linux-kernel - Re: [PATCH] x86 - Enhance DEBUG_RODATA support

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Date:	Tue, 11 Mar 2008 13:17:14 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	pageexec@...email.hu, Ingo Molnar <mingo@...e.hu>,
	Srinivasa DS <srinivasa@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, ananth@...ibm.com,
	Jim Keniston <jkenisto@...ibm.com>, srikar@...ux.vnet.ibm.com,
	SystemTAP <systemtap@...rces.redhat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH] x86 - Enhance DEBUG_RODATA support - alternatives

> First, that calling this text_poke implementation to modify text in a
> module won't fail. Is virt_to_page(addr) ok if addr is in a vmalloc'ed
> area ?

virt_to_page only works on direct mapping addresses, not vmalloc.
> 
> Second, that calling virt_to_page(addr + PAGE_SIZE) won't have
> undesirable side-effects if addr happens to be in the last page of an
> allocated range. It should be ok for the core kernel text, because it is
> followed by the kernel rodata, but I am not certain for modules.

On non vmemmap/none flatmem kernels it could fail yes. But vmalloc/module_alloc
is not guaranteed to be continuous so you cannot do that anyways.

-Andi
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