On 1/28/26 10:03 AM, Alexander Graf wrote: > On 28.01.26 09:47, Johannes Thumshirn wrote: >> On 1/27/26 5:30 PM, Alexander Graf wrote: >>> This patches the split vring format, but does not touch the packed one. >>> What happens if you run the same test with the packed format? You can do >>> so by passing "packed=on" as argument to your -device parameter. >> This opened up a whole new can of worms... :( > > That's what I expected :). > > How do other DMA based devices handle this? Is the real problem that > virtio by default does not use the DMA API and so it confuses generic > KCSAN logic that would otherwise track DMA regions as "can be modified > by DMA at any time"? > > If that is the case, maybe what we really want is to force enable use of > the DMA API when KCSAN is active. Does something like the (whitespace > broken) patch below work? > > Alex > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index ddab68959671..b1dd790ce622 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -284,6 +284,13 @@ static bool vring_use_map_api(const struct > virtio_device *vdev) > if (xen_domain()) > return true; > > + /* > + * KCSAN needs to track who can modify memory. DMA API gets > + * us that, so always use it. > + */ > + if (IS_ENABLED(CONFIG_KCSAN)) > + return true; > + > return false; > }
Unfortunately this doesn't get us any further (I'd love though, it looks way cleaner!) I still see the KCSAN messages even on boot.
