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[80.230.79.166]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43970d3ff1csm31882149f8f.20.2026.02.25.01.24.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Feb 2026 01:24:17 -0800 (PST) Date: Wed, 25 Feb 2026 04:24:14 -0500 From: "Michael S. Tsirkin" To: Xuan Zhuo Cc: Srujana Challa , pabeni@redhat.com, jasowang@redhat.com, eperezma@redhat.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, ndabilpuram@marvell.com, kshankar@marvell.com, netdev@vger.kernel.org, virtualization@lists.linux.dev Subject: Re: [PATCH net-next,2/2] virtio_net: replace RSS key size max check with BUILD_BUG_ON Message-ID: <20260225042302-mutt-send-email-mst@kernel.org> References: <20260224065850.962826-1-schalla@marvell.com> <20260224065850.962826-2-schalla@marvell.com> <1772010702.3747633-2-xuanzhuo@linux.alibaba.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1772010702.3747633-2-xuanzhuo@linux.alibaba.com> On Wed, Feb 25, 2026 at 05:11:42PM +0800, Xuan Zhuo wrote: > On Tue, 24 Feb 2026 12:28:50 +0530, Srujana Challa wrote: > > Since NETDEV_RSS_KEY_LEN was increased to 256 in net-next, use > > BUILD_BUG_ON to enforce the limit at compile time and remove the > > redundant runtime max check. > > > > Signed-off-by: Srujana Challa > > --- > > drivers/net/virtio_net.c | 8 +------- > > 1 file changed, 1 insertion(+), 7 deletions(-) > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > index eeefe8abc122..768ad5523dfa 100644 > > --- a/drivers/net/virtio_net.c > > +++ b/drivers/net/virtio_net.c > > @@ -6639,13 +6639,7 @@ static int virtnet_validate(struct virtio_device *vdev) > > __virtio_clear_bit(vdev, VIRTIO_NET_F_RSS); > > __virtio_clear_bit(vdev, VIRTIO_NET_F_HASH_REPORT); > > } > > - if (key_sz > NETDEV_RSS_KEY_LEN) { > > - dev_warn(&vdev->dev, > > - "rss_max_key_size=%u exceeds driver limit %u, disabling RSS\n", > > - key_sz, NETDEV_RSS_KEY_LEN); > > - __virtio_clear_bit(vdev, VIRTIO_NET_F_RSS); > > - __virtio_clear_bit(vdev, VIRTIO_NET_F_HASH_REPORT); > > - } > > + BUILD_BUG_ON(type_max(key_sz) >= NETDEV_RSS_KEY_LEN); > > Do we really need this check? > > If I understand correctly, the intention is to cap key_sz at 256. However, since > key_sz is of type u8, its maximum value is inherently 255, making this check > redundant. This is not only limited by this kernel code, the virtio-net spec > defines this. That's why it's BUILD_BUG_ON. It checks it has the right type. We never *need* BUILD_BUG_ON by definition, what this does is document the assumption. > Moreover, if NETDEV_RSS_KEY_LEN is ever reduced to a value smaller than 256 in > the future, this check would no longer enforce the intended limit correctly. then it would fail build. > > Moreover, you should add a cover letter. > > Thanks. > > > > > > > } > > > > return 0; > > -- > > 2.25.1 > >