linux-kernel - Re: [PATCH V4 mm-hotfixes 2/3] mm: introduce and use {pgd,p4d}_populate

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Message-ID: <ef82f65a-f443-4341-9ae3-5d4e5cc9cee1@lucifer.local>
Date: Tue, 12 Aug 2025 17:08:29 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Harry Yoo <harry.yoo@...cle.com>
Cc: Dennis Zhou <dennis@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>, Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Tejun Heo <tj@...nel.org>, Uladzislau Rezki <urezki@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Christoph Lameter <cl@...two.org>,
        David Hildenbrand <david@...hat.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        "H. Peter Anvin" <hpa@...or.com>, kasan-dev@...glegroups.com,
        Mike Rapoport <rppt@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
        linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Suren Baghdasaryan <surenb@...gle.com>, Thomas Huth <thuth@...hat.com>,
        John Hubbard <jhubbard@...dia.com>, Michal Hocko <mhocko@...e.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>, linux-mm@...ck.org,
        "Kirill A. Shutemov" <kas@...nel.org>,
        Oscar Salvador <osalvador@...e.de>, Jane Chu <jane.chu@...cle.com>,
        Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Joerg Roedel <joro@...tes.org>, Alistair Popple <apopple@...dia.com>,
        Joao Martins <joao.m.martins@...cle.com>, linux-arch@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH V4 mm-hotfixes 2/3] mm: introduce and use
 {pgd,p4d}_populate_kernel()

On Tue, Aug 12, 2025 at 06:53:49PM +0900, Harry Yoo wrote:
> > I'd add that arm handles PGTBL_PMD_MODIFIED and therefore remains unaffected
> > just to be super clear.
>
> Will do:
>
> This change currently targets only x86_64, so only PGD and P4D level
> helpers are introduced. Currently, these helpers are no-ops since no
> architecture sets PGTBL_{PGD,P4D}_MODIFIED in ARCH_PAGE_TABLE_SYNC_MASK.
>
> In theory, PUD and PMD level helpers can be added later if needed by
> other architectures. For now, 32-bit architectures (x86-32 and arm)
> only handle PGTBL_PMD_MODIFIED, so p*d_populate_kernel() will never
> affect them unless we introduce a PMD level helper.

Sounds good!

Cheers, Lorenzo