Re: [PATCH v3] hw/arm/virt: Avoid unexpected warning from Linux guest on host with Fujitsu CPUs

[Philippe Mathieu-Daudé]

On 12/6/24 14:48, Peter Maydell wrote:
> On Wed, 12 Jun 2024 at 13:33, Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
> > Hi Zhenyu,
> >
> > On 12/6/24 04:05, Zhenyu Zhang wrote:
> > > diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> > > index 3c93c0c0a6..3cefac6d43 100644
> > > --- a/hw/arm/virt.c
> > > +++ b/hw/arm/virt.c
> > > @@ -271,6 +271,17 @@ static void create_fdt(VirtMachineState *vms)
> > >        qemu_fdt_setprop_cell(fdt, "/", "#size-cells", 0x2);
> > >        qemu_fdt_setprop_string(fdt, "/", "model", "linux,dummy-virt");
> > >
> > > +    /*
> > > +     * For QEMU, all DMA is coherent. Advertising this in the root node
> > > +     * has two benefits:
> > > +     *
> > > +     * - It avoids potential bugs where we forget to mark a DMA
> > > +     *   capable device as being dma-coherent
> > > +     * - It avoids spurious warnings from the Linux kernel about
> > > +     *   devices which can't do DMA at all
> > > +     */
> > > +    qemu_fdt_setprop(fdt, "/", "dma-coherent", NULL, 0);
> >
> > OK, but why restrict that to the Aarch64 virt machine?
> > Shouldn't advertise this generically in create_device_tree()?
> > Or otherwise at least in the other virt machines?
>
> create_device_tree() creates an empty device tree, not one
> with stuff in it. It seems reasonable to me for this property
> on the root to be set in the same place we set other properties
> of the root node.

OK. Still the question about other virt machines remains
unanswered :)