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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 20F09C433ED for ; Tue, 6 Apr 2021 20:26:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D3B79613D3 for ; Tue, 6 Apr 2021 20:26:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235205AbhDFU0w (ORCPT ); Tue, 6 Apr 2021 16:26:52 -0400 Received: from isrv.corpit.ru ([86.62.121.231]:35871 "EHLO isrv.corpit.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231339AbhDFU0v (ORCPT ); Tue, 6 Apr 2021 16:26:51 -0400 X-Greylist: delayed 539 seconds by postgrey-1.27 at vger.kernel.org; Tue, 06 Apr 2021 16:26:51 EDT Received: from tsrv.corpit.ru (tsrv.tls.msk.ru [192.168.177.2]) by isrv.corpit.ru (Postfix) with ESMTP id 24487402A3; Tue, 6 Apr 2021 23:17:42 +0300 (MSK) Received: from [192.168.177.130] (mjt.wg.tls.msk.ru [192.168.177.130]) by tsrv.corpit.ru (Postfix) with ESMTP id 0529521E; Tue, 6 Apr 2021 23:17:41 +0300 (MSK) To: kvm@vger.kernel.org, qemu-devel@nongnu.org, Thomas Gleixner Cc: Paolo Bonzini From: Michael Tokarev Subject: Commit "x86/kvm: Move context tracking where it belongs" broke guest time accounting Message-ID: <36088364-0b3d-d492-0aa4-59ea8f1d1632@msgid.tls.msk.ru> Date: Tue, 6 Apr 2021 23:17:41 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Hi! It looks like this commit: commit 87fa7f3e98a1310ef1ac1900e7ee7f9610a038bc Author: Thomas Gleixner Date: Wed Jul 8 21:51:54 2020 +0200 x86/kvm: Move context tracking where it belongs Context tracking for KVM happens way too early in the vcpu_run() code. Anything after guest_enter_irqoff() and before guest_exit_irqoff() cannot use RCU and should also be not instrumented. The current way of doing this covers way too much code. Move it closer to the actual vmenter/exit code. broke kvm guest cpu time accounting - after this commit, when running qemu-system-x86_64 -enable-kvm, the guest time (in /proc/stat and elsewhere) is always 0. I dunno why it happened, but it happened, and all kernels after 5.9 are affected by this. This commit is found in a (painful) git bisect between kernel 5.8 and 5.10. Thanks, /mjt