From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7F10D371043; Mon, 12 Oct 2026 13:34:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791812099; cv=none; b=n3Xll3P0vBqey+eYMU4+KloZMW9vhe6661G28mNbleklGd/brDERlgzNgkwF6lY7PIbK8d6b2udqEIKY+9tfcO+IzVKF25nZjk0eWQrbVyvYQ+7wl9lQB9r9gZij+Q/zDgnXwEKt+hBStICUBqSyBXj+FPJ1Faxpx/6lBchyoYk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791812099; c=relaxed/simple; bh=OhfL0GL8GJ86jahX5GdCFWMjyPBxJk0gmFh2OTmphns=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=aXweN2WKn+L8e6S0MD5dSL5XqafRdwTjdPiNE3/kaSbS07jS8VTdzKHJ3UGRjrUO1AKxnZK5KgjWMQZGzChB811V9Qi7v1X8WVSHyntmNOTiz4Rge1UbcXecb4LxwqB63yfkOAcyvMkBGo0eHXgTWgxyLou2SNs8pplZWjA5Hds= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ff8bMTf+; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Ff8bMTf+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3F8B11F0089B; Mon, 12 Oct 2026 13:34:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791812097; bh=w/DeowNBJKbFIs3vJCMnI0ObhW5niXOTwHtocWeV7dk=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=Ff8bMTf+7myqyUnSdtIx3d2O/3g8e2CsnV0ApHhxc8mJHmLFGYOtFne1SPzVtb20A H5Jfhi8h/9KcszNJNv6VIp+4oz3QP8E346tD2NZq8fChiwlgf7oF/z9nyGV10NNPiA 0Tf5e9YM5xqh4tBg3V1vYzGZ3qbF7/1R8ktMci3PKEfwBSPubC7449KPomT9VCWF+2 4DObNNzKzEwXQS51+RoivQyzqk8zd9g8QdvhrtboPrTav+4jytLZQAzz77ZiOPZeJw sXycZDc6F2sHuwcvq6tO9+ayJ6P1ZeQDABtWQZkr4oPPk/lsaAXmAkD1vGmUI7oMs6 pz3fRo3/FsAtw== From: =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= To: Stanislav Fomichev Cc: Magnus Karlsson , Maciej Fijalkowski , Stanislav Fomichev , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jonathan Corbet , Shuah Khan , Randy Dunlap , Alexander Duyck , kernel-team@meta.com, Andrew Lunn , Jesper Dangaard Brouer , Ilias Apalodimas , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Pavel Begunkov , Jens Axboe , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , netdev@vger.kernel.org, bpf@vger.kernel.org, io-uring@vger.kernel.org, "Mike Marciniszyn (Meta)" , Weiming Shi , Nikolay Aleksandrov , David Wei , Alexander Lobakin , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Mina Almasry Subject: Re: [RFC net-next 03/15] net: Add memory provider capabilities In-Reply-To: References: <20261002190018.696925-1-bjorn@kernel.org> <20261002190018.696925-4-bjorn@kernel.org> Date: Mon, 12 Oct 2026 15:34:54 +0200 Message-ID: <87h5irca9t.fsf@all.your.base.are.belong.to.us> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Stanislav Fomichev writes: > On 10/02, Bj=C3=B6rn T=C3=B6pel wrote: >> The current memory providers, devmem and io_uring zero-copy RX, give >> memory that the CPU cannot read. The core allows them only on queues >> with header-data split on, a zero header-split threshold, and no XDP >> program. AF_XDP needs a provider that the CPU can read and that >> works with XDP. >>=20 >> Add a capability field to the provider operations, with >> MP_CAP_READABLE as the first flag. Apply the header-split and XDP >> rules only to providers without it. A queue with an AF_XDP buffer >> pool still rejects other providers, but it accepts the provider made >> from that same pool. >>=20 >> Provider memory can become free while a queue is restarted, and no >> device event reports it. After a restart, and after a failed restart >> is rolled back, schedule the queue's NAPI if the queue has a >> provider, so the driver tries to refill. >>=20 >> Signed-off-by: Bj=C3=B6rn T=C3=B6pel >> --- >> Documentation/networking/netmem.rst | 7 ++- >> include/net/page_pool/memory_provider.h | 11 +++++ >> include/net/page_pool/types.h | 7 +-- >> net/core/dev.c | 4 +- >> net/core/netdev_rx_queue.c | 57 ++++++++++++++++++++----- >> net/ethtool/rings.c | 18 +++----- >> net/xdp/xsk_buff_pool.c | 3 +- >> 7 files changed, 78 insertions(+), 29 deletions(-) >>=20 >> diff --git a/Documentation/networking/netmem.rst b/Documentation/network= ing/netmem.rst >> index 217869d1108d..aacd185843ac 100644 >> --- a/Documentation/networking/netmem.rst >> +++ b/Documentation/networking/netmem.rst >> @@ -48,8 +48,11 @@ Driver RX Requirements >> - PP_FLAG_DMA_SYNC_DEV: netmem dma addr is not necessarily dma-synca= ble >> by the driver. The driver must delegate the dma syncing to the pag= e_pool, >> which knows when dma-syncing is (or is not) appropriate. >> - - PP_FLAG_ALLOW_UNREADABLE_NETMEM. The driver must specify this flag= iff >> - tcp-data-split is enabled. >> + - PP_FLAG_ALLOW_UNREADABLE_NETMEM. This opts the page pool into the = memory >> + provider configured on its RX queue. For a provider without >> + MP_CAP_READABLE, the driver must specify it only for a payload pool >> + with tcp-data-split enabled. A readable provider may also back a >> + regular or header pool. >>=20=20 >> 5. The driver must not assume the netmem is readable and/or backed by p= ages. >> The netmem returned by the page_pool may be unreadable, in which case >> diff --git a/include/net/page_pool/memory_provider.h b/include/net/page_= pool/memory_provider.h >> index 255ce4cfd975..d18ec079ffe2 100644 >> --- a/include/net/page_pool/memory_provider.h >> +++ b/include/net/page_pool/memory_provider.h >> @@ -9,6 +9,15 @@ struct netdev_rx_queue; >> struct netlink_ext_ack; >> struct sk_buff; >>=20=20 >> +/** >> + * enum mp_caps - memory provider capabilities >> + * @MP_CAP_READABLE: The CPU can access provider buffers. They may back >> + * header and regular page pools, and XDP programs may run on them. >> + */ >> +enum mp_caps { >> + MP_CAP_READABLE =3D BIT(0), >> +}; >> + >> struct memory_provider_ops { >> netmem_ref (*alloc_netmems)(struct page_pool *pool, gfp_t gfp); >> bool (*release_netmem)(struct page_pool *pool, netmem_ref netmem); >> @@ -17,11 +26,13 @@ struct memory_provider_ops { >> int (*nl_fill)(void *mp_priv, struct sk_buff *rsp, >> struct netdev_rx_queue *rxq); >> void (*uninstall)(void *mp_priv, struct netdev_rx_queue *rxq); >> + u32 caps; >> }; >>=20=20 >> bool net_mp_niov_set_dma_addr(struct net_iov *niov, dma_addr_t addr); >> void net_mp_niov_set_page_pool(struct page_pool *pool, struct net_iov *= niov); >> void net_mp_niov_clear_page_pool(struct net_iov *niov); >> +bool netif_mp_lacks_cap(struct net_device *dev, u32 cap); >>=20=20 >> int netif_mp_open_rxq(struct net_device *dev, unsigned int rxq_idx, >> const struct pp_memory_provider_params *p, >> diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types= .h >> index 03da138722f5..a96376613dda 100644 >> --- a/include/net/page_pool/types.h >> +++ b/include/net/page_pool/types.h >> @@ -22,9 +22,10 @@ >> */ >> #define PP_FLAG_SYSTEM_POOL BIT(2) /* Global system page_pool */ >>=20=20 >> -/* Allow unreadable (net_iov backed) netmem in this page_pool. Drivers = setting >> - * this must be able to support unreadable netmem, where netmem_address= () would >> - * return NULL. This flag should not be set for header page_pools. >> +/* Allow memory-provider (net_iov backed) netmem in this page_pool. Dri= vers >> + * setting this must honor the provider's capabilities. Unless the prov= ider has >> + * MP_CAP_READABLE, netmem_address() returns NULL, and the flag must no= t be set >> + * for a header page_pool. >> * >> * If the driver sets PP_FLAG_ALLOW_UNREADABLE_NETMEM, it should also s= et >> * page_pool_params.slow.queue_idx. >> diff --git a/net/core/dev.c b/net/core/dev.c >> index 5ac08da8b9d7..12b532c09a9c 100644 >> --- a/net/core/dev.c >> +++ b/net/core/dev.c >> @@ -10423,7 +10423,7 @@ int netif_xdp_propagate(struct net_device *dev, = struct netdev_bpf *bpf) >> return -EBUSY; >> } >>=20=20 >> - if (dev_get_min_mp_channel_count(dev)) { >> + if (netif_mp_lacks_cap(dev, MP_CAP_READABLE)) { >> NL_SET_ERR_MSG(bpf->extack, "unable to propagate XDP to device using = memory provider"); >> return -EBUSY; >> } >> @@ -10499,7 +10499,7 @@ static int dev_xdp_install(struct net_device *de= v, enum bpf_xdp_mode mode, >> return -EBUSY; >> } >>=20=20 >> - if (dev_get_min_mp_channel_count(dev)) { >> + if (netif_mp_lacks_cap(dev, MP_CAP_READABLE)) { >> NL_SET_ERR_MSG(extack, "unable to install XDP to device using memory = provider"); >> return -EBUSY; >> } >> diff --git a/net/core/netdev_rx_queue.c b/net/core/netdev_rx_queue.c >> index 00a7011eb4d5..610e31d1a717 100644 >> --- a/net/core/netdev_rx_queue.c >> +++ b/net/core/netdev_rx_queue.c >> @@ -82,8 +82,12 @@ __netif_get_rx_queue_lease(struct net_device **dev, u= nsigned int *rxq_idx, >> /* See also page_pool_is_unreadable() */ >> bool netif_rxq_has_unreadable_mp(struct net_device *dev, unsigned int r= xq_idx) >> { >> - if (rxq_idx < dev->real_num_rx_queues) >> - return __netif_get_rx_queue(dev, rxq_idx)->mp_params.mp_ops; >> + const struct memory_provider_ops *ops; >> + >> + if (rxq_idx < dev->real_num_rx_queues) { >> + ops =3D __netif_get_rx_queue(dev, rxq_idx)->mp_params.mp_ops; >> + return ops && !(ops->caps & MP_CAP_READABLE); >> + } >> return false; >> } >> EXPORT_SYMBOL(netif_rxq_has_unreadable_mp); >> @@ -95,6 +99,32 @@ bool netif_rxq_has_mp(struct net_device *dev, unsigne= d int rxq_idx) >> return false; >> } >>=20=20 >> +/* Return true if an installed memory provider lacks @cap. */ >> +bool netif_mp_lacks_cap(struct net_device *dev, u32 cap) >> +{ >> + const struct memory_provider_ops *ops; >> + int i; >> + >> + netdev_assert_locked_ops_compat(dev); >> + >> + for (i =3D dev->real_num_rx_queues - 1; i >=3D 0; i--) { >> + ops =3D dev->_rx[i].mp_params.mp_ops; >> + if (ops && (ops->caps & cap) !=3D cap) >> + return true; >> + } >> + >> + return false; >> +} >> + >> +/* Provider memory may become available while the queue is replaced, >> + * without a device event to report it. >> + */ >> +static void netdev_rx_queue_kick(struct netdev_rx_queue *rxq) >> +{ >> + if (rxq->mp_params.mp_ops && rxq->napi) >> + napi_schedule(rxq->napi); >> +} >> + >> static int netdev_rx_queue_reconfig(struct net_device *dev, >> unsigned int rxq_idx, >> struct netdev_queue_config *qcfg_old, > > [..] > >> @@ -142,6 +172,8 @@ static int netdev_rx_queue_reconfig(struct net_devic= e *dev, >> } >>=20=20 >> qops->ndo_queue_mem_free(dev, old_mem); >> + if (netif_running(dev)) >> + netdev_rx_queue_kick(rxq); >>=20=20 >> kvfree(old_mem); >> kvfree(new_mem); >> @@ -165,6 +197,11 @@ static int netdev_rx_queue_reconfig(struct net_devi= ce *dev, >>=20=20 >> err_free_new_queue_mem: >> qops->ndo_queue_mem_free(dev, new_mem); >> + /* Freeing the replacement can hand provider memory back to the old >> + * queue, which still runs unless the rollback failed. >> + */ >> + if (err !=3D -ENETDOWN && netif_running(dev)) >> + netdev_rx_queue_kick(rxq); >>=20=20 >> err_free_old_mem: >> kvfree(old_mem); > > These are separate fixes? Thanks for taking a look! The old pool can hold buffers the new pool needs. We need another refill after those buffers return. I'll split that from the capabilities patch. Bj=C3=B6rn