[PATCH 0/3] binder: Use kmap_local_page() in binder_alloc.c

[PATCH 0/3] binder: Use kmap_local_page() in binder_alloc.c

[Fabio M. De Francesco]

Use kmap_local_page() in binder_alloc.c because kmap() and kmap_atomic()
are being deprecated and kmap_local_page is preferred where it is feasible.

With kmap_local_page(), the mapping is per thread, CPU local and not
globally visible. Furthermore, the mapping can be acquired from any
context, including interrupts.

Fabio M. De Francesco (3):
  binder: Use memset_page() in binder_alloc_clear_buf()
  binder: Use kmap_local_page() in binder_alloc_copy_user_to_buffer()
  binder: Use kmap_local_page() in binder_alloc_get_page()

 drivers/android/binder_alloc.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

-- 
2.34.1

[PATCH 1/3] binder: Use memset_page() in binder_alloc_clear_buf()

[Fabio M. De Francesco]

The use of kmap() is being deprecated in favor of kmap_local_page()
where it is feasible. With kmap_local_page(), the mapping is per
thread, CPU local and not globally visible.

binder_alloc_clear_buf() is a function where the use of kmap_local_page()
in place of kmap() is correctly suited because the mapping is local to the
thread.

Therefore, use kmap_local_page() / kunmap_local() but, instead of open
coding these two functions and adding a memset() of the virtual address
of the mapping, prefer memset_page().

Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---
 drivers/android/binder_alloc.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 2ac1008a5f39..0b3f2f569053 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -1175,14 +1175,11 @@ static void binder_alloc_clear_buf(struct binder_alloc *alloc,
 		unsigned long size;
 		struct page *page;
 		pgoff_t pgoff;
-		void *kptr;
 
 		page = binder_alloc_get_page(alloc, buffer,
 					     buffer_offset, &pgoff);
 		size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
-		kptr = kmap(page) + pgoff;
-		memset(kptr, 0, size);
-		kunmap(page);
+		memset_page(page, pgoff, 0, size);
 		bytes -= size;
 		buffer_offset += size;
 	}
-- 
2.34.1

Re: [PATCH 1/3] binder: Use memset_page() in binder_alloc_clear_buf()

[Todd Kjos]

On Sat, Apr 23, 2022 at 3:24 AM Fabio M. De Francesco
<fmdefrancesco@gmail.com> wrote:
>
> The use of kmap() is being deprecated in favor of kmap_local_page()
> where it is feasible. With kmap_local_page(), the mapping is per
> thread, CPU local and not globally visible.
>
> binder_alloc_clear_buf() is a function where the use of kmap_local_page()
> in place of kmap() is correctly suited because the mapping is local to the
> thread.
>
> Therefore, use kmap_local_page() / kunmap_local() but, instead of open
> coding these two functions and adding a memset() of the virtual address
> of the mapping, prefer memset_page().
>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>

Acked-by: Todd Kjos <tkjos@google.com>

> ---
>  drivers/android/binder_alloc.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index 2ac1008a5f39..0b3f2f569053 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -1175,14 +1175,11 @@ static void binder_alloc_clear_buf(struct binder_alloc *alloc,
>                 unsigned long size;
>                 struct page *page;
>                 pgoff_t pgoff;
> -               void *kptr;
>
>                 page = binder_alloc_get_page(alloc, buffer,
>                                              buffer_offset, &pgoff);
>                 size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
> -               kptr = kmap(page) + pgoff;
> -               memset(kptr, 0, size);
> -               kunmap(page);
> +               memset_page(page, pgoff, 0, size);
>                 bytes -= size;
>                 buffer_offset += size;
>         }
> --
> 2.34.1
>

[PATCH 2/3] binder: Use kmap_local_page() in binder_alloc_copy_user_to_buffer()

[Fabio M. De Francesco]

The use of kmap() is being deprecated in favor of kmap_local_page()
where it is feasible. With kmap_local_page(), the mapping is per
thread, CPU local and not globally visible.

binder_alloc_copy_user_to_buffer() is a function where the use of
kmap_local_page() in place of kmap() is correctly suited because
the mapping is local to the thread.

Therefore, use kmap_local_page() / kunmap_local().

Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---
 drivers/android/binder_alloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 0b3f2f569053..0875c463c002 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -1217,9 +1217,9 @@ binder_alloc_copy_user_to_buffer(struct binder_alloc *alloc,
 		page = binder_alloc_get_page(alloc, buffer,
 					     buffer_offset, &pgoff);
 		size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
-		kptr = kmap(page) + pgoff;
+		kptr = kmap_local_page(page) + pgoff;
 		ret = copy_from_user(kptr, from, size);
-		kunmap(page);
+		kunmap_local(kptr);
 		if (ret)
 			return bytes - size + ret;
 		bytes -= size;
-- 
2.34.1

Re: [PATCH 2/3] binder: Use kmap_local_page() in binder_alloc_copy_user_to_buffer()

[Todd Kjos]

On Sat, Apr 23, 2022 at 3:24 AM Fabio M. De Francesco
<fmdefrancesco@gmail.com> wrote:
>
> The use of kmap() is being deprecated in favor of kmap_local_page()
> where it is feasible. With kmap_local_page(), the mapping is per
> thread, CPU local and not globally visible.
>
> binder_alloc_copy_user_to_buffer() is a function where the use of
> kmap_local_page() in place of kmap() is correctly suited because
> the mapping is local to the thread.
>
> Therefore, use kmap_local_page() / kunmap_local().
>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>

Acked-by: Todd Kjos <tkjos@google.com>

> ---
>  drivers/android/binder_alloc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index 0b3f2f569053..0875c463c002 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -1217,9 +1217,9 @@ binder_alloc_copy_user_to_buffer(struct binder_alloc *alloc,
>                 page = binder_alloc_get_page(alloc, buffer,
>                                              buffer_offset, &pgoff);
>                 size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
> -               kptr = kmap(page) + pgoff;
> +               kptr = kmap_local_page(page) + pgoff;
>                 ret = copy_from_user(kptr, from, size);
> -               kunmap(page);
> +               kunmap_local(kptr);
>                 if (ret)
>                         return bytes - size + ret;
>                 bytes -= size;
> --
> 2.34.1
>

[PATCH 3/3] binder: Use kmap_local_page() in binder_alloc_get_page()

[Fabio M. De Francesco]

The use of kmap_atomic() is being deprecated in favor of kmap_local_page()
where it is feasible. Each call of kmap_atomic() in the kernel creates
a non-preemptible section and disable pagefaults. This could be a source
of unwanted latency, so it should be only used if it is absolutely
required, otherwise kmap_local_page() should be preferred.

With kmap_local_page(), the mapping is per thread, CPU local and not
globally visible. Furthermore, the mapping can be acquired from any context
(including interrupts).

Therefore, use kmap_local_page() / kunmap_local() in place of
kmap_atomic() / kunmap_atomic().

Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---
 drivers/android/binder_alloc.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 0875c463c002..058595cc7ff0 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -1250,17 +1250,17 @@ static int binder_alloc_do_buffer_copy(struct binder_alloc *alloc,
 		page = binder_alloc_get_page(alloc, buffer,
 					     buffer_offset, &pgoff);
 		size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
-		base_ptr = kmap_atomic(page);
+		base_ptr = kmap_local_page(page);
 		tmpptr = base_ptr + pgoff;
 		if (to_buffer)
 			memcpy(tmpptr, ptr, size);
 		else
 			memcpy(ptr, tmpptr, size);
 		/*
-		 * kunmap_atomic() takes care of flushing the cache
+		 * kunmap_local() takes care of flushing the cache
 		 * if this device has VIVT cache arch
 		 */
-		kunmap_atomic(base_ptr);
+		kunmap_local(base_ptr);
 		bytes -= size;
 		pgoff = 0;
 		ptr = ptr + size;
-- 
2.34.1

Re: [PATCH 3/3] binder: Use kmap_local_page() in binder_alloc_get_page()

[Todd Kjos]

On Sat, Apr 23, 2022 at 3:24 AM Fabio M. De Francesco
<fmdefrancesco@gmail.com> wrote:
>
> The use of kmap_atomic() is being deprecated in favor of kmap_local_page()
> where it is feasible. Each call of kmap_atomic() in the kernel creates
> a non-preemptible section and disable pagefaults. This could be a source
> of unwanted latency, so it should be only used if it is absolutely
> required, otherwise kmap_local_page() should be preferred.
>
> With kmap_local_page(), the mapping is per thread, CPU local and not
> globally visible. Furthermore, the mapping can be acquired from any context
> (including interrupts).
>
> Therefore, use kmap_local_page() / kunmap_local() in place of
> kmap_atomic() / kunmap_atomic().
>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>

Acked-by: Todd Kjos <tkjos@google.com>

> ---
>  drivers/android/binder_alloc.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index 0875c463c002..058595cc7ff0 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -1250,17 +1250,17 @@ static int binder_alloc_do_buffer_copy(struct binder_alloc *alloc,
>                 page = binder_alloc_get_page(alloc, buffer,
>                                              buffer_offset, &pgoff);
>                 size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
> -               base_ptr = kmap_atomic(page);
> +               base_ptr = kmap_local_page(page);
>                 tmpptr = base_ptr + pgoff;
>                 if (to_buffer)
>                         memcpy(tmpptr, ptr, size);
>                 else
>                         memcpy(ptr, tmpptr, size);
>                 /*
> -                * kunmap_atomic() takes care of flushing the cache
> +                * kunmap_local() takes care of flushing the cache
>                  * if this device has VIVT cache arch
>                  */
> -               kunmap_atomic(base_ptr);
> +               kunmap_local(base_ptr);
>                 bytes -= size;
>                 pgoff = 0;
>                 ptr = ptr + size;
> --
> 2.34.1
>

Re: [PATCH 3/3] binder: Use kmap_local_page() in binder_alloc_get_page()

[Christophe JAILLET]

Hi,

Le 23/04/2022 à 12:24, Fabio M. De Francesco a écrit :
> The use of kmap_atomic() is being deprecated in favor of kmap_local_page()
> where it is feasible. Each call of kmap_atomic() in the kernel creates
> a non-preemptible section and disable pagefaults. This could be a source
> of unwanted latency, so it should be only used if it is absolutely
> required, otherwise kmap_local_page() should be preferred.
> 
> With kmap_local_page(), the mapping is per thread, CPU local and not
> globally visible. Furthermore, the mapping can be acquired from any context
> (including interrupts).
> 
> Therefore, use kmap_local_page() / kunmap_local() in place of
> kmap_atomic() / kunmap_atomic().
> 
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
>   drivers/android/binder_alloc.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index 0875c463c002..058595cc7ff0 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -1250,17 +1250,17 @@ static int binder_alloc_do_buffer_copy(struct binder_alloc *alloc,
>   		page = binder_alloc_get_page(alloc, buffer,
>   					     buffer_offset, &pgoff);
>   		size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
> -		base_ptr = kmap_atomic(page);
> +		base_ptr = kmap_local_page(page);
>   		tmpptr = base_ptr + pgoff;
>   		if (to_buffer)
>   			memcpy(tmpptr, ptr, size);
>   		else
>   			memcpy(ptr, tmpptr, size);

in the same spirit as patch 1/3, memcpy_to_page() and memcpy_from_page() 
looks good candidate to avoid code duplication.

Not checked in details, but looks mostly the same.

Just my 2c.

CJ

>   		/*
> -		 * kunmap_atomic() takes care of flushing the cache
> +		 * kunmap_local() takes care of flushing the cache
>   		 * if this device has VIVT cache arch
>   		 */
> -		kunmap_atomic(base_ptr);
> +		kunmap_local(base_ptr);
>   		bytes -= size;
>   		pgoff = 0;
>   		ptr = ptr + size;

Re: [PATCH 3/3] binder: Use kmap_local_page() in binder_alloc_get_page()

[Christophe JAILLET]

Hi,

Le 23/04/2022 à 12:24, Fabio M. De Francesco a écrit :
> The use of kmap_atomic() is being deprecated in favor of kmap_local_page()
> where it is feasible. Each call of kmap_atomic() in the kernel creates
> a non-preemptible section and disable pagefaults. This could be a source
> of unwanted latency, so it should be only used if it is absolutely
> required, otherwise kmap_local_page() should be preferred.
> 
> With kmap_local_page(), the mapping is per thread, CPU local and not
> globally visible. Furthermore, the mapping can be acquired from any context
> (including interrupts).
> 
> Therefore, use kmap_local_page() / kunmap_local() in place of
> kmap_atomic() / kunmap_atomic().
> 
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
>   drivers/android/binder_alloc.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index 0875c463c002..058595cc7ff0 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -1250,17 +1250,17 @@ static int binder_alloc_do_buffer_copy(struct binder_alloc *alloc,
>   		page = binder_alloc_get_page(alloc, buffer,
>   					     buffer_offset, &pgoff);
>   		size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
> -		base_ptr = kmap_atomic(page);
> +		base_ptr = kmap_local_page(page);
>   		tmpptr = base_ptr + pgoff;
>   		if (to_buffer)
>   			memcpy(tmpptr, ptr, size);
>   		else
>   			memcpy(ptr, tmpptr, size);

in the same spirit as patch 1/3, memcpy_to_page() and memcpy_from_page() 
looks good candidate to avoid code duplication.

Not checked in details, but looks mostly the same.

Just my 2c.

CJ

>   		/*
> -		 * kunmap_atomic() takes care of flushing the cache
> +		 * kunmap_local() takes care of flushing the cache
>   		 * if this device has VIVT cache arch
>   		 */
> -		kunmap_atomic(base_ptr);
> +		kunmap_local(base_ptr);
>   		bytes -= size;
>   		pgoff = 0;
>   		ptr = ptr + size;

Re: [PATCH 3/3] binder: Use kmap_local_page() in binder_alloc_get_page()

[Fabio M. De Francesco]

On sabato 23 aprile 2022 18:02:48 CEST Christophe JAILLET wrote:
> Hi,
> 
> Le 23/04/2022 à 12:24, Fabio M. De Francesco a écrit :
> > The use of kmap_atomic() is being deprecated in favor of 
kmap_local_page()
> > where it is feasible. Each call of kmap_atomic() in the kernel creates
> > a non-preemptible section and disable pagefaults. This could be a 
source
> > of unwanted latency, so it should be only used if it is absolutely
> > required, otherwise kmap_local_page() should be preferred.
> > 
> > With kmap_local_page(), the mapping is per thread, CPU local and not
> > globally visible. Furthermore, the mapping can be acquired from any 
context
> > (including interrupts).
> > 
> > Therefore, use kmap_local_page() / kunmap_local() in place of
> > kmap_atomic() / kunmap_atomic().
> > 
> > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> > ---
> >   drivers/android/binder_alloc.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/android/binder_alloc.c b/drivers/android/
binder_alloc.c
> > index 0875c463c002..058595cc7ff0 100644
> > --- a/drivers/android/binder_alloc.c
> > +++ b/drivers/android/binder_alloc.c
> > @@ -1250,17 +1250,17 @@ static int binder_alloc_do_buffer_copy(struct 
binder_alloc *alloc,
> >   		page = binder_alloc_get_page(alloc, buffer,
> >   					     buffer_offset, 
&pgoff);
> >   		size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
> > -		base_ptr = kmap_atomic(page);
> > +		base_ptr = kmap_local_page(page);
> >   		tmpptr = base_ptr + pgoff;
> >   		if (to_buffer)
> >   			memcpy(tmpptr, ptr, size);
> >   		else
> >   			memcpy(ptr, tmpptr, size);
> 
> in the same spirit as patch 1/3, memcpy_to_page() and memcpy_from_page() 
> looks good candidate to avoid code duplication.

Hello Christophe, Todd,

I had thought to use memcpy_to_page() and memcpy_from_page() (exactly as I 
did in other conversions I have been working on during the latest couple of 
weeks). 

However, I decided to avoid to use them for I should also have deleted the 
comment which is before "kunmap_local(base_ptr);".

I don't know how much Maintainers think it is necessary to make readers 
notice that "kunmap_local() takes care of flushing the cache []" (exactly 
as kunmap_atomic() does). Actually I'd delete that comment that looks 
redundant and unnecessary to me, but I cannot know if Todd wants it to 
remain there.

@Todd: Can you please say what you think about this topic? Should I leave 
the patch as-is or I should use memcpy_{to,from}_page() and delete that 
comment?

I won't send any v2 unless I have your confirmation.

Thanks,

Fabio

> 
> Not checked in details, but looks mostly the same.
> 
> Just my 2c.
> 
> CJ
> 
> >   		/*
> > -		 * kunmap_atomic() takes care of flushing the cache
> > +		 * kunmap_local() takes care of flushing the cache
> >   		 * if this device has VIVT cache arch
> >   		 */
> > -		kunmap_atomic(base_ptr);
> > +		kunmap_local(base_ptr);
> >   		bytes -= size;
> >   		pgoff = 0;
> >   		ptr = ptr + size;
> 
> 

Re: [PATCH 3/3] binder: Use kmap_local_page() in binder_alloc_get_page()

[Todd Kjos]

On Sun, Apr 24, 2022 at 2:40 AM Fabio M. De Francesco
<fmdefrancesco@gmail.com> wrote:
>
> On sabato 23 aprile 2022 18:02:48 CEST Christophe JAILLET wrote:
> > Hi,
> >
> > Le 23/04/2022 à 12:24, Fabio M. De Francesco a écrit :
> > > The use of kmap_atomic() is being deprecated in favor of
> kmap_local_page()
> > > where it is feasible. Each call of kmap_atomic() in the kernel creates
> > > a non-preemptible section and disable pagefaults. This could be a
> source
> > > of unwanted latency, so it should be only used if it is absolutely
> > > required, otherwise kmap_local_page() should be preferred.
> > >
> > > With kmap_local_page(), the mapping is per thread, CPU local and not
> > > globally visible. Furthermore, the mapping can be acquired from any
> context
> > > (including interrupts).
> > >
> > > Therefore, use kmap_local_page() / kunmap_local() in place of
> > > kmap_atomic() / kunmap_atomic().
> > >
> > > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> > > ---
> > >   drivers/android/binder_alloc.c | 6 +++---
> > >   1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/android/binder_alloc.c b/drivers/android/
> binder_alloc.c
> > > index 0875c463c002..058595cc7ff0 100644
> > > --- a/drivers/android/binder_alloc.c
> > > +++ b/drivers/android/binder_alloc.c
> > > @@ -1250,17 +1250,17 @@ static int binder_alloc_do_buffer_copy(struct
> binder_alloc *alloc,
> > >             page = binder_alloc_get_page(alloc, buffer,
> > >                                          buffer_offset,
> &pgoff);
> > >             size = min_t(size_t, bytes, PAGE_SIZE - pgoff);
> > > -           base_ptr = kmap_atomic(page);
> > > +           base_ptr = kmap_local_page(page);
> > >             tmpptr = base_ptr + pgoff;
> > >             if (to_buffer)
> > >                     memcpy(tmpptr, ptr, size);
> > >             else
> > >                     memcpy(ptr, tmpptr, size);
> >
> > in the same spirit as patch 1/3, memcpy_to_page() and memcpy_from_page()
> > looks good candidate to avoid code duplication.
>
> Hello Christophe, Todd,
>
> I had thought to use memcpy_to_page() and memcpy_from_page() (exactly as I
> did in other conversions I have been working on during the latest couple of
> weeks).
>
> However, I decided to avoid to use them for I should also have deleted the
> comment which is before "kunmap_local(base_ptr);".
>
> I don't know how much Maintainers think it is necessary to make readers
> notice that "kunmap_local() takes care of flushing the cache []" (exactly
> as kunmap_atomic() does). Actually I'd delete that comment that looks
> redundant and unnecessary to me, but I cannot know if Todd wants it to
> remain there.
>
> @Todd: Can you please say what you think about this topic? Should I leave
> the patch as-is or I should use memcpy_{to,from}_page() and delete that
> comment?

I'm fine with using memcpy_{to,from}_page() and removing the comment.

>
> I won't send any v2 unless I have your confirmation.
>
> Thanks,
>
> Fabio
>
> >
> > Not checked in details, but looks mostly the same.
> >
> > Just my 2c.
> >
> > CJ
> >
> > >             /*
> > > -            * kunmap_atomic() takes care of flushing the cache
> > > +            * kunmap_local() takes care of flushing the cache
> > >              * if this device has VIVT cache arch
> > >              */
> > > -           kunmap_atomic(base_ptr);
> > > +           kunmap_local(base_ptr);
> > >             bytes -= size;
> > >             pgoff = 0;
> > >             ptr = ptr + size;
> >
> >
>
>
>
>