Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932168AbVJYPAL (ORCPT ); Tue, 25 Oct 2005 11:00:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932169AbVJYPAL (ORCPT ); Tue, 25 Oct 2005 11:00:11 -0400 Received: from relais.videotron.ca ([24.201.245.36]:24106 "EHLO relais.videotron.ca") by vger.kernel.org with ESMTP id S932168AbVJYPAK (ORCPT ); Tue, 25 Oct 2005 11:00:10 -0400 Date: Tue, 25 Oct 2005 11:00:09 -0400 (EDT) From: Nicolas Pitre Subject: Re: [PATCH 2/9] mm: arm ready for split ptlock In-reply-to: <20051025075555.GA25020@flint.arm.linux.org.uk> X-X-Sender: nico@localhost.localdomain To: Russell King Cc: Hugh Dickins , Andrew Morton , linux-kernel@vger.kernel.org Message-id: MIME-version: 1.0 Content-type: TEXT/PLAIN; charset=US-ASCII Content-transfer-encoding: 7BIT References: <20051022170240.GA10631@flint.arm.linux.org.uk> <20051025075555.GA25020@flint.arm.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1731 Lines: 38 On Tue, 25 Oct 2005, Russell King wrote: > On Mon, Oct 24, 2005 at 10:45:04PM -0400, Nicolas Pitre wrote: > > On Sat, 22 Oct 2005, Russell King wrote: > > > Please contact Nicolas Pitre about that - that was my suggestion, > > > but ISTR apparantly the overhead is too high. > > > > Going through a kernel buffer will simply double the overhead. Let's > > suppose it should not be a big enough issue to stop the patch from being > > merged though (and it looks cleaner that way). However I'd like for the > > WARN_ON((unsigned long)frame & 7) to remain as both the kernel and user > > buffers should be 64-bit aligned. > > The WARN_ON is pointless because we guarantee that the stack is always > 64-bit aligned on signal handler setup and return. Sure, but the iWMMXt context is stored after the standard sigcontext which also must be 64 bits in size (which might not be always the case if things change in the structure or in its padding). > > I don't see how standard COW could not happen. The only difference with > > a true write fault as if we used put_user() is that we bypassed the data > > abort vector and the code to get the FAR value. Or am I missing > > something? > > pte_write() just says that the page _may_ be writable. It doesn't say > that the MMU is programmed to allow writes. If pte_dirty() doesn't > return true, that means that the page is _not_ writable from userspace. Argh... So only suffice to s/pte_write/pte_dirty/ I'd guess? Nicolas - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/