linux-kernel - Re: [PATCH v4 0/7] mm/mprotect: Fix dax puds

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Message-Id: <20240807141703.d641001ee14177ccf80a31d8@linux-foundation.org>
Date: Wed, 7 Aug 2024 14:17:03 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Peter Xu <peterx@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, "Aneesh Kumar K . V"
 <aneesh.kumar@...ux.ibm.com>, Michael Ellerman <mpe@...erman.id.au>, Oscar
 Salvador <osalvador@...e.de>, Dan Williams <dan.j.williams@...el.com>,
 James Houghton <jthoughton@...gle.com>, Matthew Wilcox
 <willy@...radead.org>, Nicholas Piggin <npiggin@...il.com>, Rik van Riel
 <riel@...riel.com>, Dave Jiang <dave.jiang@...el.com>, x86@...nel.org, Ingo
 Molnar <mingo@...hat.com>, Rick P Edgecombe <rick.p.edgecombe@...el.com>,
 "Kirill A . Shutemov" <kirill@...temov.name>,
 linuxppc-dev@...ts.ozlabs.org, Mel Gorman <mgorman@...hsingularity.net>,
 Hugh Dickins <hughd@...gle.com>, Borislav Petkov <bp@...en8.de>, David
 Hildenbrand <david@...hat.com>, Thomas Gleixner <tglx@...utronix.de>,
 Vlastimil Babka <vbabka@...e.cz>, Dave Hansen
 <dave.hansen@...ux.intel.com>, Christophe Leroy
 <christophe.leroy@...roup.eu>, Huang Ying <ying.huang@...el.com>
Subject: Re: [PATCH v4 0/7] mm/mprotect: Fix dax puds

On Wed,  7 Aug 2024 15:48:04 -0400 Peter Xu <peterx@...hat.com> wrote:

> 
> Dax supports pud pages for a while, but mprotect on puds was missing since
> the start.  This series tries to fix that by providing pud handling in
> mprotect().  The goal is to add more types of pud mappings like hugetlb or
> pfnmaps.  This series paves way for it by fixing known pud entries.
> 
> Considering nobody reported this until when I looked at those other types
> of pud mappings, I am thinking maybe it doesn't need to be a fix for stable
> and this may not need to be backported.  I would guess whoever cares about
> mprotect() won't care 1G dax puds yet, vice versa.  I hope fixing that in
> new kernels would be fine, but I'm open to suggestions.

Yes, I'm not sure this is a "fix" at all.  We're implementing something
which previously wasn't there.  Perhaps the entire series should be
called "mm: implement mprotect() for DAX PUDs"?