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

[Alexey Kardashevskiy <aik@ozlabs.ru>]

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));
+
     spapr_dt_ov5_platform_support(spapr, fdt, chosen);
 
     g_free(stdout_path);
-- 
2.17.1