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

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Date:   Fri, 02 Dec 2016 09:52:44 -0800
From:   hpa@...or.com
To:     Ingo Molnar <mingo@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, david.vrabel@...rix.com,
        JGross@...e.com, roger.pau@...rix.com,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        x86@...nel.org, Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH 2/8] x86/head: Refactor 32-bit pgtable setup

On December 2, 2016 8:08:55 AM PST, Ingo Molnar <mingo@...nel.org> wrote:
>
>* Boris Ostrovsky <boris.ostrovsky@...cle.com> wrote:
>
>> On 12/02/2016 04:45 AM, Ingo Molnar wrote:
>> > * Boris Ostrovsky <boris.ostrovsky@...cle.com> wrote:
>> >
>> >> On 10/31/2016 08:33 AM, Boris Ostrovsky wrote:
>> >>>
>> >>> On 10/14/2016 02:05 PM, Boris Ostrovsky 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.
>> >>>
>> >>> Ping to x86 maintainers.
>> >> Pinging again.
>> >>
>> >> I will be re-sending this series at some point (it has been
>delayed by
>> >> some hypervisor changes that will be needed) but I'd like to hear
>from
>> >> x86 maintainers whether this will be acceptable before I post this
>again.
>> > Could this be done in C?
>> 
>> I suppose it could be, I haven't thought about it.
>> 
>> The goal here was to simply make existing startup code available to
>others (Xen 
>> guest) without changes. Are you suggesting to build page tables in C
>for the Xen 
>> guest only or to make startup_32 call new C code as well?
>
>My suggestion would be to transform the factored out assembly code to
>C.
>
>Thanks,
>
>	Ingo

It is tricky to do so safely, because at this stage almost nothing of the C execution environment has been set up.
-- 
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