On Sun, 4 Jan 2026, Helg wrote:

> Hi tech@
> 
> viogpu_wsmmap() returns a kva but instead should return a physical
> address via bus_dmamem_mmap(9). Without this, QEMU would only show a
> black screen when starting X11. On the Apple Hypervisor, the kernel
> would panic.
> 
> Also add calls to bus_dmamap_sync(9) before transferring the framebuffer
> to host memory. It was working for me without this, but this ensures
> that the host running on another CPU will see updates to the
> framebuffer.
> 
> Thanks to kettins@ for help with this.
> 
> ok?

with this, X seems to work on my ampera arm64 VM on kvm/qemu

ok sf@

> 
> 
> Index: viogpu.c
> ===================================================================
> RCS file: /cvs/src/sys/dev/pv/viogpu.c,v
> diff -u -p -r1.12 viogpu.c
> --- viogpu.c	16 Jan 2025 10:33:27 -0000	1.12
> +++ viogpu.c	4 Jan 2026 13:46:52 -0000
> @@ -539,6 +539,7 @@ int
>  viogpu_transfer_to_host_2d(struct viogpu_softc *sc, int resource_id,
>      uint32_t width, uint32_t height)
>  {
> +	struct virtio_softc *vsc = sc->sc_virtio;
>  	struct virtio_gpu_transfer_to_host_2d tth = { 0 };
>  	struct virtio_gpu_ctrl_hdr resp = { 0 };
>  
> @@ -547,6 +548,9 @@ viogpu_transfer_to_host_2d(struct viogpu
>  	tth.r.width = width;
>  	tth.r.height = height;
>  
> +	bus_dmamap_sync(vsc->sc_dmat, sc->sc_fb_dma_map, 0, sc->sc_fb_dma_size,
> +	    BUS_DMASYNC_PREWRITE);
> +
>  	viogpu_send_cmd(sc, &tth, sizeof(tth), &resp, sizeof(resp));
>  
>  	if (resp.type != VIRTIO_GPU_RESP_OK_NODATA) {
> @@ -555,6 +559,9 @@ viogpu_transfer_to_host_2d(struct viogpu
>  		return 1;
>  	}
>  
> +	bus_dmamap_sync(vsc->sc_dmat, sc->sc_fb_dma_map, 0, sc->sc_fb_dma_size,
> +	    BUS_DMASYNC_POSTWRITE);
> +
>  	return 0;
>  }
>  
> @@ -632,12 +639,15 @@ viogpu_wsmmap(void *v, off_t off, int pr
>  {
>  	struct rasops_info *ri = v;
>  	struct viogpu_softc *sc = ri->ri_hw;
> +	struct virtio_softc *vsc = sc->sc_virtio;
>  	size_t size = sc->sc_fb_dma_size;
> +	bus_dma_segment_t segs = sc->sc_fb_dma_seg;
>  
>  	if (off < 0 || off >= size)
>  		return -1;
>  
> -	return (((paddr_t)sc->sc_fb_dma_kva + off) | PMAP_NOCACHE);
> +	return bus_dmamem_mmap(vsc->sc_dmat, &segs, 1, off, prot,
> +	    BUS_DMA_WAITOK);
>  }
>  
>  int
> 
>