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Date: Wed, 20 Sep 2023 16:59:04 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Jesper Dangaard Brouer <jbrouer@...hat.com>, <davem@...emloft.net>,
<kuba@...nel.org>, <pabeni@...hat.com>
CC: <brouer@...hat.com>, <netdev@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, Lorenzo Bianconi <lorenzo@...nel.org>,
Alexander Duyck <alexander.duyck@...il.com>, Liang Chen
<liangchen.linux@...il.com>, Alexander Lobakin
<aleksander.lobakin@...el.com>, Guillaume Tucker
<guillaume.tucker@...labora.com>, Jesper Dangaard Brouer <hawk@...nel.org>,
Ilias Apalodimas <ilias.apalodimas@...aro.org>, Eric Dumazet
<edumazet@...gle.com>, Linux-MM <linux-mm@...ck.org>, Matthew Wilcox
<willy@...radead.org>, Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH net-next v8 1/6] page_pool: frag API support for 32-bit
arch with 64-bit DMA
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@...ck.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@...nel.org>
>> Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
>> CC: Lorenzo Bianconi <lorenzo@...nel.org>
>> CC: Alexander Duyck <alexander.duyck@...il.com>
>> CC: Liang Chen <liangchen.linux@...il.com>
>> CC: Alexander Lobakin <aleksander.lobakin@...el.com>
>> CC: Guillaume Tucker <guillaume.tucker@...labora.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,
>
> .
>
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