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Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1pjj5O-00FV9O-TT; Tue, 04 Apr 2023 16:00:43 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 07BC4300202; Tue, 4 Apr 2023 18:00:39 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D69342CB6F7B0; Tue, 4 Apr 2023 18:00:38 +0200 (CEST) Date: Tue, 4 Apr 2023 18:00:38 +0200 From: Peter Zijlstra To: Yair Podemsky Cc: linux@armlinux.org.uk, mpe@ellerman.id.au, npiggin@gmail.com, christophe.leroy@csgroup.eu, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, davem@davemloft.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, will@kernel.org, aneesh.kumar@linux.ibm.com, akpm@linux-foundation.org, arnd@arndb.de, keescook@chromium.org, paulmck@kernel.org, jpoimboe@kernel.org, samitolvanen@google.com, frederic@kernel.org, ardb@kernel.org, juerg.haefliger@canonical.com, rmk+kernel@armlinux.org.uk, geert+renesas@glider.be, tony@atomide.com, linus.walleij@linaro.org, sebastian.reichel@collabora.com, nick.hawkins@hpe.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, mtosatti@redhat.com, vschneid@redhat.com, dhildenb@redhat.com, alougovs@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 Message-ID: <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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230404151217.GB297936@hirez.programming.kicks-ass.net> X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: 9tke8wo6mobrbasjonpja8ux7xgo4zwo X-Rspamd-Queue-Id: D4EBB1A005A X-HE-Tag: 1680624098-892977 X-HE-Meta: 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 J9Ubn16Z RX9ougirr9RlCguf82wVCtZo8+I4s9cZpsHRMFKvi+VnRF26x/gOmOHEH5PnhqLu0ulYhv1cm41svGCd3AeEzl0p5Nq6Ecg0vTOKwcKtu2XQ9QDOOxGfdtA/ZQFnAfhrD+Jcok8Tm8CK35X8fcBCNPvueH7fHuaPZ9ah5Kj/v5RBU+06Zu+iEEQd8uz3fPHi0Chq0d6kdsQPT47S/7oK8mv7BNzrF3SSRc1YOJRdbsihODG48Pyqi565nq8eZPZwKi1GN1dPOlnoC1FdMIgipRvWNgaQzX0WLZjHp 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, 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? On the state tracking side, we have ct_state_inc() which is atomic_add_return() which should provide full barrier and is sufficient.