[PATCH net-next v10 1/6] page_pool: fragment API support for 32-bit arch with 64-bit DMA

[PATCH net-next v10 1/6] page_pool: fragment API support for 32-bit arch with 64-bit DMA

[Yunsheng Lin]

Currently page_pool_alloc_frag() is not supported in 32-bit
arch with 64-bit DMA because of the overlap issue between
pp_frag_count and dma_addr_upper in 'struct page' for those
arches, which seems to be quite common, see [1], which means
driver may need to handle it when using fragment API.

It is assumed that the combination of the above arch with an
address space >16TB does not exist, as all those arches have
64b equivalent, it seems logical to use the 64b version for a
system with a large address space. It is also assumed that dma
address is page aligned when we are dma mapping a page aligned
buffer, see [2].

That means we're storing 12 bits of 0 at the lower end for a
dma address, we can reuse those bits for the above arches to
support 32b+12b, which is 16TB of memory.

If we make a wrong assumption, a warning is emitted so that
user can report to us.

1. https://lore.kernel.org/all/20211117075652.58299-1-linyunsheng@huawei.com/
2. https://lore.kernel.org/all/20230818145145.4b357c89@kernel.org/

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
CC: Lorenzo Bianconi <lorenzo@kernel.org>
CC: Alexander Duyck <alexander.duyck@gmail.com>
CC: Liang Chen <liangchen.linux@gmail.com>
CC: Alexander Lobakin <aleksander.lobakin@intel.com>
CC: Guillaume Tucker <guillaume.tucker@collabora.com>
CC: Matthew Wilcox <willy@infradead.org>
CC: Linux-MM <linux-mm@kvack.org>
---
 include/linux/mm_types.h        | 13 +------------
 include/net/page_pool/helpers.h | 20 ++++++++++++++------
 net/core/page_pool.c            | 14 +++++++++-----
 3 files changed, 24 insertions(+), 23 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 36c5b43999e6..74b49c4c7a52 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -125,18 +125,7 @@ struct page {
 			struct page_pool *pp;
 			unsigned long _pp_mapping_pad;
 			unsigned long dma_addr;
-			union {
-				/**
-				 * dma_addr_upper: might require a 64-bit
-				 * value on 32-bit architectures.
-				 */
-				unsigned long dma_addr_upper;
-				/**
-				 * For frag page support, not supported in
-				 * 32-bit architectures with 64-bit DMA.
-				 */
-				atomic_long_t pp_frag_count;
-			};
+			atomic_long_t pp_frag_count;
 		};
 		struct {	/* Tail pages of compound page */
 			unsigned long compound_head;	/* Bit zero is set */
diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
index 94231533a369..8e1c85de4995 100644
--- a/include/net/page_pool/helpers.h
+++ b/include/net/page_pool/helpers.h
@@ -197,7 +197,7 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
 	page_pool_put_full_page(pool, page, true);
 }
 
-#define PAGE_POOL_DMA_USE_PP_FRAG_COUNT	\
+#define PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA	\
 		(sizeof(dma_addr_t) > sizeof(unsigned long))
 
 /**
@@ -211,17 +211,25 @@ static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
 {
 	dma_addr_t ret = page->dma_addr;
 
-	if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
-		ret |= (dma_addr_t)page->dma_addr_upper << 16 << 16;
+	if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA)
+		ret <<= PAGE_SHIFT;
 
 	return ret;
 }
 
-static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
+static inline bool page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
 {
+	if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA) {
+		page->dma_addr = addr >> PAGE_SHIFT;
+
+		/* We assume page alignment to shave off bottom bits,
+		 * if this "compression" doesn't work we need to drop.
+		 */
+		return addr != (dma_addr_t)page->dma_addr << PAGE_SHIFT;
+	}
+
 	page->dma_addr = addr;
-	if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
-		page->dma_addr_upper = upper_32_bits(addr);
+	return false;
 }
 
 static inline bool page_pool_put(struct page_pool *pool)
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 77cb75e63aca..8a9868ea5067 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -211,10 +211,6 @@ static int page_pool_init(struct page_pool *pool,
 		 */
 	}
 
-	if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT &&
-	    pool->p.flags & PP_FLAG_PAGE_FRAG)
-		return -EINVAL;
-
 #ifdef CONFIG_PAGE_POOL_STATS
 	pool->recycle_stats = alloc_percpu(struct page_pool_recycle_stats);
 	if (!pool->recycle_stats)
@@ -359,12 +355,20 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
 	if (dma_mapping_error(pool->p.dev, dma))
 		return false;
 
-	page_pool_set_dma_addr(page, dma);
+	if (page_pool_set_dma_addr(page, dma))
+		goto unmap_failed;
 
 	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
 		page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
 
 	return true;
+
+unmap_failed:
+	WARN_ON_ONCE("unexpected DMA address, please report to netdev@");
+	dma_unmap_page_attrs(pool->p.dev, dma,
+			     PAGE_SIZE << pool->p.order, pool->p.dma_dir,
+			     DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WEAK_ORDERING);
+	return false;
 }
 
 static void page_pool_set_pp_info(struct page_pool *pool,
-- 
2.33.0

Re: [PATCH net-next v10 1/6] page_pool: fragment API support for 32-bit arch with 64-bit DMA

[Paolo Abeni]

On Fri, 2023-09-22 at 17:11 +0800, Yunsheng Lin wrote:
> Currently page_pool_alloc_frag() is not supported in 32-bit
> arch with 64-bit DMA because of the overlap issue between
> pp_frag_count and dma_addr_upper in 'struct page' for those
> arches, which seems to be quite common, see [1], which means
> driver may need to handle it when using fragment API.
> 
> It is assumed that the combination of the above arch with an
> address space >16TB does not exist, as all those arches have
> 64b equivalent, it seems logical to use the 64b version for a
> system with a large address space. It is also assumed that dma
> address is page aligned when we are dma mapping a page aligned
> buffer, see [2].
> 
> That means we're storing 12 bits of 0 at the lower end for a
> dma address, we can reuse those bits for the above arches to
> support 32b+12b, which is 16TB of memory.
> 
> If we make a wrong assumption, a warning is emitted so that
> user can report to us.
> 
> 1. https://lore.kernel.org/all/20211117075652.58299-1-linyunsheng@huawei.com/
> 2. https://lore.kernel.org/all/20230818145145.4b357c89@kernel.org/
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> CC: Lorenzo Bianconi <lorenzo@kernel.org>
> CC: Alexander Duyck <alexander.duyck@gmail.com>
> CC: Liang Chen <liangchen.linux@gmail.com>
> CC: Alexander Lobakin <aleksander.lobakin@intel.com>
> CC: Guillaume Tucker <guillaume.tucker@collabora.com>
> CC: Matthew Wilcox <willy@infradead.org>
> CC: Linux-MM <linux-mm@kvack.org>
> ---
>  include/linux/mm_types.h        | 13 +------------
>  include/net/page_pool/helpers.h | 20 ++++++++++++++------
>  net/core/page_pool.c            | 14 +++++++++-----
>  3 files changed, 24 insertions(+), 23 deletions(-)
> 
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 36c5b43999e6..74b49c4c7a52 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -125,18 +125,7 @@ struct page {
>  			struct page_pool *pp;
>  			unsigned long _pp_mapping_pad;
>  			unsigned long dma_addr;
> -			union {
> -				/**
> -				 * dma_addr_upper: might require a 64-bit
> -				 * value on 32-bit architectures.
> -				 */
> -				unsigned long dma_addr_upper;
> -				/**
> -				 * For frag page support, not supported in
> -				 * 32-bit architectures with 64-bit DMA.
> -				 */
> -				atomic_long_t pp_frag_count;
> -			};
> +			atomic_long_t pp_frag_count;
>  		};
>  		struct {	/* Tail pages of compound page */
>  			unsigned long compound_head;	/* Bit zero is set */

As noted by Jesper, since this is touching the super-critcal struct
page, an explicit ack from the mm people is required.

@Matthew: could you please have a look?

I think it would be nice also an explicit ack from Jesper and/or Ilias.

Cheers,

Paolo

Re: [PATCH net-next v10 1/6] page_pool: fragment API support for 32-bit arch with 64-bit DMA

[Ilias Apalodimas]

Hi Paolo

On Tue, 3 Oct 2023 at 10:46, Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Fri, 2023-09-22 at 17:11 +0800, Yunsheng Lin wrote:
> > Currently page_pool_alloc_frag() is not supported in 32-bit
> > arch with 64-bit DMA because of the overlap issue between
> > pp_frag_count and dma_addr_upper in 'struct page' for those
> > arches, which seems to be quite common, see [1], which means
> > driver may need to handle it when using fragment API.
> >
> > It is assumed that the combination of the above arch with an
> > address space >16TB does not exist, as all those arches have
> > 64b equivalent, it seems logical to use the 64b version for a
> > system with a large address space. It is also assumed that dma
> > address is page aligned when we are dma mapping a page aligned
> > buffer, see [2].
> >
> > That means we're storing 12 bits of 0 at the lower end for a
> > dma address, we can reuse those bits for the above arches to
> > support 32b+12b, which is 16TB of memory.
> >
> > If we make a wrong assumption, a warning is emitted so that
> > user can report to us.
> >
> > 1. https://lore.kernel.org/all/20211117075652.58299-1-linyunsheng@huawei.com/
> > 2. https://lore.kernel.org/all/20230818145145.4b357c89@kernel.org/
> >
> > Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> > Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> > CC: Lorenzo Bianconi <lorenzo@kernel.org>
> > CC: Alexander Duyck <alexander.duyck@gmail.com>
> > CC: Liang Chen <liangchen.linux@gmail.com>
> > CC: Alexander Lobakin <aleksander.lobakin@intel.com>
> > CC: Guillaume Tucker <guillaume.tucker@collabora.com>
> > CC: Matthew Wilcox <willy@infradead.org>
> > CC: Linux-MM <linux-mm@kvack.org>
> > ---
> >  include/linux/mm_types.h        | 13 +------------
> >  include/net/page_pool/helpers.h | 20 ++++++++++++++------
> >  net/core/page_pool.c            | 14 +++++++++-----
> >  3 files changed, 24 insertions(+), 23 deletions(-)
> >
> > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > index 36c5b43999e6..74b49c4c7a52 100644
> > --- a/include/linux/mm_types.h
> > +++ b/include/linux/mm_types.h
> > @@ -125,18 +125,7 @@ struct page {
> >                       struct page_pool *pp;
> >                       unsigned long _pp_mapping_pad;
> >                       unsigned long dma_addr;
> > -                     union {
> > -                             /**
> > -                              * dma_addr_upper: might require a 64-bit
> > -                              * value on 32-bit architectures.
> > -                              */
> > -                             unsigned long dma_addr_upper;
> > -                             /**
> > -                              * For frag page support, not supported in
> > -                              * 32-bit architectures with 64-bit DMA.
> > -                              */
> > -                             atomic_long_t pp_frag_count;
> > -                     };
> > +                     atomic_long_t pp_frag_count;
> >               };
> >               struct {        /* Tail pages of compound page */
> >                       unsigned long compound_head;    /* Bit zero is set */
>
> As noted by Jesper, since this is touching the super-critcal struct
> page, an explicit ack from the mm people is required.
>
> @Matthew: could you please have a look?
>
> I think it would be nice also an explicit ack from Jesper and/or Ilias.

I am trying! Unfortunately, it's this time of the year when I have to
travel a lot.  I'll be back in 15 days from now and I will be able to
have a look

Thanks and sorry for the delay
/Ilias

>
> Cheers,
>
> Paolo
>

Re: [PATCH net-next v10 1/6] page_pool: fragment API support for 32-bit arch with 64-bit DMA

[Jakub Kicinski]

On Tue, 03 Oct 2023 09:45:56 +0200 Paolo Abeni wrote:
> I think it would be nice also an explicit ack from Jesper and/or Ilias.

Also a review tag from one or both of the Alexanders would be great!

Re: [PATCH net-next v10 1/6] page_pool: fragment API support for 32-bit arch with 64-bit DMA

[Alexander Lobakin]

From: Jakub Kicinski <kuba@kernel.org>
Date: Tue, 3 Oct 2023 15:12:16 -0700

> On Tue, 03 Oct 2023 09:45:56 +0200 Paolo Abeni wrote:
>> I think it would be nice also an explicit ack from Jesper and/or Ilias.
> 
> Also a review tag from one or both of the Alexanders would be great!

I got back to libie/iavf this week, hoping I'll rebase without major
issues and will be able to give a Tested-by as well, will see :>

Thanks,
Olek

Re: [PATCH net-next v10 1/6] page_pool: fragment API support for 32-bit arch with 64-bit DMA

[Yunsheng Lin]

On 2023/10/4 17:31, Alexander Lobakin wrote:
> From: Jakub Kicinski <kuba@kernel.org>
> Date: Tue, 3 Oct 2023 15:12:16 -0700
> 
>> On Tue, 03 Oct 2023 09:45:56 +0200 Paolo Abeni wrote:
>>> I think it would be nice also an explicit ack from Jesper and/or Ilias.
>>
>> Also a review tag from one or both of the Alexanders would be great!
> 
> I got back to libie/iavf this week, hoping I'll rebase without major
> issues and will be able to give a Tested-by as well, will see :>
>

It is great to have some Tested-by tag to confirm that this patchset
works for other driver. Please let me know if there is any problem when
rebasing and testing, thanks.


> Thanks,
> Olek
> 
> .
> 

Re: [PATCH net-next v10 1/6] page_pool: fragment API support for 32-bit arch with 64-bit DMA

[Alexander Lobakin]

From: Yunsheng Lin <linyunsheng@huawei.com>
Date: Sun, 8 Oct 2023 17:36:59 +0800

> On 2023/10/4 17:31, Alexander Lobakin wrote:
>> From: Jakub Kicinski <kuba@kernel.org>
>> Date: Tue, 3 Oct 2023 15:12:16 -0700
>>
>>> On Tue, 03 Oct 2023 09:45:56 +0200 Paolo Abeni wrote:
>>>> I think it would be nice also an explicit ack from Jesper and/or Ilias.
>>>
>>> Also a review tag from one or both of the Alexanders would be great!
>>
>> I got back to libie/iavf this week, hoping I'll rebase without major
>> issues and will be able to give a Tested-by as well, will see :>
>>
> 
> It is great to have some Tested-by tag to confirm that this patchset
> works for other driver. Please let me know if there is any problem when
> rebasing and testing, thanks.

IAVF with PP on the latest net-next from [0]:

Tested-by: Alexander Lobakin <aleksander.lobakin@intel.com>

Still some stuff on my side to fix/improve before submitting a new
revision of libie / PP for IAVF, but at least the current code works
just as expected.

> 
> 
>> Thanks,
>> Olek
>>
>> .
>>

[0] https://github.com/alobakin/linux/commits/iavf-pp-frag

Thanks,
Olek