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X-CSE-ConnectionGUID: k1wqFsvtRGukrPEoHF9jXA== X-CSE-MsgGUID: NjDi/TvsS0KP1QZv/vyYig== X-IronPort-AV: E=McAfee;i="6800,10657,11692"; a="88936902" X-IronPort-AV: E=Sophos;i="6.21,275,1763452800"; d="scan'208";a="88936902" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by orvoesa102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Feb 2026 09:00:36 -0800 X-CSE-ConnectionGUID: SZ/zc+FZTuCLeQ/2VCBFhg== X-CSE-MsgGUID: qZLHWbTlRJKp+O10ESL/Ww== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,275,1763452800"; d="scan'208";a="248191764" Received: from tfalcon-desk.amr.corp.intel.com (HELO [10.125.111.86]) ([10.125.111.86]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Feb 2026 09:00:35 -0800 Message-ID: <1dfde42a-838c-4dc5-8ea8-0b501df37af8@intel.com> Date: Thu, 5 Feb 2026 09:00:34 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 0/3] targeted TLB sync IPIs for lockless page table To: Lance Yang , "David Hildenbrand (Arm)" , Peter Zijlstra Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, aneesh.kumar@kernel.org, arnd@arndb.de, baohua@kernel.org, baolin.wang@linux.alibaba.com, boris.ostrovsky@oracle.com, bp@alien8.de, dave.hansen@linux.intel.com, dev.jain@arm.com, hpa@zytor.com, hughd@google.com, ioworker0@gmail.com, jannh@google.com, jgross@suse.com, kvm@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, mingo@redhat.com, npache@redhat.com, npiggin@gmail.com, pbonzini@redhat.com, riel@surriel.com, ryan.roberts@arm.com, seanjc@google.com, shy828301@gmail.com, tglx@linutronix.de, virtualization@lists.linux.dev, will@kernel.org, x86@kernel.org, ypodemsk@redhat.com, ziy@nvidia.com References: <20260202095414.GE2995752@noisy.programming.kicks-ass.net> <20260202110329.74397-1-lance.yang@linux.dev> <20260202125030.GB1395266@noisy.programming.kicks-ass.net> <4700e7ba-8456-4a93-9e28-7e5a3ca2a1be@linux.dev> <20260202133713.GF1395266@noisy.programming.kicks-ass.net> <540adec9-c483-460a-a682-f2076cf015c2@linux.dev> <20260202150957.GD1282955@noisy.programming.kicks-ass.net> <06d48a52-e4ec-47cd-b3fb-0fccd4dc49f4@kernel.org> <3026ad8d-92ad-4683-8c3e-733d4070d033@linux.dev> <64f3a75a-30ff-4bee-833c-be5dba05f72b@intel.com> <647cbe2e-a034-4a75-9492-21ea1708eccc@intel.com> <99237729-f2b0-4a7a-8213-65a2f1c57744@linux.dev> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Stat-Signature: cmkqwa136qzoxd19jqw1a4h865n9cbhy X-Rspam-User: X-Rspamd-Queue-Id: A7267C000A X-HE-Tag: 1770310837-540493 X-HE-Meta: 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 YTjafN7v rPgYAlTVQ41IzHbHOoKMZKKsuG385HfTnt0o3y4SmH7+YnvZafLuXFwII+nhNLIky0zvQWkHfJQ8IgAT/7J/ihRpiZBG7e01YyYhTfEw5nTybJswpgQDAmu0e+OnZvu7HWgZLqk9v8Vt+y55XGGmainUs7PVWO9nmtvKj8s51dRmZ9vTUFS57Cl6eFML5IxwN22lR 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 2/5/26 08:30, Lance Yang wrote: ... >> Are there cases where ongoing concurrent lockless page-table walks need >> to see the writes and they can't tolerate seeing valid but slightly >> stale data? > > The issue is we're about to free the page table (e.g. > pmdp_collapse_flush()). > > We have to ensure no walker is still doing a lockless page-table walk > when the page directories are freed, otherwise we get use-after-free. But isn't this already solved by the existing RCU freeing approach documented above tlb_remove_table_smp_sync()? This seems like a rather classic way to use RCU: wait to free until RCU says there can't be a reader any more. You don't have to sit there and wait for it, you just use call_rcu() which will hold off the free until it's safe.