linux-kernel - Re: [PATCH v7u1 10/31] x86, 64bit: Don't set max_pfn

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Date:	Tue, 15 Jan 2013 08:37:46 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>, Jan Kiszka <jan.kiszka@....de>,
	Jason Wessel <jason.wessel@...driver.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH v7u1 10/31] x86, 64bit: Don't set max_pfn_mapped wrong
 value early on native path

On Tue, Jan 15, 2013 at 5:48 AM, Stefano Stabellini
<stefano.stabellini@...citrix.com> wrote:

>
> If you are going to put a comment like that in the code, could you
> please at least add some useful details, rather than a generic
> "somehow"? It doesn't seem very helpful to me or to any other hackers
> looking at the code.
>
> The issue is even described as a comment in the code at the beginning of
> arch/x86/xen/mmu.c:xen_setup_kernel_pagetable:
>
> /* max_pfn_mapped is the last pfn mapped in the initial memory
>  * mappings. Considering that on Xen after the kernel mappings we
>  * have the mappings of some pages that don't exist in pfn space, we
>  * set max_pfn_mapped to the last real pfn mapped. */
>
> Now if max_pfn_mapped is supposed to represent the last pfn mapped in
> the initial memory mapping, then I think that the way Xen uses
> max_pfn_mapped is actually correct.

change the comments to:

+       /*
+        * Native path, max_pfn_mapped is not set yet.
+        * Xen has valid max_pfn_mapped set in
+        *      arch/x86/xen/mmu.c:xen_setup_kernel_pagetable().
+        */


Thanks

Yinghai
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