Re: [PATCH v2 02/12] x86: pgtable: Always use pte_free_kernel()

From: Dave Hansen <dave.hansen@intel.com>
To: Kevin Brodsky <kevin.brodsky@arm.com>, linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org, Albert Ou <aou@eecs.berkeley.edu>,
	Andreas Larsson <andreas@gaisler.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"David S. Miller" <davem@davemloft.net>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Madhavan Srinivasan <maddy@linux.ibm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Matthew Wilcox <willy@infradead.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	"Mike Rapoport (IBM)" <rppt@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Qi Zheng <zhengqi.arch@bytedance.com>,
	Ryan Roberts <ryan.roberts@arm.com>,
	Will Deacon <will@kernel.org>,
	Yang Shi <yang@os.amperecomputing.com>,
	linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-csky@vger.kernel.org, linux-m68k@lists.linux-m68k.org,
	linux-openrisc@vger.kernel.org, linux-riscv@lists.infradead.org,
	linux-s390@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	sparclinux@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH v2 02/12] x86: pgtable: Always use pte_free_kernel()
Date: Tue, 8 Apr 2025 08:22:47 -0700	[thread overview]
Message-ID: <409d2019-a409-4e97-a16f-6b345b0f5a38@intel.com> (raw)
In-Reply-To: <20250408095222.860601-3-kevin.brodsky@arm.com>

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@linux.intel.com>