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

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Message-ID: <CAKv+Gu9_KG7Zss3g1OMzcnRKQFhCcYtbSDEk-gwwgqPP-R6DOA@mail.gmail.com>
Date:	Mon, 1 Feb 2016 18:08:31 +0100
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	KVM devel mailing list <kvm@...r.kernel.org>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 06/21] arm64: KVM: VHE: Patch out use of HVC

On 1 February 2016 at 17:20, Marc Zyngier <marc.zyngier@....com> 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]!

?