linux-kernel - Re: [PATCH v2 1/3] mm/huge_memory: don't ignore queried cachemode in vmf_insert_pfn

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Message-ID: <dfab0736-4a62-4e2f-889e-3d6fdb4564be@lucifer.local>
Date: Thu, 12 Jun 2025 16:59:19 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, nvdimm@...ts.linux.dev,
        linux-cxl@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
        Alistair Popple <apopple@...dia.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
        Dev Jain <dev.jain@....com>, Dan Williams <dan.j.williams@...el.com>,
        Oscar Salvador <osalvador@...e.de>, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/3] mm/huge_memory: don't ignore queried cachemode in
 vmf_insert_pfn_pud()

On Thu, Jun 12, 2025 at 05:36:35PM +0200, David Hildenbrand wrote:
> On 12.06.25 17:28, Lorenzo Stoakes wrote:
> > On Wed, Jun 11, 2025 at 02:06:52PM +0200, David Hildenbrand wrote:
> > > We setup the cache mode but ... don't forward the updated pgprot to
> > > insert_pfn_pud().
> > >
> > > Only a problem on x86-64 PAT when mapping PFNs using PUDs that
> > > require a special cachemode.
> > >
> > > Fix it by using the proper pgprot where the cachemode was setup.
> > >
> > > Identified by code inspection.
> > >
> > > Fixes: 7b806d229ef1 ("mm: remove vmf_insert_pfn_xxx_prot() for huge page-table entries")

Ha! I don't even remember doing that patch... hm did I introduce this -ignoring
cache- thing? Sorry! :P

> > > Cc: <stable@...r.kernel.org>
> > > Signed-off-by: David Hildenbrand <david@...hat.com>
> >
> > Nice catch!
> >
> > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>
> Thanks! What's your opinion on stable? Really hard to judge the impact ...

I think it makes sense? This is currently incorrect so let's do the right thing
and backport.

I think as per Dan it's probably difficult to picture this causing a problem,
but on principle I think this is correct, and I don't see any harm in
backporting?

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