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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 0C061C54FCB for ; Sat, 25 Apr 2020 22:10:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CEA6320706 for ; Sat, 25 Apr 2020 22:10:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587852644; bh=xuqmIzDpOCho8iZFxLKt+Gkxw+5vPYAZTLSjtItPycU=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=e1l2IVEOMkdFO8q4QM8QWPVaWC/+V7KBwoqCABoFDKq5m3/QhHKL75SZtWMGqMvcI fzk+ROo1LFOORz6vo8/qn5YDD+kQrhOXSpLfWJR7yb1iztkwYSDCGMWsAc0tWoH23j j4om2ebXet54bKaYDBzJfAShBcT+sb3Z6n5WIM6g= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726359AbgDYWKn (ORCPT ); Sat, 25 Apr 2020 18:10:43 -0400 Received: from mail.kernel.org ([198.145.29.99]:60998 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726220AbgDYWKn (ORCPT ); Sat, 25 Apr 2020 18:10:43 -0400 Received: from mail-wr1-f46.google.com (mail-wr1-f46.google.com [209.85.221.46]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A1FBE21707 for ; Sat, 25 Apr 2020 22:10:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587852642; bh=xuqmIzDpOCho8iZFxLKt+Gkxw+5vPYAZTLSjtItPycU=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=VQq6Mz7smcr3zNIcC9pKupyHyFvsFY8q4jW93o4Pvp61DKtny6S1PN1CVtESTMt1x 0YOy/VXa+OfZBvFpSU6eteA54tRtaoUDqUeg9gPjIMkG43XV6c3n6wN2gXYsQk4uLU CqnubEshLb3LjDTEOxBI+/8+ibDs0pY1ir/VgnPY= Received: by mail-wr1-f46.google.com with SMTP id f13so15920628wrm.13 for ; Sat, 25 Apr 2020 15:10:42 -0700 (PDT) X-Gm-Message-State: AGi0PuYcua7VEg9rcGXJ/C5ppVCICWLpMtU3chXTDhdzI9NqFGnqk/u2 A8uBFPi19ZFVzCe948vnStP/brnxlTwvP4BFEBlKPA== X-Google-Smtp-Source: APiQypJY9gdxtTJ8GRawCUdcR1DxC8wlogE3i2vYIogcFwlTEoBRip4uY50PmovAxmm9X2kGA1bOgOh4cBwbd1QBjkA= X-Received: by 2002:a5d:62cc:: with SMTP id o12mr18433808wrv.75.1587852641044; Sat, 25 Apr 2020 15:10:41 -0700 (PDT) MIME-Version: 1.0 References: <20200425191032.GK21900@8bytes.org> <910AE5B4-4522-4133-99F7-64850181FBF9@amacapital.net> <20200425202316.GL21900@8bytes.org> In-Reply-To: <20200425202316.GL21900@8bytes.org> From: Andy Lutomirski Date: Sat, 25 Apr 2020 15:10:29 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] Allow RDTSC and RDTSCP from userspace To: Joerg Roedel Cc: Andy Lutomirski , Joerg Roedel , Dave Hansen , Tom Lendacky , Mike Stunes , Dan Williams , Dave Hansen , "H. Peter Anvin" , Juergen Gross , Jiri Slaby , Kees Cook , kvm list , LKML , Peter Zijlstra , Thomas Hellstrom , Linux Virtualization , X86 ML , Sean Christopherson Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Apr 25, 2020 at 1:23 PM Joerg Roedel wrote: > > On Sat, Apr 25, 2020 at 12:47:31PM -0700, Andy Lutomirski wrote: > > I assume the race you mean is: > > > > #VC > > Immediate NMI before IST gets shifted > > #VC > > > > Kaboom. > > > > How are you dealing with this? Ultimately, I think that NMI will need > > to turn off IST before engaging in any funny business. Let me ponder > > this a bit. > > Right, I dealt with that by unconditionally shifting/unshifting the #VC IST entry > in do_nmi() (thanks to Davin Kaplan for the idea). It might cause > one of the IST stacks to be unused during nesting, but that is fine. The > stack memory for #VC is only allocated when SEV-ES is active (in an > SEV-ES VM). Blech. It probably works, but still, yuck. It's a bit sad that we seem to be growing more and more poorly designed happens-anywhere exception types at an alarming rate. We seem to have #NM, #MC, #VC, #HV, and #DB. This doesn't really scale. --Andy