linux-kernel - Re: [PATCH] VMI: remove CONFIG_DEBUG_PAGE

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Message-ID: <468EA74D.7010706@vmware.com>
Date:	Fri, 06 Jul 2007 13:34:21 -0700
From:	Zachary Amsden <zach@...are.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Chris Wright <chrisw@...s-sol.org>, Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	virtualization@...ts.osdl.org,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	"Robert P. J. Day" <rpjday@...dspring.com>
Subject: Re: [PATCH] VMI: remove CONFIG_DEBUG_PAGE_TYPE and associated	bitrotted
 code

Jeremy Fitzhardinge wrote:
>>
>> I never merged the whole bit upstream because it added a field to 
>> struct page. 
>
> Hm, is that a big problem?  It would be OK for a debug config option, 
> wouldn't it?  Also, it doesn't seem particularly vmi-specific.  Could 
> it be made part of the pvops infrastructure?

I though about it, but it gets really ugly.  You need wrappers for all 
the MMU ops in pvops generic code, which means either another layer of 
wrappers or a bunch of CONFIG_DEBUG_PARAVIRT only things that are easy 
to break because they also depend on PAE vs. non-PAE.

It's doable, though, and might even be extensible to s390 for CMM page 
type debugging, as well as descriptor type tracking and enforcement of 
page isolation of GDTs.

Page state tracking could track -

PAGE_ZERO, PAGE_UNUSED, PAGE_STABLE, PAGE_VOLATILE, 
PAGE_POTENTIALLY_VOLATILE, PAGE_L1{2/3/4}, PAGE_LDT, PAGE_GDT,

actually, no this seems silly, since we'd just be duplicating bits for 
the page types, so the only debug benefit is ensuring the intersection 
of volatile and L{1/2/3/4} is nil, which is already trivially verifiable 
by inspection.

Zach
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