linux-kernel - Re: [PATCH v2 06/21] arm64: KVM: VHE: Patch out use of HVC

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Date:	Mon, 1 Feb 2016 15:36:35 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Christoffer Dall <christoffer.dall@...aro.org>,
	kvm@...r.kernel.org, Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 06/21] arm64: KVM: VHE: Patch out use of HVC

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]

-- 
Catalin