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imf15.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf15.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.20 as permitted sender) smtp.mailfrom=hdanton@sina.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1680656002; a=rsa-sha256; cv=none; b=eMbHmooF4v6bDKz6XjeWk+XJGHdro++qmYSxyGRiGTZDv4J1Y7fEyBtkxF6eCvYfk9TY/2 WCGrgseZFV44dPiaqPA2XETsxHAdAcWa1wOg/3DyI3H9kAl/DTZiAwiUrlU+N+shKGth0t RW2HKVzCWZQDxpXWhJjtFFxUkwUwAbo= X-SMAIL-HELO: localhost.localdomain Received: from unknown (HELO localhost.localdomain)([114.249.59.75]) by sina.com (172.16.97.35) with ESMTP id 642CC64600020440; Wed, 5 Apr 2023 08:52:23 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 57372015073570 From: Hillf Danton To: Yair Podemsky Cc: Peter Zijlstra , npiggin@gmail.com, dave.hansen@linux.intel.com, will@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, dhildenb@redhat.com, Frederic Weisbecker Subject: Re: [PATCH 3/3] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to CPUs in kernel mode Date: Wed, 5 Apr 2023 08:53:07 +0800 Message-Id: <20230405005307.675-1-hdanton@sina.com> In-Reply-To: <20230404160038.GB38236@hirez.programming.kicks-ass.net> References: <20230404134224.137038-1-ypodemsk@redhat.com> <20230404134224.137038-4-ypodemsk@redhat.com> <20230404151217.GB297936@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 61039A000F X-Stat-Signature: wzggz7wpnuamqtajxnd4nxicmo39a7u7 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1680655999-768199 X-HE-Meta: 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 I4yghvOg /ffThvOxbe2eZ1XN7wRyqCIgiBe2x+O7C+YZN5UDCZ7JXYZGW2/Qew2Jt7criPSDfpL0Tarc3ATrcwuZWCOVx+4CT4gIijHKPHoPPEz88dyL7dofTpWff5gwLYmonL11i2hLQlGe3+D5LlycXGvrn9vvFgAJuk6D1bMmJafXG9X0u/jpXLVuvJJQD1iR5o07kG/0ECVXxl8y+DDQ= 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: On Tue, 4 Apr 2023 18:00:38 +0200 Peter Zijlstra > On Tue, Apr 04, 2023 at 05:12:17PM +0200, Peter Zijlstra wrote: > > > case 2: > > > CPU-A CPU-B > > > > > > modify pagetables > > > tlb_flush (memory barrier) > > > state == CONTEXT_USER > > > int state = atomic_read(&ct->state); > > > Kernel-enter: > > > state == CONTEXT_KERNEL > > > READ(pagetable values) > > > if (state & CT_STATE_MASK == CONTEXT_USER) > > > > > Hmm, hold up; what about memory ordering, we need a store-load ordering > between the page-table write and the context trackng load, and a > store-load order on the context tracking update and software page-table > walker loads. > > Now, iirc page-table modification is done under pte_lock (or > page_table_lock) and that only provides a RELEASE barrier on this end, > which is insufficient to order against a later load. > > Is there anything else? Hmm Yair could you specify what you meant by the memory barrier after tlb_flush in the diagram above? > > On the state tracking side, we have ct_state_inc() which is > atomic_add_return() which should provide full barrier and is sufficient.