Claudio Carvalho <cclau...@linux.ibm.com> writes: > diff --git a/arch/powerpc/kernel/ucall.S b/arch/powerpc/kernel/ucall.S > new file mode 100644 > index 000000000000..de9133e45d21 > --- /dev/null > +++ b/arch/powerpc/kernel/ucall.S > @@ -0,0 +1,20 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * Generic code to perform an ultravisor call. > + * > + * Copyright 2019, IBM Corporation. > + * > + */ > +#include <asm/ppc_asm.h> > +#include <asm/export.h> > + > +_GLOBAL(ucall_norets) > +EXPORT_SYMBOL_GPL(ucall_norets) > + mfcr r0 > + stw r0,8(r1) > + > + sc 2 /* Invoke the ultravisor */ > + > + lwz r0,8(r1) > + mtcrf 0xff,r0 > + blr /* Return r3 = status */
Paulus points that we shouldn't need to save CR here. Our caller will have already saved it if it needed to, and we don't use CR in this function so we don't need to save it. That's assuming the Ultravisor follows the hcall ABI in which CR2-4 are non-volatile (PAPR ยง 14.5.3). I know plpar_hcall_norets() does save CR, but it shouldn't need to, that seems to be historical. aka. no one knows why it does it but it always has. cheers
