linux-kernel - Re: [RFCv1 2/6] pagewalk: Add a page table walker for init

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Message-ID: <0deb55a5-8ed9-466d-8dca-1f4229ba9334@lucifer.local>
Date: Mon, 18 Nov 2024 10:32:37 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: Pasha Tatashin <pasha.tatashin@...een.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-doc@...r.kernel.org,
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Subject: Re: [RFCv1 2/6] pagewalk: Add a page table walker for init_mm page
 table

On Sun, Nov 17, 2024 at 10:49:06PM -0800, Christoph Hellwig wrote:
> On Sat, Nov 16, 2024 at 05:59:18PM +0000, Pasha Tatashin wrote:
> >  	} while (start = next, start < end);
> >  	return err;
> >  }
> > +EXPORT_SYMBOL_GPL(walk_page_range);
>
> Umm, no.  We really should not expose all these page table detail
> to modules.
>
> > +EXPORT_SYMBOL_GPL(walk_page_range_kernel);
>
> Even more so here.
>

Very much agree. You basically then have the ability for any (GPL) driver to
come in and modify page tables at will which is VERY MUCH not a good idea.

The rules around page table manipulation are very subtle and constantly
changing, this is not something for anything outside of mm to be fiddling with.

Again, I find it bizarre we're exporting mm internal implementation details to a
driver to do stuff with rather than adding functionality to mm.