From patchwork Fri Jan 20 01:11:16 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marcelo Tosatti X-Patchwork-Id: 13109141 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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id C150AC38159 for ; Fri, 20 Jan 2023 04:51:15 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pIjMB-0005i1-Av; Thu, 19 Jan 2023 23:50:27 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pIjM5-0005gg-Ba for qemu-devel@nongnu.org; Thu, 19 Jan 2023 23:50:23 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pIjM0-0005WH-9q for qemu-devel@nongnu.org; Thu, 19 Jan 2023 23:50:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674190215; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc; bh=Ja5jRaAjvA6A1qFpRyfbC8gO+Uf0HTRd1uhGwFrvQrA=; b=Ix+C+wyuqzilNuFGvQVedBvq0LP1u0dAP8Qo6GLhto51srfMm5cZ2wDA++Rvbww+5hVgmp 13W6Ozn0RSVB35CtazJiOhQIOdqR6Xjy1FR8k+KhzGEmJImmljjRiXFM1e//IdMQ8p0GO2 deKzUHPKES3YUPXA6vIqzJw6AoNz47o= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-297-IlHSVlbQP0ecRt23RKQ8VQ-1; Thu, 19 Jan 2023 23:48:50 -0500 X-MC-Unique: IlHSVlbQP0ecRt23RKQ8VQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 131BE85CBE0; Fri, 20 Jan 2023 04:48:50 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DC7EE40C2064; Fri, 20 Jan 2023 04:48:49 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id ED2F340517E51; Thu, 19 Jan 2023 22:15:17 -0300 (-03) Message-ID: <20230120011116.134437211@redhat.com> User-Agent: quilt/0.67 Date: Thu, 19 Jan 2023 22:11:16 -0300 From: Marcelo Tosatti To: qemu-devel@nongnu.org Cc: Paolo Bonzini , kvm@vger.kernel.org Subject: [PATCH 0/2] read kvmclock from guest memory if !correct_tsc_shift X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Received-SPF: pass client-ip=170.10.129.124; envelope-from=mtosatti@redhat.com; helo=us-smtp-delivery-124.mimecast.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, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, 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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Before kernel commit 78db6a5037965429c04d708281f35a6e5562d31b, kvm_guest_time_update() would use vcpu->virtual_tsc_khz to calculate tsc_shift value in the vcpus pvclock structure written to guest memory. For those kernels, if vcpu->virtual_tsc_khz != tsc_khz (which can be the case when guest state is restored via migration, or if tsc-khz option is passed to QEMU), and TSC scaling is not enabled (which happens if the difference between the frequency requested via KVM_SET_TSC_KHZ and the host TSC KHZ is smaller than 250ppm), then there can be a difference between what KVM_GET_CLOCK would return and what the guest reads as kvmclock value. The effect is that the guest sees a jump in kvmclock value (either forwards or backwards) in such case. To fix incoming migration from pre-78db6a5037965 hosts, read kvmclock value from guest memory. Unless the KVM_CLOCK_CORRECT_TSC_SHIFT bit indicates that the value retrieved by KVM_GET_CLOCK on the source is safe to be used.