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Mon, 06 Jan 2025 02:56:13 -0800 (PST) Message-ID: Date: Mon, 6 Jan 2025 18:55:58 +0800 Precedence: bulk X-Mailing-List: linux-m68k@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 07/15] mm: pgtable: introduce pagetable_dtor() Content-Language: en-US To: Alexander Gordeev Cc: peterz@infradead.org, kevin.brodsky@arm.com, palmer@dabbelt.com, tglx@linutronix.de, david@redhat.com, jannh@google.com, hughd@google.com, yuzhao@google.com, willy@infradead.org, muchun.song@linux.dev, vbabka@kernel.org, lorenzo.stoakes@oracle.com, akpm@linux-foundation.org, rientjes@google.com, vishal.moola@gmail.com, arnd@arndb.de, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, dave.hansen@linux.intel.com, rppt@kernel.org, ryan.roberts@arm.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, loongarch@lists.linux.dev, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-openrisc@vger.kernel.org, linux-sh@vger.kernel.org, linux-um@lists.infradead.org References: <8ada95453180c71b7fca92b9a9f11fa0f92d45a6.1735549103.git.zhengqi.arch@bytedance.com> From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2025/1/6 18:34, Alexander Gordeev wrote: > On Mon, Dec 30, 2024 at 05:07:42PM +0800, Qi Zheng wrote: >> The pagetable_p*_dtor() are exactly the same except for the handling of >> ptlock. If we make ptlock_free() handle the case where ptdesc->ptl is >> NULL and remove VM_BUG_ON_PAGE() from pmd_ptlock_free(), we can unify >> pagetable_p*_dtor() into one function. Let's introduce pagetable_dtor() >> to do this. >> >> Later, pagetable_dtor() will be moved to tlb_remove_ptdesc(), so that >> ptlock and page table pages can be freed together (regardless of whether >> RCU is used). This prevents the use-after-free problem where the ptlock >> is freed immediately but the page table pages is freed later via RCU. >> >> Signed-off-by: Qi Zheng >> Originally-by: Peter Zijlstra (Intel) > ... >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index 5d82f42ddd5cc..cad11fa10c192 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -2992,6 +2992,15 @@ static inline bool ptlock_init(struct ptdesc *ptdesc) { return true; } >> static inline void ptlock_free(struct ptdesc *ptdesc) {} >> #endif /* defined(CONFIG_SPLIT_PTE_PTLOCKS) */ >> >> +static inline void pagetable_dtor(struct ptdesc *ptdesc) >> +{ >> + struct folio *folio = ptdesc_folio(ptdesc); >> + >> + ptlock_free(ptdesc); >> + __folio_clear_pgtable(folio); >> + lruvec_stat_sub_folio(folio, NR_PAGETABLE); >> +} >> + > > If I am not mistaken, it is just pagetable_pte_dtor() rename. > What is the point in moving the code around? No, this is to unify pagetable_p*_dtor() into pagetable_dtor(), so that we can move pagetable_dtor() to __tlb_remove_table(), and then ptlock and PTE page can be freed together through RCU, which is also the main purpose of this patch series. Thanks! > >> static inline bool pagetable_pte_ctor(struct ptdesc *ptdesc) >> { >> struct folio *folio = ptdesc_folio(ptdesc); >> @@ -3003,15 +3012,6 @@ static inline bool pagetable_pte_ctor(struct ptdesc *ptdesc) >> return true; >> } >> >> -static inline void pagetable_pte_dtor(struct ptdesc *ptdesc) >> -{ >> - struct folio *folio = ptdesc_folio(ptdesc); >> - >> - ptlock_free(ptdesc); >> - __folio_clear_pgtable(folio); >> - lruvec_stat_sub_folio(folio, NR_PAGETABLE); >> -} >> - >> pte_t *___pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp); >> static inline pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr, >> pmd_t *pmdvalp)