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

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Date:   Fri, 14 Oct 2016 14:44:18 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     hpa@...or.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 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