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 frag 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 aliged
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>
---
 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

Hi Lin,

This looks reasonable, but given you are changing struct-page
(include/linux/mm_types.h) we need to MM-list <linux-mm@kvack.org>.
Also Cc Wilcox.

I think it was Ilias and Duyck that validated the assumptions, last time
this patch was discussed. Thus I want to see their review before this is
applied.

-Jesper

On 12/09/2023 10.31, 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 frag 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 aliged
> 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>
> ---
>   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,

On 2023/9/15 16:28, Jesper Dangaard Brouer wrote:
> Hi Lin,
> 
> This looks reasonable, but given you are changing struct-page
> (include/linux/mm_types.h) we need to MM-list <linux-mm@kvack.org>.
> Also Cc Wilcox.
> 
> I think it was Ilias and Duyck that validated the assumptions, last time
> this patch was discussed. Thus I want to see their review before this is
> applied.

FWIW, PAGE_SIZE aligned buffer being PAGE_SIZE aligned in DMA is
validated by Duyck:
https://lore.kernel.org/all/CAKgT0UfeUAUQpEffxnkc+gzXsjOrHkuMgxU_Aw0VXSJYKzaovQ@mail.gmail.com/

And I had done researching to find out there seems to be no combination of
the above arch with an address space >16TB:
https://lore.kernel.org/all/2b570282-24f8-f23b-1ff7-ad836794baa9@huawei.com/

> 
> -Jesper
> 
> On 12/09/2023 10.31, 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 frag 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 aliged
>> 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>
>> ---
>>   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,
> 
> .
>

Hi

On Wed, 20 Sept 2023 at 11:59, Yunsheng Lin <linyunsheng@huawei.com> wrote:
>
> On 2023/9/15 16:28, Jesper Dangaard Brouer wrote:
> > Hi Lin,
> >
> > This looks reasonable, but given you are changing struct-page
> > (include/linux/mm_types.h) we need to MM-list <linux-mm@kvack.org>.
> > Also Cc Wilcox.
> >
> > I think it was Ilias and Duyck that validated the assumptions, last time
> > this patch was discussed. Thus I want to see their review before this is
> > applied.
>
> FWIW, PAGE_SIZE aligned buffer being PAGE_SIZE aligned in DMA is
> validated by Duyck:
> https://lore.kernel.org/all/CAKgT0UfeUAUQpEffxnkc+gzXsjOrHkuMgxU_Aw0VXSJYKzaovQ@mail.gmail.com/
>
> And I had done researching to find out there seems to be no combination of
> the above arch with an address space >16TB:
> https://lore.kernel.org/all/2b570282-24f8-f23b-1ff7-ad836794baa9@huawei.com/

Apologies for the late reply.  I just saw you sent a v9, I'll review
that instead, but I am traveling right now, will take a while

Thanks
/Ilias
>
> >
> > -Jesper
> >
> > On 12/09/2023 10.31, 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 frag 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 aliged
> >> 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>
> >> ---
> >>   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,
> >
> > .
> >

On 2023/9/25 18:37, Ilias Apalodimas wrote:
> Hi
> 
> On Wed, 20 Sept 2023 at 11:59, Yunsheng Lin <linyunsheng@huawei.com> wrote:
>>
>> On 2023/9/15 16:28, Jesper Dangaard Brouer wrote:
>>> Hi Lin,
>>>
>>> This looks reasonable, but given you are changing struct-page
>>> (include/linux/mm_types.h) we need to MM-list <linux-mm@kvack.org>.
>>> Also Cc Wilcox.
>>>
>>> I think it was Ilias and Duyck that validated the assumptions, last time
>>> this patch was discussed. Thus I want to see their review before this is
>>> applied.
>>
>> FWIW, PAGE_SIZE aligned buffer being PAGE_SIZE aligned in DMA is
>> validated by Duyck:
>> https://lore.kernel.org/all/CAKgT0UfeUAUQpEffxnkc+gzXsjOrHkuMgxU_Aw0VXSJYKzaovQ@mail.gmail.com/
>>
>> And I had done researching to find out there seems to be no combination of
>> the above arch with an address space >16TB:
>> https://lore.kernel.org/all/2b570282-24f8-f23b-1ff7-ad836794baa9@huawei.com/
> 
> Apologies for the late reply.  I just saw you sent a v9, I'll review
> that instead, but I am traveling right now, will take a while

Actually there is a newer v10, see:
https://lore.kernel.org/all/20230922091138.18014-2-linyunsheng@huawei.com/

Thanks for the time reviewing.

> 
> Thanks
> /Ilias