linux-kernel - Re: [PATCH] x86/mm/init: respect memblock reserved regions when destroying mappings

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Message-ID: <4D506A85.9030802@goop.org>
Date:	Mon, 07 Feb 2011 13:56:21 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jan Beulich <JBeulich@...ell.com>
Subject: Re: [PATCH] x86/mm/init: respect memblock reserved regions when destroying
 mappings

On 02/07/2011 11:00 AM, Yinghai Lu wrote:
> On 02/07/2011 10:58 AM, Stefano Stabellini wrote:
>> On Mon, 7 Feb 2011, Yinghai Lu wrote:
>>> On 02/07/2011 08:50 AM, Stefano Stabellini wrote:
>>>> On Sun, 6 Feb 2011, Yinghai Lu wrote:
>>>>> On 02/05/2011 11:30 PM, H. Peter Anvin wrote:
>>>>>> On 02/05/2011 11:02 PM, Yinghai Lu wrote:
>>>>>>> why not just move calling cleanup_highmap down?
>>>>>>>
>>>>>>> something like attached patch.
>>>>>> This patch looks very clean and looks on the surface of it like it is
>>>>>> removing some ugly ad hoc code, but (as always) it needs a description
>>>>>> about the problem it solves and why it is correct.
>>>>> Sure.
>>>>>
>>>>>
>>>>> Jeremy and xen guys, can you please check if it works well with xen ?
>>>>>
>>>> Actually this patch makes things worse on xen, because before
>>>> cleanup_highmap() wasn't called at all on xen (on purpose) and now it
>>>> is, fully destroying all the mappings we have at _end.
>>>>
>>>> Can we add a check on memblock reserved regions in cleanup_highmap()?
>>>> Otherwise could we avoid calling cleanup_highmap() at all on xen?
>>> why DO xen need over-mapped kernel initial mapping?
>>>
>>> what is in that range after _end to 512M?
>> The mfn list that is the list of machine frame numbers assigned to this
>> domain; it is used across the kernel to convert pfns into mfns.
>> It passed to us at that address by the domain builder.
> is it possible for you to pass physical address, and then map it in kernel?

That is possible in principle, but very difficult in practice.

What's wrong with honouring reserved memory ranges under all circumstances?

    J
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