On Mon, Jan 25, 2016 at 03:53:52PM +0000, Marc Zyngier wrote: > We already have hyp_alternate_select() to define a function pointer > that gets changed by a kernel feature or workaround. > > It would be useful to have a similar feature that resolves in a > direct value, without requiring a function call. For this purpose, > introduce hyp_alternate_value(), which returns one of two values > depending on the state of the alternative. > > Signed-off-by: Marc Zyngier <[email protected]> > --- > arch/arm64/kvm/hyp/hyp.h | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/arch/arm64/kvm/hyp/hyp.h b/arch/arm64/kvm/hyp/hyp.h > index 44eaff7..dc75fdb 100644 > --- a/arch/arm64/kvm/hyp/hyp.h > +++ b/arch/arm64/kvm/hyp/hyp.h > @@ -144,6 +144,17 @@ typeof(orig) * __hyp_text fname(void) > \ > return val; \ > } > > +#define hyp_alternate_value(fname, orig, alt, cond) \ > +typeof(orig) __hyp_text fname(void) \ > +{ \ > + typeof(alt) val = orig; \ > + asm volatile(ALTERNATIVE("nop \n", \ > + "mov %0, %1 \n", \ > + cond) \ > + : "+r" (val) : "r" ((typeof(orig))alt)); \ > + return val; \ > +} > + > void __vgic_v2_save_state(struct kvm_vcpu *vcpu); > void __vgic_v2_restore_state(struct kvm_vcpu *vcpu); > > -- > 2.1.4 > I'm really not convinced that this is more readable than simply defining a function where needed. Perhaps the thing that needs a definition is the "asm volatile(ALTERNATIVE(...))" part? I also don't see why any of this is specific to KVM or Hyp ?
-Christoffer
