linux-kernel - Re: [PATCH 2/8] x86/head: Refactor 32-bit pgtable setup

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Message-ID: <CFB7B4F4-CE78-4129-BB4E-A599384E7A42@zytor.com>
Date:   Fri, 14 Oct 2016 12:04:42 -0700
From:   hpa@...or.com
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        david.vrabel@...rix.com, JGross@...e.com
CC:     roger.pau@...rix.com, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH 2/8] x86/head: Refactor 32-bit pgtable setup

On October 14, 2016 11:44:18 AM PDT, Boris Ostrovsky <boris.ostrovsky@...cle.com> wrote:
>On 10/14/2016 02:31 PM, hpa@...or.com wrote:
>> On October 14, 2016 11:05:12 AM PDT, Boris Ostrovsky
><boris.ostrovsky@...cle.com> wrote:
>>> From: Matt Fleming <matt@...eblueprint.co.uk>
>>>
>>> The new Xen PVH entry point requires page tables to be setup by the
>>> kernel since it is entered with paging disabled.
>>>
>>> Pull the common code out of head_32.S and into pgtable_32.S so that
>>> setup_pgtable_32 can be invoked from both the new Xen entry point
>and
>>> the existing startup_32 code.
>>>
>> And why does it need a separate entry point as opposed to the plain
>one?
>
>One reason is that we need to prepare boot_params before jumping to
>startup_{32|64}.
>
>When the guest is loaded (always in 32-bit mode) the only thing we have
>is a pointer to Xen-specific datastructure. The early PVH code will
>prepare zeropage based on that structure and then jump to regular
>startup_*() code.
>
>-boris

And why not just resume execution at start_32 then?
-- 
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