[RFC mm v4 1/2] page_pool: check if nmdesc->pp is !NULL to confirm its usage as pp for net_iov
From: Byungchul Park <byungchul@sk.com>
Date: 2025-10-23 07:44:27
Also in:
bpf, linux-mm, linux-rdma, lkml
Subsystem:
networking [general], page pool, the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Jesper Dangaard Brouer, Ilias Apalodimas, Linus Torvalds
->pp_magic field in struct page is current used to identify if a page belongs to a page pool. However, ->pp_magic will be removed and page type bit in struct page e.g. PGTY_netpp should be used for that purpose. As a preparation, the check for net_iov, that is not page-backed, should avoid using ->pp_magic since net_iov doens't have to do with page type. Instead, nmdesc->pp can be used if a net_iov or its nmdesc belongs to a page pool, by making sure nmdesc->pp is NULL otherwise. For page-backed netmem, just leave unchanged as is, while for net_iov, make sure nmdesc->pp is initialized to NULL and use nmdesc->pp for the check. Signed-off-by: Byungchul Park <byungchul@sk.com> --- net/core/devmem.c | 1 + net/core/netmem_priv.h | 8 ++++++++ net/core/page_pool.c | 16 ++++++++++++++-- 3 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/net/core/devmem.c b/net/core/devmem.c
index d9de31a6cc7f..f81b700f1fd1 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c@@ -291,6 +291,7 @@ net_devmem_bind_dmabuf(struct net_device *dev, niov = &owner->area.niovs[i]; niov->type = NET_IOV_DMABUF; niov->owner = &owner->area; + niov->desc.pp = NULL; page_pool_set_dma_addr_netmem(net_iov_to_netmem(niov), net_devmem_get_dma_addr(niov)); if (direction == DMA_TO_DEVICE)
diff --git a/net/core/netmem_priv.h b/net/core/netmem_priv.h
index 23175cb2bd86..5561fd556bc5 100644
--- a/net/core/netmem_priv.h
+++ b/net/core/netmem_priv.h@@ -22,6 +22,14 @@ static inline void netmem_clear_pp_magic(netmem_ref netmem) static inline bool netmem_is_pp(netmem_ref netmem) { + /* net_iov may be part of a page pool. For net_iov, ->pp in + * net_iov.desc can be used to determine if the pages belong to + * a page pool. Ensure that the ->pp either points to its page + * pool or is set to NULL if it does not. + */ + if (netmem_is_net_iov(netmem)) + return !!netmem_to_nmdesc(netmem)->pp; + return (netmem_get_pp_magic(netmem) & PP_MAGIC_MASK) == PP_SIGNATURE; }
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 1a5edec485f1..2756b78754b0 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c@@ -699,7 +699,13 @@ s32 page_pool_inflight(const struct page_pool *pool, bool strict) void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem) { netmem_set_pp(netmem, pool); - netmem_or_pp_magic(netmem, PP_SIGNATURE); + + /* For page-backed, pp_magic is used to identify if it's pp. + * For net_iov, it's ensured nmdesc->pp is non-NULL if it's pp + * and nmdesc->pp is NULL if it's not. + */ + if (!netmem_is_net_iov(netmem)) + netmem_or_pp_magic(netmem, PP_SIGNATURE); /* Ensuring all pages have been split into one fragment initially: * page_pool_set_pp_info() is only called once for every page when it
@@ -714,7 +720,13 @@ void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem) void page_pool_clear_pp_info(netmem_ref netmem) { - netmem_clear_pp_magic(netmem); + /* For page-backed, pp_magic is used to identify if it's pp. + * For net_iov, it's ensured nmdesc->pp is non-NULL if it's pp + * and nmdesc->pp is NULL if it's not. + */ + if (!netmem_is_net_iov(netmem)) + netmem_clear_pp_magic(netmem); + netmem_set_pp(netmem, NULL); }
--
2.17.1