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Wed, 5 Apr 2023 19:45:57 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B72E940C6EC4; Wed, 5 Apr 2023 19:45:55 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id 8DE6240134449; Wed, 5 Apr 2023 16:45:32 -0300 (-03) Date: Wed, 5 Apr 2023 16:45:32 -0300 From: Marcelo Tosatti To: 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: 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: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 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, Yair Podemsky , 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, 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 Wed, Apr 05, 2023 at 01:10:07PM +0200, Frederic Weisbecker wrote: > 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... Use a different mechanism other than an IPI to ensure in progress __get_free_pages_fast() has finished execution. Isnt this codepath slow path enough that it can use synchronize_rcu_expedited?