From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH] net: don't use kvzalloc for DMA memory Date: Wed, 18 Apr 2018 09:51:25 -0700 Message-ID: <5f4e1286-b79f-0b9f-9a30-47d7654f3889__17754.527150146$1524073341$gmane$org@gmail.com> References: <3e65977e-53cd-bf09-bc4b-0ce40e9091fe@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Mikulas Patocka , Eric Dumazet Cc: "Michael S. Tsirkin" , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Eric Dumazet , Joby Poriyath , Ben Hutchings , "David S. Miller" List-Id: virtualization@lists.linuxfoundation.org On 04/18/2018 09:44 AM, Mikulas Patocka wrote: > > > On Wed, 18 Apr 2018, Eric Dumazet wrote: > >> >> >> On 04/18/2018 07:34 AM, Mikulas Patocka wrote: >>> The patch 74d332c13b21 changes alloc_netdev_mqs to use vzalloc if kzalloc >>> fails (later patches change it to kvzalloc). >>> >>> The problem with this is that if the vzalloc function is actually used, >>> virtio_net doesn't work (because it expects that the extra memory should >>> be accessible with DMA-API and memory allocated with vzalloc isn't). >>> >>> This patch changes it back to kzalloc and adds a warning if the allocated >>> size is too large (the allocation is unreliable in this case). >>> >>> Signed-off-by: Mikulas Patocka >>> Fixes: 74d332c13b21 ("net: extend net_device allocation to vmalloc()") >>> >>> --- >>> net/core/dev.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> Index: linux-2.6/net/core/dev.c >>> =================================================================== >>> --- linux-2.6.orig/net/core/dev.c 2018-04-16 21:08:36.000000000 +0200 >>> +++ linux-2.6/net/core/dev.c 2018-04-18 16:24:43.000000000 +0200 >>> @@ -8366,7 +8366,8 @@ struct net_device *alloc_netdev_mqs(int >>> /* ensure 32-byte alignment of whole construct */ >>> alloc_size += NETDEV_ALIGN - 1; >>> >>> - p = kvzalloc(alloc_size, GFP_KERNEL | __GFP_RETRY_MAYFAIL); >>> + WARN_ON(alloc_size > PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER); >>> + p = kzalloc(alloc_size, GFP_KERNEL | __GFP_RETRY_MAYFAIL); >>> if (!p) >>> return NULL; >>> >>> >> >> Since when a net_device needs to be in DMA zone ??? >> >> I would rather fix virtio_net, this looks very suspect to me. >> >> Each virtio_net should probably allocate the exact amount of DMA-memory it wants, >> instead of expecting core networking stack to have a huge chunk of DMA-memory for everything. > > The structure net_device is followed by arbitrary driver-specific data > (accessible with the function netdev_priv). And for virtio-net, these > driver-specific data must be in DMA memory. I get that, but how is the original xenvif problem will be solved ? Your patch would add a bug in some other driver(s) I suggest that virtio_net clearly identifies which part needs a specific allocation and does its itself, instead of abusing the netdev_priv storage. Ie use a pointer to a block of memory, allocated by virtio_net, for virtio_net.