13 +612,7 @@ static int lock_pages(
> >
> >   static void unlock_pages(struct page *pages[], unsigned int nr_pages)
> >   {
> > -     unsigned int i;
> > -
> > -     for (i = 0; i < nr_pages; i++) {
> > -             if (!PageDirty(page))
> > -                     set_page_dirty_lock(page);
> > -             put_page(pages[i]);
> > -     }
> > +     unpin_user_pages_dirty_lock(pages, nr_pages, 1);
>
> "true", not "1", is the correct way to call that function.

Ok.

>
> Also, this approach changes the behavior slightly, but I think it's
> reasonable to just set_page_dirty_lock() on the whole range--hard to
> see much benefit in checking PageDirty first.

unpin_user_pages_dirty_lock() internally will do the same check after
patch [2/2]
So I thought to keep old and new code in sync. Shall we avoid this check ?


>
>
> >   }
> >
> >   static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
> >
>
> thanks,
> --
> John Hubbard
> NVIDIA
John Hubbard June 26, 2020, 6:54 a.m. UTC | #3
On 2020-06-25 22:26, Souptick Joarder wrote:
> On Thu, Jun 25, 2020 at 11:19 AM John Hubbard <jhubbard@nvidia.com> wrote:
>> On 2020-06-24 20:02, Souptick Joarder wrote:
...
>>> @@ -612,13 +612,7 @@ static int lock_pages(
>>>
>>>    static void unlock_pages(struct page *pages[], unsigned int nr_pages)
>>>    {
>>> -     unsigned int i;
>>> -
>>> -     for (i = 0; i < nr_pages; i++) {
>>> -             if (!PageDirty(page))
>>> -                     set_page_dirty_lock(page);
>>> -             put_page(pages[i]);
>>> -     }
>>> +     unpin_user_pages_dirty_lock(pages, nr_pages, 1);
>>
>> "true", not "1", is the correct way to call that function.
> 
> Ok.
> 
>>
>> Also, this approach changes the behavior slightly, but I think it's

Correction, I forgot that I put that same if(!PageDirty(page)) check into
unpin_user_pages_dirty_lock(). So it doesn't change behavior. That's good.

>> reasonable to just set_page_dirty_lock() on the whole range--hard to
>> see much benefit in checking PageDirty first.
> 
> unpin_user_pages_dirty_lock() internally will do the same check after
> patch [2/2]
> So I thought to keep old and new code in sync. Shall we avoid this check ?
> 
Just leave it as you have it, but of course use "true" instead of 1, please.


thanks,

Patch
diff mbox series

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 0da417c..eb05254 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -595,7 +595,7 @@  static int lock_pages(
 		if (requested > nr_pages)
 			return -ENOSPC;
 
-		page_count = get_user_pages_fast(
+		page_count = pin_user_pages_fast(
 			(unsigned long) kbufs[i].uptr,
 			requested, FOLL_WRITE, pages);
 		if (page_count < 0) {
@@ -612,13 +612,7 @@  static int lock_pages(
 
 static void unlock_pages(struct page *pages[], unsigned int nr_pages)
 {
-	unsigned int i;
-
-	for (i = 0; i < nr_pages; i++) {
-		if (!PageDirty(page))
-			set_page_dirty_lock(page);
-		put_page(pages[i]);
-	}
+	unpin_user_pages_dirty_lock(pages, nr_pages, 1);
 }
 
 static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)