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 <marc.zyngier@xxxxxxx>
> ---
> 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
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