linux-kernel - Re: [RFC v1 4/8] x86/init: add linker table support

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Date:	Thu, 21 Jan 2016 11:50:04 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
Cc:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Roger Pau Monné <roger.pau@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Andy Lutomirski <luto@...capital.net>, mcb30@...e.org,
	Juergen Gross <jgross@...e.com>,
	Jan Beulich <JBeulich@...e.com>, joro@...tes.org,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	andreyknvl@...gle.com, long.wanglong@...wei.com,
	qiuxishi@...wei.com, aryabinin@...tuozzo.com,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Valentin Rothberg <valentinrothberg@...il.com>,
	Peter Senna Tschudin <peter.senna@...il.com>,
	X86 ML <x86@...nel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v1 4/8] x86/init: add linker table support

On 01/21/16 11:46, Luis R. Rodriguez wrote:
> On Thu, Jan 21, 2016 at 11:25 AM, H. Peter Anvin <hpa@...or.com> wrote:
>>> And that's exactly what HVMlite does. Most of this shim layer is setting
>>> up boot_params, after which we jump to standard x86 boot path (i.e.
>>> startup_{32|64}). With hardware_subarch set to zero.
>>
>> Which is the way to do it as long as the early code can be the same.
> 
> To be clear, with the subarchand linker table suggested in my patch
> series, it should be possible to have the same exact entry point, the
> Xen PV setup code could run early in the order. For instance in the
> linker table we could use the reserved order levels 01-09 for PV
> hypervisor code:
> 
> +/* Init order levels, we can start at 01 but reserve 01-09 for now */
> +#define X86_INIT_ORDER_EARLY   10
> +#define X86_INIT_ORDER_NORMAL  30
> +#define X86_INIT_ORDER_LATE    50
> 
> So perhaps X86_INIT_ORDER_PV as 05 later.
> 
> The standard x86 init would just then be:
> 
> asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
> {
>         x86_init_fn_init_tables();
>         x86_init_fn_early_init();
> }
> 
> The PV init code would kick in early and could parse the
> boot_params.hdr.hardware_subarch_data pointer as it sees fit.
> 

Right... we already do that.

I don't even think you need to initialize any tables.  At least on i386,
we have to do this in assembly code.  However, it is just a simple table
walk.  :)

	-hpa