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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E8D71C76188 for ; Wed, 5 Apr 2023 11:10:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230012AbjDELKN (ORCPT ); Wed, 5 Apr 2023 07:10:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46186 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231226AbjDELKM (ORCPT ); Wed, 5 Apr 2023 07:10:12 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0F3854EEE; Wed, 5 Apr 2023 04:10:12 -0700 (PDT) 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 9918463B9B; Wed, 5 Apr 2023 11:10:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 50CBBC433D2; Wed, 5 Apr 2023 11:10:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1680693010; bh=ooCH6+LbUpOMMrNQgOWug2YiY+jDptLepUBqEHzy38Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=u8LvHGP+e+G/tSvmxikKj2fPXrrk0+3vQGP+KsaklvN9YmbUCHGANHWv3q6iC5HtS fy9l0bjNgR3HG3KM+EASpjRNgn7dp0Q7ndpMhPFCq5T5lviAwsVYYN/imSlMEqcc7J Pi0w5XFSLGZbOcOsH4lPOKZHWzTs10xmPVp5WHoBvKxxjhceqhX9MI5gQG81P+MTe7 LUV9T7LzQ/XDpFte7PNV4zDO5W1rZBSwLnn10QDPGf1MrC31gIz37yW68z2ShgDqIe WrsUT0GI5Rjs9+Bf9sMLDspBq0Su2t5h8EXV4hbTo1QGErDk8Mc1BEdaH+mzYziPqY DTUnzQSCU4SjA== Date: Wed, 5 Apr 2023 13:10:07 +0200 From: Frederic Weisbecker 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, peterz@infradead.org, arnd@arndb.de, keescook@chromium.org, paulmck@kernel.org, jpoimboe@kernel.org, samitolvanen@google.com, 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 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: Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Wed, Apr 05, 2023 at 12:44:04PM +0200, Frederic Weisbecker wrote: > On Tue, Apr 04, 2023 at 04:42:24PM +0300, Yair Podemsky wrote: > > + 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? Bah, actually what can we do to prevent from that racy IPI? Not much I fear...