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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 F3737E7717D for ; Fri, 13 Dec 2024 09:16:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=rka3uWrK3MCyr0hfJh0ffhr2Lty5KOVMuvd6Op+l+RM=; b=o5HwIlpTCwjB+10tXfnuMWDnTk Vb2kCCGtVNaODiNC/C4pgq+qa3RdJ4b7XBMqPzWjmsYppkcH6qxcZi3IVcPToGoZk7EQR+HNLP2WA JRqG7YfvCbzLQXnfxLJl2zUIPaSvoHbDiNOMGuP2Pv8HNHYQH3cvt+COuRq0hHhsxkmRJ7zsYNqDm KZ/0g9wtJ80FTJjuRPvwTgcMWsmob3K9rEO6lxqWXMwRT3lR/7o5IPheXiOqhMoVQaTyR15NJHURH nQfkkyB4RB/+Lic/0+HMqd20EVHQbl+X4qgzMQj5+jjVfoy8sLSp2WH6R5VHplPRVtxI4kRfggOLh 8uyHW1UQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tM1md-00000003DJQ-16Wd; Fri, 13 Dec 2024 09:16:27 +0000 Received: from pandora.armlinux.org.uk ([2001:4d48:ad52:32c8:5054:ff:fe00:142]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tM1kS-00000003CUf-2SCu for linux-arm-kernel@lists.infradead.org; Fri, 13 Dec 2024 09:14:13 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=rka3uWrK3MCyr0hfJh0ffhr2Lty5KOVMuvd6Op+l+RM=; b=QtmTa+KeLXA/34ueeEIk2NLJtK e7hFH4BPaIqy39ed3evrUQyqwf0ncaoLLu/euV8o6NkUoV+APH+fOMeEL//1+ABTuDcM31G/Mytyu IKtWDLOy3TrJMTSC1MQL4ny/IFUEht6RmD7gDS8usd1M0WLj2vlKVFGQZBPLHJxHQAXZde9vzKA3o gbeEQyud7Mz7uHmN6Xxc2j9HoEMybSa9gFuniaWT/pu90uQah4hwAbIEz8Xq2aLLIxH5APw3TdSSF NInxZKt+lWqgJKh6mKdij+rPbqRWPK2IUebz46lV+kAzDjqfprxUY1o94GOPtUejfNia8QdSHaOBy RUQ9DyRw==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:56840) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1tM1iM-0006SP-1N; Fri, 13 Dec 2024 09:12:02 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.96) (envelope-from ) id 1tM1iH-0006CT-0h; Fri, 13 Dec 2024 09:11:57 +0000 Date: Fri, 13 Dec 2024 09:11:57 +0000 From: "Russell King (Oracle)" To: Linus Walleij Cc: Sebastian Andrzej Siewior , Arnd Bergmann , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Arnd Bergmann , linux-mm@kvack.org, linux-rt-devel@lists.linux.dev, Ard Biesheuvel , Clark Williams , Jason Baron , Josh Poimboeuf , Mark Rutland , Matthew Wilcox , Peter Zijlstra , Steven Rostedt , David Hildenbrand Subject: Re: [PATCH 2/4] ARM: Disable HIGHPTE on PREEMPT_RT kernels Message-ID: References: <20241210160556.2341497-1-arnd@kernel.org> <20241210160556.2341497-3-arnd@kernel.org> <20241211152257.Igx3aT2Y@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241213_011412_613371_7C170E5A X-CRM114-Status: GOOD ( 20.08 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Dec 13, 2024 at 01:27:00AM +0100, Linus Walleij wrote: > On Wed, Dec 11, 2024 at 4:22 PM Sebastian Andrzej Siewior > wrote: > > On 2024-12-11 14:29:29 [+0100], Linus Walleij wrote: > > > So fast GUP is supposed to be lockless, and should just not > > > have this problem. So it can't be addressing gup_fast_pgd_range() > > > right? > > … > > > I'm more asking if HIGHPTE even acquires a spinlock anymore > > > as it is supposed to be "fast"/lockless. If it does, it is clearly violating > > > the "fast" promise of the fast GUP API and should not exist. > > > > This is lockless on x86. The problem is ARM's > > arch_kmap_local_high_get(). This is where the lock is from. > > Aha that calls down to kmap_high_get() that that issues > lock_kmap_any(flags). > > But is it really sound that the "fast" API does this? It feels > like a violation of the whole design of the fast stuff. If there's no way to do it lockless, then it has to take the lock. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!