[net-next PATCH V2 0/3] Fix page_pool API and dma address storage

[net-next PATCH V2 0/3] Fix page_pool API and dma address storage

[Jesper Dangaard Brouer]

As pointed out by David Miller in [1] the current page_pool implementation
stores dma_addr_t in page->private. This won't work on 32-bit platforms with
64-bit DMA addresses since the page->private is an unsigned long and the
dma_addr_t a u64.

Since no driver is yet using the DMA mapping capabilities of the API let's
fix this by storing the information in 'struct page' and use that to store
and retrieve DMA addresses from network drivers.

As long as the addresses returned from dma_map_page() are aligned the first
bit, used by the compound pages code should not be set.

Ilias tested this on Espressobin driver mvneta, for which we have patches
for using the DMA API of page_pool.

[1]: https://lore.kernel.org/netdev/20181207.230655.1261252486319967024.davem@davemloft.net/

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
---

Ilias Apalodimas (1):
      net: page_pool: don't use page->private to store dma_addr_t

Jesper Dangaard Brouer (2):
      mm: add dma_addr_t to struct page
      page_pool: use DMA_ATTR_SKIP_CPU_SYNC for DMA mappings


 include/linux/mm_types.h |    7 +++++++
 net/core/page_pool.c     |   22 ++++++++++++++--------
 2 files changed, 21 insertions(+), 8 deletions(-)

--

[net-next PATCH V2 1/3] mm: add dma_addr_t to struct page

[Jesper Dangaard Brouer]

The page_pool API is using page->private to store DMA addresses.
As pointed out by David Miller we can't use that on 32-bit architectures
with 64-bit DMA

This patch adds a new dma_addr_t struct to allow storing DMA addresses

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
---
 include/linux/mm_types.h |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 2c471a2c43fa..581737bd0878 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -95,6 +95,13 @@ struct page {
 			 */
 			unsigned long private;
 		};
+		struct {	/* page_pool used by netstack */
+			/**
+			 * @dma_addr: page_pool requires a 64-bit value even on
+			 * 32-bit architectures.
+			 */
+			dma_addr_t dma_addr;
+		};
 		struct {	/* slab, slob and slub */
 			union {
 				struct list_head slab_list;	/* uses lru */

[net-next PATCH V2 2/3] net: page_pool: don't use page->private to store dma_addr_t

[Jesper Dangaard Brouer]

From: Ilias Apalodimas <ilias.apalodimas@linaro.org>

As pointed out by David Miller the current page_pool implementation
stores dma_addr_t in page->private.
This won't work on 32-bit platforms with 64-bit DMA addresses since the
page->private is an unsigned long and the dma_addr_t a u64.

A previous patch is adding dma_addr_t on struct page to accommodate this.
This patch adapts the page_pool related functions to use the newly added
struct for storing and retrieving DMA addresses from network drivers.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 net/core/page_pool.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 43a932cb609b..897a69a1477e 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -136,7 +136,9 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
 		goto skip_dma_map;
 
-	/* Setup DMA mapping: use page->private for DMA-addr
+	/* Setup DMA mapping: use 'struct page' area for storing DMA-addr
+	 * since dma_addr_t can be either 32 or 64 bits and does not always fit
+	 * into page private data (i.e 32bit cpu with 64bit DMA caps)
 	 * This mapping is kept for lifetime of page, until leaving pool.
 	 */
 	dma = dma_map_page(pool->p.dev, page, 0,
@@ -146,7 +148,7 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 		put_page(page);
 		return NULL;
 	}
-	set_page_private(page, dma); /* page->private = dma; */
+	page->dma_addr = dma;
 
 skip_dma_map:
 	/* When page just alloc'ed is should/must have refcnt 1. */
@@ -175,13 +177,16 @@ EXPORT_SYMBOL(page_pool_alloc_pages);
 static void __page_pool_clean_page(struct page_pool *pool,
 				   struct page *page)
 {
+	dma_addr_t dma;
+
 	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
 		return;
 
+	dma = page->dma_addr;
 	/* DMA unmap */
-	dma_unmap_page(pool->p.dev, page_private(page),
+	dma_unmap_page(pool->p.dev, dma,
 		       PAGE_SIZE << pool->p.order, pool->p.dma_dir);
-	set_page_private(page, 0);
+	page->dma_addr = 0;
 }
 
 /* Return a page to the page allocator, cleaning up our state */

[net-next PATCH V2 3/3] page_pool: use DMA_ATTR_SKIP_CPU_SYNC for DMA mappings

[Jesper Dangaard Brouer]

As pointed out by Alexander Duyck, the DMA mapping done in page_pool needs
to use the DMA attribute DMA_ATTR_SKIP_CPU_SYNC.

As the principle behind page_pool keeping the pages mapped is that the
driver takes over the DMA-sync steps.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
---
 net/core/page_pool.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 897a69a1477e..7e624c2cd709 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -141,9 +141,9 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
 	 * into page private data (i.e 32bit cpu with 64bit DMA caps)
 	 * This mapping is kept for lifetime of page, until leaving pool.
 	 */
-	dma = dma_map_page(pool->p.dev, page, 0,
-			   (PAGE_SIZE << pool->p.order),
-			   pool->p.dma_dir);
+	dma = dma_map_page_attrs(pool->p.dev, page, 0,
+				 (PAGE_SIZE << pool->p.order),
+				 pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
 	if (dma_mapping_error(pool->p.dev, dma)) {
 		put_page(page);
 		return NULL;
@@ -184,8 +184,9 @@ static void __page_pool_clean_page(struct page_pool *pool,
 
 	dma = page->dma_addr;
 	/* DMA unmap */
-	dma_unmap_page(pool->p.dev, dma,
-		       PAGE_SIZE << pool->p.order, pool->p.dma_dir);
+	dma_unmap_page_attr(pool->p.dev, dma,
+			    PAGE_SIZE << pool->p.order, pool->p.dma_dir,
+			    DMA_ATTR_SKIP_CPU_SYNC);
 	page->dma_addr = 0;
 }
 

Re: [net-next PATCH V2 3/3] page_pool: use DMA_ATTR_SKIP_CPU_SYNC for DMA mappings

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 1681 bytes --]

Hi Jesper,

I love your patch! Yet something to improve:

[auto build test ERROR on net-next/master]

url:    https://github.com/0day-ci/linux/commits/Jesper-Dangaard-Brouer/mm-add-dma_addr_t-to-struct-page/20190213-002150
config: ia64-allyesconfig (attached as .config)
compiler: ia64-linux-gcc (GCC) 8.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=8.2.0 make.cross ARCH=ia64 

All errors (new ones prefixed by >>):

   net/core/page_pool.c: In function '__page_pool_clean_page':
>> net/core/page_pool.c:187:2: error: implicit declaration of function 'dma_unmap_page_attr'; did you mean 'dma_unmap_page_attrs'? [-Werror=implicit-function-declaration]
     dma_unmap_page_attr(pool->p.dev, dma,
     ^~~~~~~~~~~~~~~~~~~
     dma_unmap_page_attrs
   cc1: some warnings being treated as errors

vim +187 net/core/page_pool.c

   175	
   176	/* Cleanup page_pool state from page */
   177	static void __page_pool_clean_page(struct page_pool *pool,
   178					   struct page *page)
   179	{
   180		dma_addr_t dma;
   181	
   182		if (!(pool->p.flags & PP_FLAG_DMA_MAP))
   183			return;
   184	
   185		dma = page->dma_addr;
   186		/* DMA unmap */
 > 187		dma_unmap_page_attr(pool->p.dev, dma,
   188				    PAGE_SIZE << pool->p.order, pool->p.dma_dir,
   189				    DMA_ATTR_SKIP_CPU_SYNC);
   190		page->dma_addr = 0;
   191	}
   192	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 56263 bytes --]

Re: [net-next PATCH V2 3/3] page_pool: use DMA_ATTR_SKIP_CPU_SYNC for DMA mappings

[Jesper Dangaard Brouer]

On Wed, 13 Feb 2019 01:12:59 +0800
kbuild test robot <lkp@intel.com> wrote:

>    net/core/page_pool.c: In function '__page_pool_clean_page':
> >> net/core/page_pool.c:187:2: error: implicit declaration of function 'dma_unmap_page_attr'; did you mean 'dma_unmap_page_attrs'? [-Werror=implicit-function-declaration]  
>      dma_unmap_page_attr(pool->p.dev, dma,
>      ^~~~~~~~~~~~~~~~~~~
>      dma_unmap_page_attrs
>    cc1: some warnings being treated as errors

Ups, in my compile test I didn't have CONFIG_PAGE_POOL defined.
Will respin a V3.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

Re: [net-next PATCH V2 1/3] mm: add dma_addr_t to struct page

[Florian Fainelli]

On 2/12/19 6:49 AM, Jesper Dangaard Brouer wrote:
> The page_pool API is using page->private to store DMA addresses.
> As pointed out by David Miller we can't use that on 32-bit architectures
> with 64-bit DMA
> 
> This patch adds a new dma_addr_t struct to allow storing DMA addresses
> 
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> Acked-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>  include/linux/mm_types.h |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 2c471a2c43fa..581737bd0878 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -95,6 +95,13 @@ struct page {
>  			 */
>  			unsigned long private;
>  		};
> +		struct {	/* page_pool used by netstack */
> +			/**
> +			 * @dma_addr: page_pool requires a 64-bit value even on
> +			 * 32-bit architectures.
> +			 */

Nit: might require? dma_addr_t, as you mention in the commit may have a
different size based on CONFIG_ARCH_DMA_ADDR_T_64BIT.
-- 
Florian

Re: [net-next PATCH V2 1/3] mm: add dma_addr_t to struct page

[Jesper Dangaard Brouer]

On Tue, 12 Feb 2019 10:05:39 -0800
Florian Fainelli <f.fainelli@gmail.com> wrote:

> On 2/12/19 6:49 AM, Jesper Dangaard Brouer wrote:
> > The page_pool API is using page->private to store DMA addresses.
> > As pointed out by David Miller we can't use that on 32-bit architectures
> > with 64-bit DMA
> > 
> > This patch adds a new dma_addr_t struct to allow storing DMA addresses
> > 
> > Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> > Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> > Acked-by: Andrew Morton <akpm@linux-foundation.org>
> > ---
> >  include/linux/mm_types.h |    7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > index 2c471a2c43fa..581737bd0878 100644
> > --- a/include/linux/mm_types.h
> > +++ b/include/linux/mm_types.h
> > @@ -95,6 +95,13 @@ struct page {
> >  			 */
> >  			unsigned long private;
> >  		};
> > +		struct {	/* page_pool used by netstack */
> > +			/**
> > +			 * @dma_addr: page_pool requires a 64-bit value even on
> > +			 * 32-bit architectures.
> > +			 */  
> 
> Nit: might require? dma_addr_t, as you mention in the commit may have a
> different size based on CONFIG_ARCH_DMA_ADDR_T_64BIT.

So you want me to change the comment to be:

/**
 * @dma_addr: might require a 64-bit value even on
 * 32-bit architectures.
 */

Correctly understood?
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

Re: [net-next PATCH V2 1/3] mm: add dma_addr_t to struct page

[Florian Fainelli]

On 2/12/19 10:19 AM, Jesper Dangaard Brouer wrote:
> On Tue, 12 Feb 2019 10:05:39 -0800
> Florian Fainelli <f.fainelli@gmail.com> wrote:
> 
>> On 2/12/19 6:49 AM, Jesper Dangaard Brouer wrote:
>>> The page_pool API is using page->private to store DMA addresses.
>>> As pointed out by David Miller we can't use that on 32-bit architectures
>>> with 64-bit DMA
>>>
>>> This patch adds a new dma_addr_t struct to allow storing DMA addresses
>>>
>>> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
>>> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
>>> Acked-by: Andrew Morton <akpm@linux-foundation.org>
>>> ---
>>>  include/linux/mm_types.h |    7 +++++++
>>>  1 file changed, 7 insertions(+)
>>>
>>> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
>>> index 2c471a2c43fa..581737bd0878 100644
>>> --- a/include/linux/mm_types.h
>>> +++ b/include/linux/mm_types.h
>>> @@ -95,6 +95,13 @@ struct page {
>>>  			 */
>>>  			unsigned long private;
>>>  		};
>>> +		struct {	/* page_pool used by netstack */
>>> +			/**
>>> +			 * @dma_addr: page_pool requires a 64-bit value even on
>>> +			 * 32-bit architectures.
>>> +			 */  
>>
>> Nit: might require? dma_addr_t, as you mention in the commit may have a
>> different size based on CONFIG_ARCH_DMA_ADDR_T_64BIT.
> 
> So you want me to change the comment to be:
> 
> /**
>  * @dma_addr: might require a 64-bit value even on
>  * 32-bit architectures.
>  */
> 
> Correctly understood?

Correct, that is what I would change. The commit message is correct, but
the comment makes it sound like dma_addr_t is guaranteed to be 64-bit,
while it is actually platform dependent. Does that make it clearer?
-- 
Florian