linux-kernel - Re: [PATCH v1 08/36] mm/hugetlb: check for unreasonable folio sizes when registering hstate

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Message-ID: <c4a0764e-e9eb-4571-a7ff-c26e8bd07401@lucifer.local>
Date: Fri, 29 Aug 2025 13:18:37 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brendan Jackman <jackmanb@...gle.com>,
        Christoph Lameter <cl@...two.org>, Dennis Zhou <dennis@...nel.org>,
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        John Hubbard <jhubbard@...dia.com>, kasan-dev@...glegroups.com,
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Subject: Re: [PATCH v1 08/36] mm/hugetlb: check for unreasonable folio sizes
 when registering hstate

On Fri, Aug 29, 2025 at 12:07:44PM +0200, David Hildenbrand wrote:
> On 28.08.25 16:45, Lorenzo Stoakes wrote:
> > On Thu, Aug 28, 2025 at 12:01:12AM +0200, David Hildenbrand wrote:
> > > Let's check that no hstate that corresponds to an unreasonable folio size
> > > is registered by an architecture. If we were to succeed registering, we
> > > could later try allocating an unsupported gigantic folio size.
> > >
> > > Further, let's add a BUILD_BUG_ON() for checking that HUGETLB_PAGE_ORDER
> > > is sane at build time. As HUGETLB_PAGE_ORDER is dynamic on powerpc, we have
> > > to use a BUILD_BUG_ON_INVALID() to make it compile.
> > >
> > > No existing kernel configuration should be able to trigger this check:
> > > either SPARSEMEM without SPARSEMEM_VMEMMAP cannot be configured or
> > > gigantic folios will not exceed a memory section (the case on sparse).
> >
> > I am guessing it's implicit that MAX_FOLIO_ORDER <= section size?
>
> Yes, we have a build-time bug that somewhere.

OK cool thanks!

>
> --
> Cheers
>
> David / dhildenb
>

Cheers, Lorenzo