From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [78.32.30.218]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7991018E377 for ; Fri, 13 Dec 2024 09:12:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=78.32.30.218 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734081135; cv=none; b=BNJeC6NBnPXnHIqf1xAFlMpwmGCl0jJIjSlrwn/WXlrZleYaJLU9Be3yYbCUwYewCij35OXvSBlRFMClMAuIr7a5GTvCV3nC0bHkeUfkIMlzUJt//T9JrU4YTi+RjwWY3PHpDt4napS2SgC9fM+lTpOWbgTiD3+0lWmDsbslTZc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734081135; c=relaxed/simple; bh=VJ575nUwPGTQW+bwAxw9vvuVQ+ajmPtkOr9brbpeR24=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Jkoymlrx/nJ0cQybPVBejO+V8Fpf9JzThCx6K8XmtA3imbf0imFonzKI0g1DdBlOOCZzW2nrjH+jTFXW8+x5oK7AtUAN2sqkd2KhmkeqDi5czE90WIgilIJ4ZY7bpanDNukgejloEKnCNFQp8JFHpCp+/1hvnp61XaQB14PSFYE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk; spf=none smtp.mailfrom=armlinux.org.uk; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b=QtmTa+Ke; arc=none smtp.client-ip=78.32.30.218 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="QtmTa+Ke" 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: Russell King (Oracle) 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!