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

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Date:   Fri, 2 Dec 2016 14:49:01 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     hpa@...or.com, Ingo Molnar <mingo@...nel.org>
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 12/02/2016 12:52 PM, hpa@...or.com wrote:
> 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.


I can still give it a try but I'd rather not tie it to this (Xen PVH)
patch series. Which would leave me with two options: either keep what
this patch does, leaving it as assembly (requires your ack), or have Xen
code build the pages on its own.

-boris