On Mon, Feb 01, 2016 at 05:28:32PM +0000, Marc Zyngier wrote: > On 01/02/16 17:08, Ard Biesheuvel wrote: > > On 1 February 2016 at 17:20, Marc Zyngier <marc.zyngier@xxxxxxx> wrote: > >> On 01/02/16 15:36, Catalin Marinas wrote: > >>> On Mon, Feb 01, 2016 at 01:34:16PM +0000, Marc Zyngier wrote: > >>>> On 01/02/16 13:16, Christoffer Dall wrote: > >>>>> On Mon, Jan 25, 2016 at 03:53:40PM +0000, Marc Zyngier wrote: > >>>>>> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S > >>>>>> index 93e8d983..9e0683f 100644 > >>>>>> --- a/arch/arm64/kvm/hyp/hyp-entry.S > >>>>>> +++ b/arch/arm64/kvm/hyp/hyp-entry.S > >>>>>> @@ -38,6 +38,32 @@ > >>>>>> ldp x0, x1, [sp], #16 > >>>>>> .endm > >>>>>> > >>>>>> +.macro do_el2_call > >>>>>> + /* > >>>>>> + * Shuffle the parameters before calling the function > >>>>>> + * pointed to in x0. Assumes parameters in x[1,2,3]. > >>>>>> + */ > >>>>>> + stp lr, xzr, [sp, #-16]! > >>>>> > >>>>> remind me why this pair isn't just doing "str" instead of "stp" with the > >>>>> xzr ? > >>>> > >>>> Because SP has to be aligned on a 16 bytes boundary at all times. > >>> > >>> You could do something like: > >>> > >>> sub sp, sp, #16 > >>> str lr, [sp] > >>> > >> > >> Ah, fair enough. I'll fold that in. > >> > > > > Since we're micro-reviewing: what's wrong with > > > > str lr, [sp, #-16]! > > > > ? > > > > I suspect that on most micro-architectures, a register writeback is > going to be slower than doing the sub independently. > > I may be wrong, though. > For the record, I don't mind it the way it was in the original patch either, I was just curious about the store of xzr and had forgottten the stack alignment thing. -Christoffer -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
