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Tsirkin" To: Andrew Lunn Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Paolo Abeni , Jason Wang , Eugenio =?iso-8859-1?Q?P=E9rez?= , Xuan Zhuo , kvm@vger.kernel.org, virtualization@lists.linux.dev Subject: Re: [PATCH 3/3] vhost: use checked versions of VIRTIO_BIT Message-ID: <20251009085057-mutt-send-email-mst@kernel.org> References: <6629538adfd821c8626ab8b9def49c23781e6775.1760008798.git.mst@redhat.com> 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=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Oct 09, 2025 at 02:47:53PM +0200, Andrew Lunn wrote: > On Thu, Oct 09, 2025 at 07:24:16AM -0400, Michael S. Tsirkin wrote: > > This adds compile-time checked versions of VIRTIO_BIT that set bits in > > low and high qword, respectively. Will prevent confusion when people > > set bits in the wrong qword. > > > > Cc: "Paolo Abeni" > > Signed-off-by: Michael S. Tsirkin > > --- > > drivers/vhost/net.c | 4 ++-- > > include/linux/virtio_features.h | 9 +++++++++ > > 2 files changed, 11 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > index 43d51fb1f8ea..8b98e1a8baaa 100644 > > --- a/drivers/vhost/net.c > > +++ b/drivers/vhost/net.c > > @@ -76,8 +76,8 @@ static const u64 vhost_net_features[VIRTIO_FEATURES_QWORDS] = { > > (1ULL << VIRTIO_F_ACCESS_PLATFORM) | > > (1ULL << VIRTIO_F_RING_RESET) | > > (1ULL << VIRTIO_F_IN_ORDER), > > - VIRTIO_BIT(VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO) | > > - VIRTIO_BIT(VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO), > > + VIRTIO_BIT_HI(VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO) | > > + VIRTIO_BIT_HI(VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO), > > How any bits in vhost_net_features are currently in use? 68 > How likely is > it to go from 2x 64bit words to 3x 64 bit words? Maybe. > Rather than _LO, _HI, > would _1ST, _2ND be better leaving it open for _3RD? I can just open-code VIRTIO_BIT_QWORD(VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO, 1) > I would also be tempted to rename these macros to include _LO_ and > _HI_ in them. VIRTIO_BIT_HI(VIRTIO_LO_F_IN_ORDER) is more likely to be > spotted as wrong this way. Hmm but with my macros compiler will warn so why uglify then? > An alternative would be to convert to a linux bitmap, which is > arbitrary length so you just use bit number and leave the > implementation to map that to the correct offset in the underlying > data structure. > > Andrew Right but it's a bit more work as we then have to change all drivers. Not ruling this out, but this patchset is not aiming that high. -- MST