linux-kernel - Re: [RFC PATCH V2] ARM: EXYNOS: Fix hotplug when CPUs boot in HYP mode

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Date:	Wed, 8 May 2013 17:53:04 +0530
From:	Giridhar Maruthy <giridhar.maruthy@...aro.org>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	"kgene.kim@...sung.com" <kgene.kim@...sung.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	Christoffer Dall <cdall@...columbia.edu>
Subject: Re: [RFC PATCH V2] ARM: EXYNOS: Fix hotplug when CPUs boot in HYP mode

On 7 May 2013 14:25, Marc Zyngier <marc.zyngier@....com> wrote:
> On 07/05/13 06:54, Giridhar Maruthy wrote:
>> This patch is a modification from the Christoffer Dall's u-boot
>> patch. This is required to put the secondary processors in hyp
>> mode during cpu hotplug when u-boot is no longer alive.
>>
>> Marc Zyngier suggested this logic to go into firmware or, u-boot
>> putting a trampoline code into a page /memreserve/d by DT. But
>> this seemed to have a problem. Once the cpu is hotplugged in
>> runtime, the control is in ROM code and waits for event.
>> Kernel provides a return address in kernel to which the processor
>> jumps once it gets an event. If the control branches to the
>> trampoline code here, this trampoline code has no kernel return
>> address.
>>
>> Someone with better logic or better placement of this logic
>> elsewhere is welcome.
>
> What prevents you from writing the kernel address in the memreserved
> page? Some obvious location, like the last word of the page? You only
> have to do it once (from the boot CPU, for example).
>
> Or did I miss something else?

Thanks Marc, I think I understand now.

I guess I also need to put the primary cpu boot mode into a temporary location.

-Giridhar
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