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=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 9719BC31E4B for ; Fri, 14 Jun 2019 21:36:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7854520850 for ; Fri, 14 Jun 2019 21:36:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726063AbfFNVgN (ORCPT ); Fri, 14 Jun 2019 17:36:13 -0400 Received: from mail-wr1-f65.google.com ([209.85.221.65]:43552 "EHLO mail-wr1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726028AbfFNVgN (ORCPT ); Fri, 14 Jun 2019 17:36:13 -0400 Received: by mail-wr1-f65.google.com with SMTP id p13so3916162wru.10 for ; Fri, 14 Jun 2019 14:36:11 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=bCvKwbWJesvWCy0sKuZ4V0I/xR2OhzdiNEAy87dgHgM=; b=BIE9AEq1cU2Tez1u6RByDZrRQ7xoVwFfh2zvXrUKcxQRtuBmNA2qtA5iLhoZODcv0c 7klm/ZMqn0x4NY3U+HY8Rq6Gm45aF77XxZRulhyZUr5a9k7uzUGC/LyNqJ/2NwbF1NRa Xhu3sHWANX2Ka7PXB8yXnQ5k1Gye3pAE1Veec4zg9Cs/1eSRAHg2RKLy1olGEv+LFYhZ R/Vss0pTYEY1SFS4JzNX/O2X8tiCJ5PdlG02K3Rb9Ki/brvy3Mx/LmTvgD+OAC4M9zLw PcMfd82DvrYAvVoFQCPePi4De3A4IkncdhJ8cTgS0yQxNF0Wsj0ZqTalK/n1Ci0wAvQr ioWw== X-Gm-Message-State: APjAAAVYARFRtFsOWM+cWGX1HOF9X/W43ifST+XWSHvW3K+s+ubrhoOB TTceE/hoXGfOyb8SzBEPBrcb4w== X-Google-Smtp-Source: APXvYqyaz9SMMAfY94vjBsF6aHQAfX+3a3A9OUyl0nhTjKgPhD32zJqRx7RQJvJahMVOLtJk25eU4Q== X-Received: by 2002:a5d:500d:: with SMTP id e13mr3847025wrt.337.1560548171165; Fri, 14 Jun 2019 14:36:11 -0700 (PDT) Received: from vitty.brq.redhat.com (ip-78-102-201-117.net.upcbroadband.cz. [78.102.201.117]) by smtp.gmail.com with ESMTPSA id y6sm2905993wma.6.2019.06.14.14.36.09 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 14 Jun 2019 14:36:10 -0700 (PDT) From: Vitaly Kuznetsov To: Dmitry Safonov , Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Prasanna Panchamukhi , Andy Lutomirski , Borislav Petkov , Cathy Avery , Haiyang Zhang , "H. Peter Anvin" , Ingo Molnar , "K. Y. Srinivasan" , "Michael Kelley \(EOSG\)" , Mohammed Gamal , Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Roman Kagan , Sasha Levin , Stephen Hemminger , Thomas Gleixner , devel@linuxdriverproject.org, kvm@vger.kernel.org, linux-hyperv@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH] x86/hyperv: Disable preemption while setting reenlightenment vector In-Reply-To: References: <20190611212003.26382-1-dima@arista.com> <8736kff6q3.fsf@vitty.brq.redhat.com> <20190614082807.GV3436@hirez.programming.kicks-ass.net> <877e9o7a4e.fsf@vitty.brq.redhat.com> Date: Fri, 14 Jun 2019 23:36:09 +0200 Message-ID: <87sgsb6e9i.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Dmitry Safonov writes: > On 6/14/19 11:08 AM, Vitaly Kuznetsov wrote: >> Peter Zijlstra writes: >> >>> @@ -182,7 +182,7 @@ void set_hv_tscchange_cb(void (*cb)(void)) >>> struct hv_reenlightenment_control re_ctrl = { >>> .vector = HYPERV_REENLIGHTENMENT_VECTOR, >>> .enabled = 1, >>> - .target_vp = hv_vp_index[smp_processor_id()] >>> + .target_vp = hv_vp_index[raw_smp_processor_id()] >>> }; >>> struct hv_tsc_emulation_control emu_ctrl = {.enabled = 1}; >>> >> >> Yes, this should do, thanks! I'd also suggest to leave a comment like >> /* >> * This function can get preemted and migrate to a different CPU >> * but this doesn't matter. We just need to assign >> * reenlightenment notification to some online CPU. In case this >> * CPU goes offline, hv_cpu_die() will re-assign it to some >> * other online CPU. >> */ > > What if the cpu goes down just before wrmsrl()? > I mean, hv_cpu_die() will reassign another cpu, but this thread will be > resumed on some other cpu and will write cpu number which is at that > moment already down? > Right you are, we need to guarantee wrmsr() happens before the CPU gets a chance to go offline: we don't save the cpu number anywhere, we just read it with rdmsr() in hv_cpu_die(). > > And I presume it's guaranteed that during hv_cpu_die() no other cpu may > go down: > : new_cpu = cpumask_any_but(cpu_online_mask, cpu); > : re_ctrl.target_vp = hv_vp_index[new_cpu]; > : wrmsrl(HV_X64_MSR_REENLIGHTENMENT_CONTROL, *((u64 *)&re_ctrl)); I *think* I got convinced that CPUs don't go offline simultaneously when I was writing this. -- Vitaly