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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 A833EC433FE for ; Fri, 4 Dec 2020 20:52:50 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0C86B22CE3 for ; Fri, 4 Dec 2020 20:52:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0C86B22CE3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=yadro.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:39010 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1klI4O-0002OB-EZ for qemu-devel@archiver.kernel.org; Fri, 04 Dec 2020 15:52:48 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:32868) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1klFcA-0007G7-Fl; Fri, 04 Dec 2020 13:15:40 -0500 Received: from mta-02.yadro.com ([89.207.88.252]:47738 helo=mta-01.yadro.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1klFc0-0003QE-4K; Fri, 04 Dec 2020 13:15:22 -0500 Received: from localhost (unknown [127.0.0.1]) by mta-01.yadro.com (Postfix) with ESMTP id 62A68413F1; Fri, 4 Dec 2020 18:15:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=yadro.com; h= in-reply-to:content-disposition:content-type:content-type :mime-version:references:message-id:subject:subject:from:from :date:date:received:received:received; s=mta-01; t=1607105714; x=1608920115; bh=YVGyE8TlAzd8/jfGdj6zfujGWcv13xuBM4HkZSrsiqI=; b= l2xUQh8wSKibMxU9ggiQlfsn0T/pwPVDHwDTdqA/38SvYxxnhYEVlKOFqyc8U7pS dC/+VcHkOkjMmQ20AWJBAZd0IPOwcXfaA/TME+K6JOpwanKoAjtvLjlDPaocicjY Jhh/EwoXsLlGZNX/WUtfHdIO0mGtvUdGeIaSdfOSjOM= X-Virus-Scanned: amavisd-new at yadro.com Received: from mta-01.yadro.com ([127.0.0.1]) by localhost (mta-01.yadro.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id i8FiuNgjj_3F; Fri, 4 Dec 2020 21:15:14 +0300 (MSK) Received: from T-EXCH-03.corp.yadro.com (t-exch-03.corp.yadro.com [172.17.100.103]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by mta-01.yadro.com (Postfix) with ESMTPS id 79A5A4139B; Fri, 4 Dec 2020 21:15:13 +0300 (MSK) Received: from localhost (172.17.204.212) by T-EXCH-03.corp.yadro.com (172.17.100.103) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P384) id 15.1.669.32; Fri, 4 Dec 2020 21:15:13 +0300 Date: Fri, 4 Dec 2020 21:15:36 +0300 From: Roman Bolshakov To: Peter Collingbourne Subject: Re: [PATCH v3 08/10] arm/hvf: Add a WFI handler Message-ID: <20201204181536.GL86904@SPB-NB-133.local> References: <20201202190408.2041-1-agraf@csgraf.de> <20201202190408.2041-9-agraf@csgraf.de> <20201203103949.GC7201@SPB-NB-133.local> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-Originating-IP: [172.17.204.212] X-ClientProxiedBy: T-EXCH-01.corp.yadro.com (172.17.10.101) To T-EXCH-03.corp.yadro.com (172.17.100.103) Received-SPF: pass client-ip=89.207.88.252; envelope-from=r.bolshakov@yadro.com; helo=mta-01.yadro.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Eduardo Habkost , Richard Henderson , qemu-devel , Cameron Esfahani , Alexander Graf , qemu-arm , Frank Yang , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Dec 03, 2020 at 10:18:14AM -0800, Peter Collingbourne wrote: > On Thu, Dec 3, 2020 at 2:39 AM Roman Bolshakov wrote: > > > > On Wed, Dec 02, 2020 at 08:04:06PM +0100, Alexander Graf wrote: > > > From: Peter Collingbourne > > > > > > Sleep on WFI until the VTIMER is due but allow ourselves to be woken > > > up on IPI. > > > > > > Signed-off-by: Peter Collingbourne > > > [agraf: Remove unused 'set' variable, always advance PC on WFX trap] > > > Signed-off-by: Alexander Graf > > > --- > > > +static void hvf_wait_for_ipi(CPUState *cpu, struct timespec *ts) > > > +{ > > > + /* > > > + * Use pselect to sleep so that other threads can IPI us while we're > > > + * sleeping. > > > + */ > > > + qatomic_mb_set(&cpu->thread_kicked, false); > > > + qemu_mutex_unlock_iothread(); > > > > I raised a concern earlier, but I don't for sure if a kick could be lost > > right here. On x86 it could be lost. > > If the signal is sent right before the pselect() it will be blocked > i.e. left pending. With the pselect() we get an atomic unblock of > SIG_IPI at the same time as we begin sleeping, which means that we > will receive the signal and leave the pselect() immediately. > > I think at some point macOS had an incorrect implementation of > pselect() where the signal mask was non-atomically set in userspace > which could lead to the signal being missed but I checked the latest > XNU sources and it looks like the pselect() implementation has been > moved to the kernel. > Yeah, you're right here. > > > + pselect(0, 0, 0, 0, ts, &cpu->hvf->unblock_ipi_mask); > > > + qemu_mutex_lock_iothread(); > > > +} > > > + > > > int hvf_vcpu_exec(CPUState *cpu) > > > { > > > ARMCPU *arm_cpu = ARM_CPU(cpu); > > > @@ -579,6 +594,46 @@ int hvf_vcpu_exec(CPUState *cpu) > > > } > > > case EC_WFX_TRAP: > > > advance_pc = true; > > > + if (!(syndrome & WFX_IS_WFE) && !(cpu->interrupt_request & > > > + (CPU_INTERRUPT_HARD | CPU_INTERRUPT_FIQ))) { > > > + > > > + uint64_t ctl; > > > + r = hv_vcpu_get_sys_reg(cpu->hvf->fd, HV_SYS_REG_CNTV_CTL_EL0, > > > + &ctl); > > > + assert_hvf_ok(r); > > > + > > > + if (!(ctl & 1) || (ctl & 2)) { > > > + /* Timer disabled or masked, just wait for an IPI. */ > > > + hvf_wait_for_ipi(cpu, NULL); > > > + break; > > > + } > > > + > > > + uint64_t cval; > > > + r = hv_vcpu_get_sys_reg(cpu->hvf->fd, HV_SYS_REG_CNTV_CVAL_EL0, > > > + &cval); > > > + assert_hvf_ok(r); > > > + > > > + int64_t ticks_to_sleep = cval - mach_absolute_time(); > > > > > > Apple reference recommends to use [1]: > > > > clock_gettime_nsec_np(CLOCK_UPTIME_RAW) > > > > It, internally in Libc, invokes mach_absolute_time() [2]. > > > > 1. https://developer.apple.com/documentation/kernel/1462446-mach_absolute_time > > 2. https://opensource.apple.com/source/Libc/Libc-1158.1.2/gen/clock_gettime.c.auto.html > > I think that recommendation is because most people want to deal with > seconds, not ticks. In our case we specifically want ticks because > we're comparing against a ticks value from the guest, so I don't see > the benefit of converting from ticks to seconds and back again. > Thanks for the clarifications, Peter. Regards, Roman