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SubjectRe: [PATCH net] page_pool: Revert "page_pool: disable dma mapping support..."
On Wed, 17 Nov 2021 at 13:48, Jesper Dangaard Brouer <jbrouer@redhat.com> wrote:
>
> Added CC: linux-mm@kvack.org
>
> On 17/11/2021 08.56, Yunsheng Lin wrote:
> > This reverts commit d00e60ee54b12de945b8493cf18c1ada9e422514.
> >
> > As reported by Guillaume in [1]:
> > Enabling LPAE always enables CONFIG_ARCH_DMA_ADDR_T_64BIT
> > in 32-bit systems, which breaks the bootup proceess when a
> > ethernet driver is using page pool with PP_FLAG_DMA_MAP flag.
> > As we were hoping we had no active consumers for such system
> > when we removed the dma mapping support, and LPAE seems like
> > a common feature for 32 bits system, so revert it.
> >
> > 1. https://www.spinics.net/lists/netdev/msg779890.html
> >
> > Fixes: d00e60ee54b1 ("page_pool: disable dma mapping support for 32-bit arch with 64-bit DMA")
> > Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> > ---
> > include/linux/mm_types.h | 13 ++++++++++++-
> > include/net/page_pool.h | 12 +++++++++++-
> > net/core/page_pool.c | 10 ++++------
> > 3 files changed, 27 insertions(+), 8 deletions(-)
>
> Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
>
> Too bad that we have to keep this code-uglyness in struct page, and
> handling in page_pool.

Indeed :(

Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
>
>
> > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > index bb8c6f5f19bc..c3a6e6209600 100644
> > --- a/include/linux/mm_types.h
> > +++ b/include/linux/mm_types.h
> > @@ -105,7 +105,18 @@ struct page {
> > struct page_pool *pp;
> > unsigned long _pp_mapping_pad;
> > unsigned long dma_addr;
> > - atomic_long_t pp_frag_count;
> > + 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;
> > + };
> > };
> > struct { /* slab, slob and slub */
> > union {
> > diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> > index 3855f069627f..a4082406a003 100644
> > --- a/include/net/page_pool.h
> > +++ b/include/net/page_pool.h
> > @@ -216,14 +216,24 @@ 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 \
> > + (sizeof(dma_addr_t) > sizeof(unsigned long))
> > +
> > static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
> > {
> > - return page->dma_addr;
> > + 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;
> > +
> > + return ret;
> > }
> >
> > static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
> > {
> > page->dma_addr = addr;
> > + if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
> > + page->dma_addr_upper = upper_32_bits(addr);
> > }
> >
> > static inline void page_pool_set_frag_count(struct page *page, long nr)
> > diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> > index 9b60e4301a44..1a6978427d6c 100644
> > --- a/net/core/page_pool.c
> > +++ b/net/core/page_pool.c
> > @@ -49,12 +49,6 @@ static int page_pool_init(struct page_pool *pool,
> > * which is the XDP_TX use-case.
> > */
> > if (pool->p.flags & PP_FLAG_DMA_MAP) {
> > - /* DMA-mapping is not supported on 32-bit systems with
> > - * 64-bit DMA mapping.
> > - */
> > - if (sizeof(dma_addr_t) > sizeof(unsigned long))
> > - return -EOPNOTSUPP;
> > -
> > if ((pool->p.dma_dir != DMA_FROM_DEVICE) &&
> > (pool->p.dma_dir != DMA_BIDIRECTIONAL))
> > return -EINVAL;
> > @@ -75,6 +69,10 @@ 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;
> > +
> > if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
> > return -ENOMEM;
> >
> >
>

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