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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7E453C433EF for ; Fri, 17 Dec 2021 14:51:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237576AbhLQOvW (ORCPT ); Fri, 17 Dec 2021 09:51:22 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47678 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237552AbhLQOvW (ORCPT ); Fri, 17 Dec 2021 09:51:22 -0500 Received: from mail-wr1-x42f.google.com (mail-wr1-x42f.google.com [IPv6:2a00:1450:4864:20::42f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B4F0EC061574; Fri, 17 Dec 2021 06:51:21 -0800 (PST) Received: by mail-wr1-x42f.google.com with SMTP id i22so4467992wrb.13; Fri, 17 Dec 2021 06:51:21 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=sender:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=mnebuQGqRVJGN2DsZ9eHW1+KpUOSevBvrqS9hjun5HA=; b=ZjTNEfc6zK60plX/MF6o4daNldO/KbO+PvVYiMB+SaIqCvXZ7TyjN1ZuSFyxaBe0ZG rGdblOWXBUAlA4vJY9vIHZilZZdkP6G4OQvKA9HBbK+/POhbux6DZV+Xn9aZh+7D25gw YsI/wAiMr6cVQl5HhqR6J96714rjxCTwE0QG5DjZLonH69P1U/gTHclxEM49QmKKeu0U iqIv5Da3muuv/zmHQ0QMecdPqFGvv/ZIN4VGGVgh4WJstnMFjj3ogLdiDmqH16wu06NS 1QGuE4q9HejJCgL+FS/XIgsS0/2noHo3BdkBa/ZZu60rQrVxcpJul8pShfrUNGvuJ1S5 G8AQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:sender:message-id:date:mime-version:user-agent :subject:content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=mnebuQGqRVJGN2DsZ9eHW1+KpUOSevBvrqS9hjun5HA=; b=c+XghLGBsK/E0hVZJzvvWocizrRT4R0FWyW3fL5bBAgRMHegTqHtbsfaPvyqmE1fTF oVVGRwQBtdsh0pmZCSLW9Qghf/cAjdixhLFreC/YSHZU5GAhq2VLaS5AFcmoIwA534xk 4gE5+mgzGN77okMlZy2V8NRltxcAzD6xGi6M1zcl/d+Fyv6onWN6HiH3ThaG6VBsAbNI pgl/hUi7tPZlffyiNew0RBu3o5dz6RHQ+vc8pyV/r4lGzL/w6zKsryFLn3UYblTjedzU 5oH8jDgqGq4dKo4p9E7s/JsnWpkzOekfd16Z+0FsPJGXZOP2RzfsYT9okVUGAEzXe8V8 11rQ== X-Gm-Message-State: AOAM532Axy0IRU8KpVp28j0JW13sJ3lW4gejlnEGzXKyB++9ff2BHz1Y OmSnhQs9DIt9yLM8kzqnif4= X-Google-Smtp-Source: ABdhPJxEcEhIcUYsKzOAN6IqL39vwVjInx/LM/aFur/79bTs0fYRfHfINZo6PTnpTWAnMXXZlNDMJg== X-Received: by 2002:adf:ca0f:: with SMTP id o15mr2828708wrh.457.1639752680231; Fri, 17 Dec 2021 06:51:20 -0800 (PST) Received: from ?IPV6:2001:b07:6468:f312:48f9:bea:a04c:3dfe? ([2001:b07:6468:f312:48f9:bea:a04c:3dfe]) by smtp.googlemail.com with ESMTPSA id a10sm12136566wmq.27.2021.12.17.06.51.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Dec 2021 06:51:19 -0800 (PST) Sender: Paolo Bonzini Message-ID: Date: Fri, 17 Dec 2021 15:51:14 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: Possible nohz-full/RCU issue in arm64 KVM Content-Language: en-US To: Mark Rutland , Nicolas Saenz Julienne Cc: paulmck , maz , frederic , linux-kernel , rcu , Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel , "kvm-riscv@lists.infradead.org" , Anup Patel References: From: Paolo Bonzini In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/17/21 14:21, Mark Rutland wrote: > I'm not immediately sure what we*should* do here. What does x86 do for an IRQ > taken from a guest mode? I couldn't spot any handling of that case, but I'm not > familiar enough with the x86 exception model to know if I'm looking in the > right place. ARM is missing something like commit 160457140187 ("KVM: x86: Defer vtime accounting 'til after IRQ handling", 2021-05-05). With that change, it would be possible to move guest_exit() in the irq-disabled region without breaking time accounting. RISC-V has the same issue and it would be fixed in the same way, so let's Cc Anup too. Paolo