Re: [Qemu-devel] [PATCH qemu RFC 3/4] spapr: Advertise H_RTAS to the guest

[David Gibson <david@gibson.dropbear.id.au>]

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On Sat, Jul 20, 2019 at 11:28:49AM +1000, Alexey Kardashevskiy wrote:
> Since day 1 QEMU implemented RTAS as a custom hypercall wrapped into
> a small 20 bytes blob which guest would call to enter RTAS. Although
> it works fine, it is still a separate binary image which requires signing
> at no additional benefit.
> 
> This adds a flag into /chosen to tell a modified guest that if the flag
> is there, it can call H_RTAS directly and avoid calling into the RTAS
> blob.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  hw/ppc/spapr.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 81ad6a6f28de..b097a99951f1 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1230,6 +1230,9 @@ static void spapr_dt_chosen(SpaprMachineState *spapr, void *fdt)
>          _FDT(fdt_setprop_cell(fdt, chosen, "linux,pci-probe-only", 0));
>      }
>  
> +    /* We always implemented RTAS as hcall, tell guests to call it directly */
> +    _FDT(fdt_setprop_cell(fdt, chosen, "qemu,h_rtas", 1));

Rather than creating a new property for this we could use the
qemu,hypertas-functions property which is already used to advertise
some KVM specific hcalls.

>      spapr_dt_ov5_platform_support(spapr, fdt, chosen);
>  
>      g_free(stdout_path);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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