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[213.179.129.39]) by smtp.gmail.com with ESMTPSA id gh31-20020a1709073c1f00b008b1797b77b2sm7422313ejc.221.2023.02.21.23.59.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Feb 2023 23:59:23 -0800 (PST) Date: Wed, 22 Feb 2023 08:59:22 +0100 From: Jiri Pirko To: "Michael S. Tsirkin" Cc: netdev@vger.kernel.org, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, edumazet@google.com, jasowang@redhat.com, virtualization@lists.linux-foundation.org, alvaro.karsz@solid-run.com, vmireyno@marvell.com, parav@nvidia.com Subject: Re: [patch net-next v2] net: virtio_net: implement exact header length guest feature Message-ID: References: <20230221144741.316477-1-jiri@resnulli.us> <20230221121543-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230221121543-mutt-send-email-mst@kernel.org> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Tue, Feb 21, 2023 at 06:21:16PM CET, mst@redhat.com wrote: >On Tue, Feb 21, 2023 at 03:47:41PM +0100, Jiri Pirko wrote: >> From: Jiri Pirko >> >> Virtio spec introduced a feature VIRTIO_NET_F_GUEST_HDRLEN which when >> set implicates that the driver provides the exact size of the header. > >OK but I feel this is not the important point. The important points are: >- this bit means device needs this info >- driver also has to set this bit >For example one might replace above with: > > Virtio spec introduced a feature VIRTIO_NET_F_GUEST_HDRLEN which when > which when set implicates that device benefits from knowing the exact > size of the header. For compatiblity, to signal to the device that the header > is reliable driver also needs to set this feature. > Without this feature set by driver, device has to figure > out the header size itself. > >and the below is ok. > >> Quoting the original virtio spec: >> "hdr_len is a hint to the device as to how much of the header needs to >> be kept to copy into each packet" >> >> "a hint" might not be clear for the reader what does it mean, if it is >> "maybe like that" of "exactly like that". This feature just makes it >> crystal clear and let the device count on the hdr_len being filled up >> by the exact length of header. >> >> Also note the spec already has following note about hdr_len: >> "Due to various bugs in implementations, this field is not useful >> as a guarantee of the transport header size." >> >> Without this feature the device needs to parse the header in core >> data path handling. Accurate information helps the device to eliminate >> such header parsing and directly use the hardware accelerators >> for GSO operation. >> >> virtio_net_hdr_from_skb() fills up hdr_len to skb_headlen(skb). >> The driver already complies to fill the correct value. Introduce the >> feature and advertise it. >> >> Note that virtio spec also includes following note for device >> implementation: >> "Caution should be taken by the implementation so as to prevent >> a malicious driver from attacking the device by setting >> an incorrect hdr_len." >> >> There is a plan to support this feature in our emulated device. >> A device of SolidRun offers this feature bit. They claim this feature >> will save the device a few cycles for every GSO packet. >> >> Signed-off-by: Jiri Pirko > >I'm fine with patch itself. with commit log tweak: > >Acked-by: Michael S. Tsirkin Okay. Will do. I will put link to the spec as well Thanks! > > >> --- >> v1->v2: >> - extended patch description >> --- >> drivers/net/virtio_net.c | 6 ++++-- >> include/uapi/linux/virtio_net.h | 1 + >> 2 files changed, 5 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >> index fb5e68ed3ec2..e85b03988733 100644 >> --- a/drivers/net/virtio_net.c >> +++ b/drivers/net/virtio_net.c >> @@ -62,7 +62,8 @@ static const unsigned long guest_offloads[] = { >> VIRTIO_NET_F_GUEST_UFO, >> VIRTIO_NET_F_GUEST_CSUM, >> VIRTIO_NET_F_GUEST_USO4, >> - VIRTIO_NET_F_GUEST_USO6 >> + VIRTIO_NET_F_GUEST_USO6, >> + VIRTIO_NET_F_GUEST_HDRLEN >> }; >> >> #define GUEST_OFFLOAD_GRO_HW_MASK ((1ULL << VIRTIO_NET_F_GUEST_TSO4) | \ >> @@ -4213,7 +4214,8 @@ static struct virtio_device_id id_table[] = { >> VIRTIO_NET_F_CTRL_MAC_ADDR, \ >> VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \ >> VIRTIO_NET_F_SPEED_DUPLEX, VIRTIO_NET_F_STANDBY, \ >> - VIRTIO_NET_F_RSS, VIRTIO_NET_F_HASH_REPORT, VIRTIO_NET_F_NOTF_COAL >> + VIRTIO_NET_F_RSS, VIRTIO_NET_F_HASH_REPORT, VIRTIO_NET_F_NOTF_COAL, \ >> + VIRTIO_NET_F_GUEST_HDRLEN >> >> static unsigned int features[] = { >> VIRTNET_FEATURES, >> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h >> index b4062bed186a..12c1c9699935 100644 >> --- a/include/uapi/linux/virtio_net.h >> +++ b/include/uapi/linux/virtio_net.h >> @@ -61,6 +61,7 @@ >> #define VIRTIO_NET_F_GUEST_USO6 55 /* Guest can handle USOv6 in. */ >> #define VIRTIO_NET_F_HOST_USO 56 /* Host can handle USO in. */ >> #define VIRTIO_NET_F_HASH_REPORT 57 /* Supports hash report */ >> +#define VIRTIO_NET_F_GUEST_HDRLEN 59 /* Guest provides the exact hdr_len value. */ >> #define VIRTIO_NET_F_RSS 60 /* Supports RSS RX steering */ >> #define VIRTIO_NET_F_RSC_EXT 61 /* extended coalescing info */ >> #define VIRTIO_NET_F_STANDBY 62 /* Act as standby for another device >> -- >> 2.39.0 >