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: <e7d36cdc-9d12-4cd3-9480-d84422f9665e@redhat.com>
Date: Thu, 12 Jun 2025 18:00:54 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.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 12.06.25 17:59, Lorenzo Stoakes wrote:
> 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?

Same opinion, thanks!

-- 
Cheers,

David / dhildenb