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 X-Spam-Level: X-Spam-Status: No, score=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 35803C433F4 for ; Wed, 29 Aug 2018 16:14:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E5228205C9 for ; Wed, 29 Aug 2018 16:14:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="bXLddv8i" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E5228205C9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729257AbeH2ULx (ORCPT ); Wed, 29 Aug 2018 16:11:53 -0400 Received: from merlin.infradead.org ([205.233.59.134]:55576 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727484AbeH2ULx (ORCPT ); Wed, 29 Aug 2018 16:11:53 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding: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=VlG+qIOjq4ELptMpQOsUdBOO02kYYhYCM6s2FctM1lA=; b=bXLddv8imDgdZ9qTIufJ1SqPC VbzVtnEYrOmswm8y01r86pFRRuqDXYqagCc7DVyyBnQayOiH1lm83IIn/tu6hfLGVTwhL9EwTdQKg 9d/zLtWl5XYrWODgxyJIBIgyh8USTDxUQVJlCI59ug6q+UDpg10CjCraC7UtJS89KGUgpZJVWpKX0 0kMmYA/AJ656WuJG0cx3c5amSKGj2LjOR4KHoOiRQx+da39+GcW0R6baITIZ1VATSCYYuuX1+WgCA em1GxL8iwDlfz0xOcTtlbjbVPv5R09ZEWKDExOhc52tg6WE59JwdSsXyFF83m4muIdkZ3kF/K4emj 87PDCBduA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fv36Y-0002z9-Ma; Wed, 29 Aug 2018 16:14:02 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 427A52024D700; Wed, 29 Aug 2018 18:14:00 +0200 (CEST) Date: Wed, 29 Aug 2018 18:14:00 +0200 From: Peter Zijlstra To: Andy Lutomirski Cc: Nadav Amit , Thomas Gleixner , LKML , Ingo Molnar , X86 ML , Arnd Bergmann , linux-arch , Masami Hiramatsu , Kees Cook , Dave Hansen Subject: Re: [RFC PATCH 5/6] x86/alternatives: use temporary mm for text poking Message-ID: <20180829161400.GV24124@hirez.programming.kicks-ass.net> References: <20180829081147.184610-1-namit@vmware.com> <20180829081147.184610-6-namit@vmware.com> <20180829092839.GP24124@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 29, 2018 at 08:46:04AM -0700, Andy Lutomirski wrote: > On Wed, Aug 29, 2018 at 2:28 AM, Peter Zijlstra wrote: > > On Wed, Aug 29, 2018 at 01:11:46AM -0700, Nadav Amit wrote: > > >> + pte_clear(poking_mm, poking_addr, ptep); > >> + > >> + /* > >> + * __flush_tlb_one_user() performs a redundant TLB flush when PTI is on, > >> + * as it also flushes the corresponding "user" address spaces, which > >> + * does not exist. > >> + * > >> + * Poking, however, is already very inefficient since it does not try to > >> + * batch updates, so we ignore this problem for the time being. > >> + * > >> + * Since the PTEs do not exist in other kernel address-spaces, we do > >> + * not use __flush_tlb_one_kernel(), which when PTI is on would cause > >> + * more unwarranted TLB flushes. > >> + */ > > > > yuck :-), but yeah. > > I'm sure we covered this ad nauseum when PTI was being developed, but > we were kind of in a rush, so: > > Why do we do INVPCID at all? The fallback path for non-INVPCID > systems uses invalidate_user_asid(), which should be faster than the > invpcid path. And doesn't do a redundant flush in this case. I don't remember; and you forgot to (re)add dhansen. Logically INVPCID_SINGLE should be faster since it pokes out a single translation in another PCID instead of killing all user translations. Is it just a matter of (current) chips implementing INVLPCID_SINGLE inefficient, or something else?