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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 6795DC43143 for ; Tue, 2 Oct 2018 11:39:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 127E0206B2 for ; Tue, 2 Oct 2018 11:39:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 127E0206B2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com 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 S1727537AbeJBSVu (ORCPT ); Tue, 2 Oct 2018 14:21:50 -0400 Received: from mx2.suse.de ([195.135.220.15]:53118 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727471AbeJBSVu (ORCPT ); Tue, 2 Oct 2018 14:21:50 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id E0AE7AEE6; Tue, 2 Oct 2018 11:38:56 +0000 (UTC) Subject: Re: [tip:x86/hyperv] x86/hyperv: Enable PV qspinlock for Hyper-V To: linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@kernel.org, sthemmin@microsoft.com, mikelley@microsoft.com, kys@microsoft.com, haiyangz@microsoft.com, yi.y.sun@linux.intel.com, hpa@zytor.com References: <1538028104-114050-3-git-send-email-yi.y.sun@linux.intel.com> From: Juergen Gross Openpgp: preference=signencrypt Autocrypt: addr=jgross@suse.com; prefer-encrypt=mutual; keydata= xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOB ycWxw3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJve dYm8Of8Zd621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJ NwQpd369y9bfIhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvx XP3FAp2pkW0xqG7/377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEB AAHNHkp1ZXJnZW4gR3Jvc3MgPGpncm9zc0BzdXNlLmRlPsLAeQQTAQIAIwUCU4xw6wIbAwcL CQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJELDendYovxMvi4UH/Ri+OXlObzqMANruTd4N zmVBAZgx1VW6jLc8JZjQuJPSsd/a+bNr3BZeLV6lu4Pf1Yl2Log129EX1KWYiFFvPbIiq5M5 kOXTO8Eas4CaScCvAZ9jCMQCgK3pFqYgirwTgfwnPtxFxO/F3ZcS8jovza5khkSKL9JGq8Nk czDTruQ/oy0WUHdUr9uwEfiD9yPFOGqp4S6cISuzBMvaAiC5YGdUGXuPZKXLpnGSjkZswUzY d9BVSitRL5ldsQCg6GhDoEAeIhUC4SQnT9SOWkoDOSFRXZ+7+WIBGLiWMd+yKDdRG5RyP/8f 3tgGiB6cyuYfPDRGsELGjUaTUq3H2xZgIPfOwE0EU4xwFgEIAMsx+gDjgzAY4H1hPVXgoLK8 B93sTQFN9oC6tsb46VpxyLPfJ3T1A6Z6MVkLoCejKTJ3K9MUsBZhxIJ0hIyvzwI6aYJsnOew cCiCN7FeKJ/oA1RSUemPGUcIJwQuZlTOiY0OcQ5PFkV5YxMUX1F/aTYXROXgTmSaw0aC1Jpo w7Ss1mg4SIP/tR88/d1+HwkJDVW1RSxC1PWzGizwRv8eauImGdpNnseneO2BNWRXTJumAWDD pYxpGSsGHXuZXTPZqOOZpsHtInFyi5KRHSFyk2Xigzvh3b9WqhbgHHHE4PUVw0I5sIQt8hJq 5nH5dPqz4ITtCL9zjiJsExHuHKN3NZsAEQEAAcLAXwQYAQIACQUCU4xwFgIbDAAKCRCw3p3W KL8TL0P4B/9YWver5uD/y/m0KScK2f3Z3mXJhME23vGBbMNlfwbr+meDMrJZ950CuWWnQ+d+ Ahe0w1X7e3wuLVODzjcReQ/v7b4JD3wwHxe+88tgB9byc0NXzlPJWBaWV01yB2/uefVKryAf AHYEd0gCRhx7eESgNBe3+YqWAQawunMlycsqKa09dBDL1PFRosF708ic9346GLHRc6Vj5SRA UTHnQqLetIOXZm3a2eQ1gpQK9MmruO86Vo93p39bS1mqnLLspVrL4rhoyhsOyh0Hd28QCzpJ wKeHTd0MAWAirmewHXWPco8p1Wg+V+5xfZzuQY0f4tQxvOpXpt4gQ1817GQ5/Ed/wsDtBBgB CAAgFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAlrd8NACGwIAgQkQsN6d1ii/Ey92IAQZFggA HRYhBFMtsHpB9jjzHji4HoBcYbtP2GO+BQJa3fDQAAoJEIBcYbtP2GO+TYsA/30H/0V6cr/W V+J/FCayg6uNtm3MJLo4rE+o4sdpjjsGAQCooqffpgA+luTT13YZNV62hAnCLKXH9n3+ZAgJ RtAyDWk1B/0SMDVs1wxufMkKC3Q/1D3BYIvBlrTVKdBYXPxngcRoqV2J77lscEvkLNUGsu/z W2pf7+P3mWWlrPMJdlbax00vevyBeqtqNKjHstHatgMZ2W0CFC4hJ3YEetuRBURYPiGzuJXU pAd7a7BdsqWC4o+GTm5tnGrCyD+4gfDSpkOT53S/GNO07YkPkm/8J4OBoFfgSaCnQ1izwgJQ jIpcG2fPCI2/hxf2oqXPYbKr1v4Z1wthmoyUgGN0LPTIm+B5vdY82wI5qe9uN6UOGyTH2B3p hRQUWqCwu2sqkI3LLbTdrnyDZaixT2T0f4tyF5Lfs+Ha8xVMhIyzNb1byDI5FKCb Message-ID: <0005fc50-4415-87a0-1954-fb15a1f8bd0b@suse.com> Date: Tue, 2 Oct 2018 13:38:55 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sorry for noticing this only now, but I have been fighting with Xen PV qspinlocks last weekend: On 02/10/2018 13:28, tip-bot for Yi Sun wrote: > Commit-ID: aaa7fc34c003bd8133a49f7634480cef6288ad55 > Gitweb: https://git.kernel.org/tip/aaa7fc34c003bd8133a49f7634480cef6288ad55 > Author: Yi Sun > AuthorDate: Thu, 27 Sep 2018 14:01:44 +0800 > Committer: Thomas Gleixner > CommitDate: Tue, 2 Oct 2018 13:22:06 +0200 > > x86/hyperv: Enable PV qspinlock for Hyper-V > > Implement the necessary callbacks for PV spinlocks which allow vCPU idling > and kicking operations when running as a guest on Hyper-V > > Signed-off-by: Yi Sun > Signed-off-by: Thomas Gleixner > Reviewed-by: Michael Kelley > Cc: chao.p.peng@intel.com > Cc: chao.gao@intel.com > Cc: isaku.yamahata@intel.com > Cc: tianyu.lan@microsoft.com > Cc: "K. Y. Srinivasan" > Cc: Haiyang Zhang > Cc: Stephen Hemminger > Link: https://lkml.kernel.org/r/1538028104-114050-3-git-send-email-yi.y.sun@linux.intel.com > --- > Documentation/admin-guide/kernel-parameters.txt | 5 ++ > arch/x86/hyperv/Makefile | 4 ++ > arch/x86/hyperv/hv_spinlock.c | 75 +++++++++++++++++++++++++ > arch/x86/include/asm/mshyperv.h | 1 + > arch/x86/kernel/cpu/mshyperv.c | 14 +++++ > 5 files changed, 99 insertions(+) > ... > diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c > new file mode 100644 > index 000000000000..6d3221322d0d > --- /dev/null > +++ b/arch/x86/hyperv/hv_spinlock.c > @@ -0,0 +1,75 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +/* > + * Hyper-V specific spinlock code. > + * > + * Copyright (C) 2018, Intel, Inc. > + * > + * Author : Yi Sun > + */ > + > +#define pr_fmt(fmt) "Hyper-V: " fmt > + > +#include > + > +#include > +#include > +#include > +#include > +#include > + > +static bool __initdata hv_pvspin = true; > + > +static void hv_qlock_kick(int cpu) > +{ > + apic->send_IPI(cpu, X86_PLATFORM_IPI_VECTOR); > +} > + > +static void hv_qlock_wait(u8 *byte, u8 val) > +{ > + unsigned long msr_val; > + > + if (READ_ONCE(*byte) != val) > + return; > + > + /* > + * Read HV_X64_MSR_GUEST_IDLE MSR can trigger the guest's > + * transition to the idle power state which can be exited > + * by an IPI even if IF flag is disabled. > + */ What if interrupts are enabled? Won't a kick happening here just interrupt and then the following rdmsr result in a hang? I believe the correct way would be to: - disable interrupts before above READ_ONCE() and restore them after the rdmsrl() - return early if in_nmi() similar as the kvm specific variant is doing it. Juergen