linux-kernel - Re: [RFC PATCH 1/4] drivers/iommu: Add page_ext for IOMMU_DEBUG

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Message-ID: <aQIi3-l7juuwLZzs@google.com>
Date: Wed, 29 Oct 2025 14:21:19 +0000
From: Mostafa Saleh <smostafa@...gle.com>
To: Jörg Rödel <joro@...tes.org>
Cc: linux-mm@...ck.org, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, corbet@....net, will@...nel.org,
	robin.murphy@....com, akpm@...ux-foundation.org, vbabka@...e.cz,
	surenb@...gle.com, mhocko@...e.com, jackmanb@...gle.com,
	hannes@...xchg.org, ziy@...dia.com, david@...hat.com,
	lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com,
	rppt@...nel.org
Subject: Re: [RFC PATCH 1/4] drivers/iommu: Add page_ext for
 IOMMU_DEBUG_PAGEALLOC

On Mon, Oct 27, 2025 at 12:42:09PM +0100, Jörg Rödel wrote:
> On Fri, Oct 03, 2025 at 05:32:26PM +0000, Mostafa Saleh wrote:
> > +config IOMMU_DEBUG_PAGEALLOC
> > +	bool "Debug page memory allocations against IOMMU"
> > +	depends on DEBUG_PAGEALLOC && IOMMU_API && PAGE_EXTENSION
> > +	help
> > +		This config checks when a page is freed by the kernel
> > +		it's not mapped in any IOMMU domain. It can help with
> > +		debugging use-after-free from driver doing DMA.
> > +		This santaizer can have false-negative cases where some
> > +		problems won't be detected.
> > +		Expect overhead when enabling this + enabling the kernel
> > +		command line iommu.debug_pagealloc.
> > +
> > +		If unsure, say N here.
> 
> Expected indentation here is <tab><space><space> and not <tab><tab>.

My bad, I will fix it in v2.

> 
> > --- /dev/null
> > +++ b/drivers/iommu/iommu-debug.c
> 
> Is there a plan for this file to contain more than page-alloc debugging? If
> not, it should get a more specific name, like iommu-debug-pagealloc.c or
> similar.


I have no solid plans for other features, but I was hoping to build on top
of that in the future, but for now we can make it “iommu-debug-pagealloc.c”

Thanks,
Mostafa

>