linux-kernel - Re: [PATCH v2 02/12] x86: pgtable: Always use pte_free

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Message-ID: <409d2019-a409-4e97-a16f-6b345b0f5a38@intel.com>
Date: Tue, 8 Apr 2025 08:22:47 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Kevin Brodsky <kevin.brodsky@....com>, linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, Albert Ou <aou@...s.berkeley.edu>,
 Andreas Larsson <andreas@...sler.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Catalin Marinas <catalin.marinas@....com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 "David S. Miller" <davem@...emloft.net>,
 Geert Uytterhoeven <geert@...ux-m68k.org>,
 Linus Walleij <linus.walleij@...aro.org>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Mark Rutland <mark.rutland@....com>, Matthew Wilcox <willy@...radead.org>,
 Michael Ellerman <mpe@...erman.id.au>, "Mike Rapoport (IBM)"
 <rppt@...nel.org>, Palmer Dabbelt <palmer@...belt.com>,
 Paul Walmsley <paul.walmsley@...ive.com>,
 Peter Zijlstra <peterz@...radead.org>, Qi Zheng
 <zhengqi.arch@...edance.com>, Ryan Roberts <ryan.roberts@....com>,
 Will Deacon <will@...nel.org>, Yang Shi <yang@...amperecomputing.com>,
 linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-csky@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
 linux-openrisc@...r.kernel.org, linux-riscv@...ts.infradead.org,
 linux-s390@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v2 02/12] x86: pgtable: Always use pte_free_kernel()

On 4/8/25 02:52, Kevin Brodsky wrote:
> Page table pages are normally freed using the appropriate helper for
> the given page table level. On x86, pud_free_pmd_page() and
> pmd_free_pte_page() are an exception to the rule: they call
> free_page() directly.
> 
> Constructor/destructor calls are about to be introduced for kernel
> PTEs. To avoid missing dtor calls in those helpers, free the PTE
> pages using pte_free_kernel() instead of free_page().
> 
> While at it also use pmd_free() instead of calling pagetable_dtor()
> explicitly at the PMD level.

Looks sane and adding consistency is nice.

Are there any tests for folio_test_pgtable() at free_page() time? If we
had that, it would make it less likely that another free_page() user
could sneak in without calling the destructor.

Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>