From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 668C8C8303B for ; Thu, 29 Aug 2024 10:59:35 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C26536B0099; Thu, 29 Aug 2024 06:59:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BCA476B009A; Thu, 29 Aug 2024 06:59:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A6AD26B009B; Thu, 29 Aug 2024 06:59:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 8841E6B0099 for ; Thu, 29 Aug 2024 06:59:34 -0400 (EDT) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 31E39C0BE0 for ; Thu, 29 Aug 2024 10:59:34 +0000 (UTC) X-FDA: 82504987068.09.4CBA1B4 Received: from mail-pf1-f174.google.com (mail-pf1-f174.google.com [209.85.210.174]) by imf30.hostedemail.com (Postfix) with ESMTP id E225A80007 for ; Thu, 29 Aug 2024 10:59:30 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=bytedance.com header.s=google header.b=GXXtlnnF; spf=pass (imf30.hostedemail.com: domain of zhengqi.arch@bytedance.com designates 209.85.210.174 as permitted sender) smtp.mailfrom=zhengqi.arch@bytedance.com; dmarc=pass (policy=quarantine) header.from=bytedance.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1724929102; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=AkCs8X+rOG2k0a+0P5TyFf8pKHMHEP/2u//VabkdfQg=; b=15gixmyr0+Btiga6xZsrBSlW5rMV2E7ZTapCBNbvktN4NnoOqsoK+DC+JIT+fC0djJ19Gz XmE5nISQyiS+VtV1Mq1DNF3UrOSqHXXrfM5IqZAhhT0tQUo33cEo8JJe4XBAL8OE91tvPX GiEHZRXsfKdibiKYOMOx7De8xxgvmSg= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=bytedance.com header.s=google header.b=GXXtlnnF; spf=pass (imf30.hostedemail.com: domain of zhengqi.arch@bytedance.com designates 209.85.210.174 as permitted sender) smtp.mailfrom=zhengqi.arch@bytedance.com; dmarc=pass (policy=quarantine) header.from=bytedance.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1724929102; a=rsa-sha256; cv=none; b=so4Wz8d6eP4qaaPQg+pMNFd2P+XU2xcwTDnRhzZdNIehmwkprtcn1FBE+N9ZZ40t2woJ6t nmfvr1XUCM5yRy+dNrLYQ15U0jdcjDPv//030QWmuGKTvGUAVExufitVAH4AyW/3a0l50f ndefvLkB/PtXTF6bLvu0KQcW557DDNg= Received: by mail-pf1-f174.google.com with SMTP id d2e1a72fcca58-715e3e03831so483631b3a.2 for ; Thu, 29 Aug 2024 03:59:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance.com; s=google; t=1724929169; x=1725533969; darn=kvack.org; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=AkCs8X+rOG2k0a+0P5TyFf8pKHMHEP/2u//VabkdfQg=; b=GXXtlnnFnsZ4PNGXD/bObDlrcebBC7SILe2M2t9Sq1YV+Stywoi/zNuk2nxsgeFMGs fabwqljsd/2PqdEfiW0gRk3nBcBznDBVjd6kbE209lHMEDb6xtrf00yHCAFykOlT6nDA HlndHyFaPsNAej6p5IHvvEhDQycAeJElyvXC3P5tGcQp68pfDFNViKcFuMV5/sDlTbd3 dCDjJCI9RKCTYB+hacIT2rxejwAvxbzdJjP/pc/1ublvlNYrZrrAbDUpdEh4psWb4NQ2 a3phqMoNjkADrE1VT1aVso7v6PS7j3eGG/hOnuBQQ9/U+G3SGEcoTB9oJ8Mnc6csukyw /zqw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1724929169; x=1725533969; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=AkCs8X+rOG2k0a+0P5TyFf8pKHMHEP/2u//VabkdfQg=; b=FkW5IEWC+iLpwVdZTuojaEZaQeLITtDzOu6o0nYg2xArWwnWALgz32Q2ofYg3FyurL SgMw5oLOmLdkIxt/sU1Jwb5b7zlYudv/3b57vieerBXkBh5IURXIRtI+fQxXOdkmiihx oM47aDQkL5wiI8kSIyZX33NtLgJ+GONNLdT0yNcQsc80cgpFF+4eirXmV2cdG6vYME2n Qa1yBgEWy0ZZyI95tb6IRuX56e/j3qC9DglmYlrFqn21TFAFK6eGUeMtOqCrkZ1PBXDs jR82jBfNOVtsAZGAa4kHN/cnQqjrMZOf/Iwz+ODKNSnnO8XuS7w8E/KgYtQ9e8pPspsH E8LA== X-Forwarded-Encrypted: i=1; AJvYcCVVQ+bXc3hUEYc3vQZk4+0zDeHkzkCkg/iiMe96nwVZPwqwTdOyqe6mM27ZXLs47+HuWP9BZmJ/dQ==@kvack.org X-Gm-Message-State: AOJu0Yzrz3ZL+YVJZJkioLugQrNofO1rZ/dATBTIkDdgqSLcuQ3TjqXQ WJB50a29zpd047dbhMd1OGlp0IXj/4QOs5O+ao163fi5kIvza4iCaFfN1wttyLM= X-Google-Smtp-Source: AGHT+IHFavp3iD65n8I4MxM7X0z+O7YmVJGdY6pd4itbZCENaYUbQg/MTJWkKQgP47jm0Y5MTqQ9gg== X-Received: by 2002:a05:6a20:6f08:b0:1c6:ae03:6607 with SMTP id adf61e73a8af0-1cce0feac29mr2109334637.6.1724929169241; Thu, 29 Aug 2024 03:59:29 -0700 (PDT) Received: from [10.4.59.158] ([139.177.225.242]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-715e57629f4sm881857b3a.205.2024.08.29.03.59.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 Aug 2024 03:59:28 -0700 (PDT) Message-ID: <63ef0611-50c2-49b5-ba3f-c6ea81f9fbce@bytedance.com> Date: Thu, 29 Aug 2024 18:59:21 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 01/14] mm: pgtable: introduce pte_offset_map_{ro|rw}_nolock() Content-Language: en-US To: David Hildenbrand , muchun.song@linux.dev Cc: hughd@google.com, willy@infradead.org, vbabka@kernel.org, akpm@linux-foundation.org, rppt@kernel.org, vishal.moola@gmail.com, peterx@redhat.com, ryan.roberts@arm.com, christophe.leroy2@cs-soprasteria.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org References: <4481a0e4-a7a5-4223-a8ab-d1215d7c6352@bytedance.com> <42aba316-2b01-4fdb-9aff-9e670aac4c6e@redhat.com> From: Qi Zheng In-Reply-To: <42aba316-2b01-4fdb-9aff-9e670aac4c6e@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: 3xcobcikzbrbd4incidzoetwzdb6jwgr X-Rspam-User: X-Rspamd-Queue-Id: E225A80007 X-Rspamd-Server: rspam02 X-HE-Tag: 1724929170-921363 X-HE-Meta: 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 5dUbSiuF 1lV5aXBIzzuKkB9MqGthfMWIQCdaODCM7tm4XK9KwCf0ZKboTI8kc6VTsnnx5iGjSceWJ7VbtZkGjz1IuNiIXc22WUE88kCLU09A81nHulxAf5kIO/hEAhgqoX4tohV6WsAMnyrTbPP3nwcFik4svUSD1sKwyQ33uEBGPtiRQOEbRCDkwUIMa6+QMfBoVRRXfTxqamdQwIbUmRsxra+F68wiOQUloZHk2/YXNNhiTZyc/euNSGizwZ7VacgmNrb2dnEsA5eo7s/GoUFydJeRk1O+KkT0OG9lcV14MmShxeXhJeevU0ylx15MMus0o+GCCm1BxucGnBztpDWKap/W0QEoM/iEhRAaUlsqhSpum+2CsPIDd0gRk/c00lfMSX3o8Z1fXgBVjSEy8T+gjqIH0wLFXVxmTAUfayfzIMtvp6ZTm431IeuaZ9HNyj/TzT2EwxcwLF4g8NVM1u3M= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024/8/28 18:48, David Hildenbrand wrote: > On 27.08.24 06:33, Qi Zheng wrote: [...] >> sufficient AFAIUK. > > Drop the "AFAIUK" :) > > "For R/O access this is sufficient." > >> >> pte_offset_map_rw_nolock(mm, pmd, addr, pmdvalp, ptlp), above, is like >> pte_offset_map_ro_nolock(); but when successful, it also outputs the >> pdmval. For R/W access, the callers can not accept that the page table >> it sees has been unmapped and is about to get freed. The pmdval can help >> callers to recheck pmd_same() to identify this case once the spinlock is >> taken. For some cases where exclusivity is already guaranteed, such as >> holding the write lock of mmap_lock, or in cases where checking is >> sufficient, such as a !pte_none() pte will be rechecked after the >> spinlock is taken, there is no need to recheck pdmval. > > Right, using pte_same() one can achieve a similar result, assuming that > the freed page table gets all ptes set to pte_none(). > > page_table_check_pte_clear_range() before pte_free_defer() in > retract_page_tables/collapse_pte_mapped_thp() sanity checks that I think. Since commit 1d65b771bc08, retract_page_tables() only holds the i_mmap_lock_read(mapping) but not mmap_lock, so it seems that holding the write lock of mmap_lock cannot guarantee the stability of the PTE page. IIUC, I will also perform a pmd_same() check on the case where the write lock of mmap_lock is held in v3. Or do I miss something? > > In collapse_huge_page() that is not the case. But here, we also > currently grab all heavily locks, to prevent any concurrent page table > walker. > >> >> Note: "RO" / "RW" expresses the intended semantics, not that the *kmap* >> will be RO/RW protected. > > > Good. Please also incorporate the feedback from Muchun. >