linux-kernel - Re: [PATCH v5 03/17] asm-generic: pgalloc: Provide generic p4d_{alloc

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Message-Id: <fd6e7ad9-9d57-40b6-a8f6-455ea3ab3d27@app.fastmail.com>
Date: Wed, 08 Jan 2025 12:01:31 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Qi Zheng" <zhengqi.arch@...edance.com>,
 "Peter Zijlstra" <peterz@...radead.org>,
 "Alexander Gordeev" <agordeev@...ux.ibm.com>,
 "Kevin Brodsky" <kevin.brodsky@....com>, "Alexandre Ghiti" <alex@...ti.fr>,
 "Andreas Larsson" <andreas@...sler.com>,
 "Palmer Dabbelt" <palmer@...belt.com>,
 "Thomas Gleixner" <tglx@...utronix.de>,
 "David Hildenbrand" <david@...hat.com>, "Jann Horn" <jannh@...gle.com>,
 "Hugh Dickins" <hughd@...gle.com>, "Yu Zhao" <yuzhao@...gle.com>,
 "Matthew Wilcox" <willy@...radead.org>,
 "Muchun Song" <muchun.song@...ux.dev>, vbabka@...nel.org,
 "Lorenzo Stoakes" <lorenzo.stoakes@...cle.com>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "David Rientjes" <rientjes@...gle.com>, vishal.moola@...il.com,
 "Will Deacon" <will@...nel.org>, aneesh.kumar@...nel.org,
 "Nicholas Piggin" <npiggin@...il.com>,
 "Dave Hansen" <dave.hansen@...ux.intel.com>,
 "Mike Rapoport" <rppt@...nel.org>, "Ryan Roberts" <ryan.roberts@....com>
Cc: linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
 linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
 linux-s390@...r.kernel.org, sparclinux@...r.kernel.org,
 linux-kernel@...r.kernel.org, x86@...nel.org,
 Linux-Arch <linux-arch@...r.kernel.org>,
 "linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
 linux-hexagon@...r.kernel.org, loongarch@...ts.linux.dev,
 linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
 "linux-openrisc@...r.kernel.org" <linux-openrisc@...r.kernel.org>,
 linux-sh@...r.kernel.org, linux-um@...ts.infradead.org
Subject: Re: [PATCH v5 03/17] asm-generic: pgalloc: Provide generic
 p4d_{alloc_one,free}

On Wed, Jan 8, 2025, at 07:57, Qi Zheng wrote:
> From: Kevin Brodsky <kevin.brodsky@....com>
>
> Four architectures currently implement 5-level pgtables: arm64,
> riscv, x86 and s390. The first three have essentially the same
> implementation for p4d_alloc_one() and p4d_free(), so we've got an
> opportunity to reduce duplication like at the lower levels.
>
> Provide a generic version of p4d_alloc_one() and p4d_free(), and
> make use of it on those architectures.
>
> Their implementation is the same as at PUD level, except that
> p4d_free() performs a runtime check by calling mm_p4d_folded().
> 5-level pgtables depend on a runtime-detected hardware feature on
> all supported architectures, so we might as well include this check
> in the generic implementation. No runtime check is required in
> p4d_alloc_one() as the top-level p4d_alloc() already does the
> required check.
>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> ---
>  arch/arm64/include/asm/pgalloc.h | 17 ------------
>  arch/riscv/include/asm/pgalloc.h | 23 ----------------
>  arch/x86/include/asm/pgalloc.h   | 18 -------------
>  include/asm-generic/pgalloc.h    | 45 ++++++++++++++++++++++++++++++++
>  4 files changed, 45 insertions(+), 58 deletions(-)

Acked-by: Arnd Bergmann <arnd@...db.de> # asm-generic