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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 27AFDC761A6 for ; Wed, 5 Apr 2023 10:44:57 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4Ps1VH3f5Hz3cgT for ; Wed, 5 Apr 2023 20:44:55 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=RfEi0EWH; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=139.178.84.217; helo=dfw.source.kernel.org; envelope-from=frederic@kernel.org; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20201202 header.b=RfEi0EWH; dkim-atps=neutral Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4Ps1TK65hmz3c6Y for ; Wed, 5 Apr 2023 20:44:05 +1000 (AEST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 0DD036247E; Wed, 5 Apr 2023 10:44:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BFC61C433EF; Wed, 5 Apr 2023 10:44:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1680691441; bh=+ZO/yBxfJv0GaHczUgdJTBFHBjfQ/ykADeJttq42HmQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=RfEi0EWHrVtgDNTDmAkQHpOA1xGMHUdirDcpsD08NWpiRE8In3RAHPfhmz+mLo3Re keFWgaWXAHpSzJgLMWdEzHtCNaP6XaC77hbIAZwK+4PpDX/Zwb9pTItZlq4DbE4Bcj gF37NoMLKD33dyuHM4yV5O3ouVk+s6lLupFGmAHvGBDdJp1MrGsgJ5ZzVLp7GXS7g2 UIOMTpAu0+CUNt+73VKyRli+76KWSC33YcG5QeaD76fiXSWmghliODfhBl98LZE/dA PhaBHuqHXYQ037jMpcPmRNTtYCqZtKeIbh0pk5/nikjbQBZDel/38qAxiwMpnOZnDc uqZAC/jHMG+Ow== Date: Wed, 5 Apr 2023 12:43:58 +0200 From: Frederic Weisbecker To: Yair Podemsky Subject: Re: [PATCH 3/3] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to CPUs in kernel mode Message-ID: References: <20230404134224.137038-1-ypodemsk@redhat.com> <20230404134224.137038-4-ypodemsk@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230404134224.137038-4-ypodemsk@redhat.com> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: geert+renesas@glider.be, peterz@infradead.org, linus.walleij@linaro.org, dave.hansen@linux.intel.com, sebastian.reichel@collabora.com, linux-mm@kvack.org, hpa@zytor.com, sparclinux@vger.kernel.org, agordeev@linux.ibm.com, will@kernel.org, ardb@kernel.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, vschneid@redhat.com, arnd@arndb.de, paulmck@kernel.org, aneesh.kumar@linux.ibm.com, x86@kernel.org, linux@armlinux.org.uk, tony@atomide.com, mingo@redhat.com, samitolvanen@google.com, borntraeger@linux.ibm.com, keescook@chromium.org, gor@linux.ibm.com, hca@linux.ibm.com, npiggin@gmail.com, rmk+kernel@armlinux.org.uk, bp@alien8.de, nick.hawkins@hpe.com, tglx@linutronix.de, jpoimboe@kernel.org, linux-arm-kernel@lists.infradead.org, alougovs@redhat.com, mtosatti@redhat.com, linux-kernel@vger.kernel.org, juerg.haefliger@canonical.com, svens@linux.ibm.com, dhildenb@redhat.com, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, davem@davemloft.net Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Apr 04, 2023 at 04:42:24PM +0300, Yair Podemsky wrote: > @@ -191,6 +192,20 @@ static void tlb_remove_table_smp_sync(void *arg) > /* Simply deliver the interrupt */ > } > > + > +#ifdef CONFIG_CONTEXT_TRACKING > +static bool cpu_in_kernel(int cpu, void *info) > +{ > + struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu); Like Peter said, an smp_mb() is required here before the read (unless there is already one between the page table modification and that ct->state read?). So that you have this pairing: WRITE page_table WRITE ct->state smp_mb() smp_mb() // implied by atomic_fetch_or READ ct->state READ page_table > + int state = atomic_read(&ct->state); > + /* will return true only for cpus in kernel space */ > + return state & CT_STATE_MASK == CONTEXT_KERNEL; > +} Also note that this doesn't stricly prevent userspace from being interrupted. You may well observe the CPU in kernel but it may receive the IPI later after switching to userspace. We could arrange for avoiding that with marking ct->state with a pending work bit to flush upon user entry/exit but that's a bit more overhead so I first need to know about your expectations here, ie: can you tolerate such an occasional interruption or not? Thanks.