Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751922AbYAYA0k (ORCPT ); Thu, 24 Jan 2008 19:26:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751858AbYAYA0b (ORCPT ); Thu, 24 Jan 2008 19:26:31 -0500 Received: from gw.goop.org ([64.81.55.164]:47098 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753233AbYAYA0a (ORCPT ); Thu, 24 Jan 2008 19:26:30 -0500 Message-ID: <47992CB2.8050606@goop.org> Date: Thu, 24 Jan 2008 16:26:26 -0800 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.9 (X11/20071115) MIME-Version: 1.0 To: Nick Piggin CC: Matt Mackall , Harvey Harrison , Ingo Molnar , Linux Kernel Mailing List , Andi Kleen , Keir Fraser , Jan Beulich Subject: Re: [PATCH UPDATE] x86: ignore spurious faults References: <4797D64D.1060105@goop.org> <1201202046.3897.41.camel@cinder.waste.org> <4798E51C.4000209@goop.org> <200801251041.17392.nickpiggin@yahoo.com.au> In-Reply-To: <200801251041.17392.nickpiggin@yahoo.com.au> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1830 Lines: 46 Nick Piggin wrote: > On Friday 25 January 2008 06:21, Jeremy Fitzhardinge wrote: > >> Matt Mackall wrote: >> >>> There's perhaps an opportunity to do this lazy TLB trick in the mmap >>> path as well, where RW mappings are initially mapped as RO so we can >>> catch processes dirtying them and then switched to RW. If the mapping is >>> shared across threads on multiple cores, we can defer synchronizing the >>> TLBs on the others. >>> >> I think spurious usermode faults are already dealt with. >> handle_pte_fault() does essentially the same thing as this patch: >> >> if (ptep_set_access_flags(vma, address, pte, entry, write_access)) { >> update_mmu_cache(vma, address, entry); >> } else { >> /* >> * This is needed only for protection faults but the arch code >> * is not yet telling us if this is a protection fault or not. >> * This still avoids useless tlb flushes for .text page faults >> * with threads. >> */ >> if (write_access) >> flush_tlb_page(vma, address); >> } >> > > I (obviously) don't know exactly how the TLB works in x86, but I > thought that on a miss, the CPU walks the pagetables first before > faulting? Maybe that's not the case if there is an RO entry > actually in the TLB? > My understanding is that it will fault immediately if there's a TLB entry, and rewalk the tables on return from the fault before restarting the instruction, so there's no need for an explicit TLB flush. The TLB doesn't have a notion of negative cache entries, so any entry represents a present page of some variety. J -- 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/