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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,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 E83F3C43381 for ; Thu, 21 Mar 2019 18:37:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BB81F21902 for ; Thu, 21 Mar 2019 18:37:53 +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="ExTsKiAZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728744AbfCUShw (ORCPT ); Thu, 21 Mar 2019 14:37:52 -0400 Received: from merlin.infradead.org ([205.233.59.134]:38104 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728567AbfCUShw (ORCPT ); Thu, 21 Mar 2019 14:37:52 -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=6VaYjeQs3ztnvnR2zRnxFXXmqZ0mf8vhhYUVX1thu2w=; b=ExTsKiAZhNYMdyCWJYWBfM9u/ IUVSl4aRgPoCTeuP73DDKKZ9VU0vng0XIlYurPNZ5hPJTOu9Iu/1hJ5fcqGd5COSflQSkVhmpibaI VxIhDhTXZGjL/3kxJ82Km0c0Lv1rq7a5uUjqbjn9HRvl5yz4YxxfOYbr+B5pmsz9TEDPNgvdi/TWu yWrVSt0NV/hKmHahzgHH4KBrv+VvbwCNQCD7VdCGIkHDy/gash3LcLLgAXAMX+A8rARwUNRjmA07B PRB16n4ICO2vFl45JhPk0oM6nvpeDOdM/+8po+rnabKT7MpzgrkLKukGE7yVuduGL+E/zOrXqgVtg dGH5JRKog==; 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 1h72Z1-0001da-F0; Thu, 21 Mar 2019 18:37:15 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E9A4D203CBE11; Thu, 21 Mar 2019 19:37:13 +0100 (CET) Date: Thu, 21 Mar 2019 19:37:13 +0100 From: Peter Zijlstra To: Linus Torvalds Cc: Andy Lutomirski , Andrew Cooper , Jan Beulich , Boris Ostrovsky , Juergen Gross , Stefano Stabellini , Steven Rostedt , LKML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Joel Fernandes , He Zhe Subject: Re: [RFC][PATCH] tracing/x86: Save CR2 before tracing irqsoff on error_entry Message-ID: <20190321183713.GX5996@hirez.programming.kicks-ass.net> References: <20190320221534.165ab87b@oasis.local.home> <20190321083317.GL6058@hirez.programming.kicks-ass.net> <20190321090241.GL6521@hirez.programming.kicks-ass.net> <20190321104517.GM6521@hirez.programming.kicks-ass.net> <20190321093242.4a948198@gandalf.local.home> <20190321172203.GS5996@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/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 21, 2019 at 11:25:44AM -0700, Linus Torvalds wrote: > On Thu, Mar 21, 2019 at 11:21 AM Andy Lutomirski wrote: > > > > I dunno. Lots of people at least use to have serious commercial interest in it. > > Yes, it used to be a big deal. But full virtualization has gotten a > lot more common and better. > > > Hey Xen folks, how close are we to being able to say "if you want to > > run a new kernel, you need to switch to PVH or similar"? > > I'd also like to know if we could perhaps at least limit PV to just > the thing that people care most deeply about. > > For example, maybe people notice that they really deeply care about > the PV spinlocks because they help a lot for some loads, but don't > care so much about the low-level CPU PV stuff any more because modern > CPUs do _those_ things so well these days. > > So it might not be an all-or-nothing thing, but a gradual "let's stop > supporting xyz under PV, because it causes pain and isn't worth it". So Juergen recently introduced PARAVIRT_XXL, which are exactly those bits of PV we can get rid of. This paravirt-me-harder config does indeed include the CR2 bits. I recently talked to Andrew Cooper about this, and he said Xen Dom0 still needs all this :/ But yes, I'd _love_ to delete all that in a hurry.