From patchwork Sat Oct 22 15:48:21 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Emanuele Giuseppe Esposito X-Patchwork-Id: 13015999 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 F3D20C04A95 for ; Sat, 22 Oct 2022 15:48:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229945AbiJVPsl (ORCPT ); Sat, 22 Oct 2022 11:48:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34516 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229886AbiJVPsd (ORCPT ); Sat, 22 Oct 2022 11:48:33 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D030EAE4F for ; Sat, 22 Oct 2022 08:48:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1666453708; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=OPS/W9EriOxXRzwj2N2ZjlWHOy5hj1Gjuemf2SY5Ke0=; b=EAFK8OEM90I7IhyDUen80GO9ZRc1GwsVrvNjFUYeZV7N9CkJzzZywFzmU9Ac/GO9bdclg4 Z1vJjPdyQ6n4fOr2u6b13qeDqFrVeP1cLzOr6lXr+s0YW7G4NudhOrnV6PWtDgjAZbUdGQ UB7+u7lPr+Dth32AHBX+bW4zlg2DBSQ= 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-54-HeEXPnPlOyOnOd3OwjkhyQ-1; Sat, 22 Oct 2022 11:48:26 -0400 X-MC-Unique: HeEXPnPlOyOnOd3OwjkhyQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7FAD4811E7A; Sat, 22 Oct 2022 15:48:26 +0000 (UTC) Received: from virtlab701.virt.lab.eng.bos.redhat.com (virtlab701.virt.lab.eng.bos.redhat.com [10.19.152.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id 392F840C6EC2; Sat, 22 Oct 2022 15:48:25 +0000 (UTC) From: Emanuele Giuseppe Esposito To: qemu-devel@nongnu.org Cc: Paolo Bonzini , Maxim Levitsky , "Michael S. Tsirkin" , Cornelia Huck , David Hildenbrand , kvm@vger.kernel.org, Emanuele Giuseppe Esposito Subject: [PATCH 0/2] KVM: stop all vcpus before modifying memslots Date: Sat, 22 Oct 2022 11:48:21 -0400 Message-Id: <20221022154823.1823193-1-eesposit@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org QEMU needs to perform memslots operations like merging and splitting, and each operation requires more than a single ioctl. Therefore if a vcpu is concurrently reading the same memslots, it could end up reading something that was temporarly deleted. For example, merging two memslots into one would imply: DELETE(m1) DELETE(m2) CREATE(m1+m2) And a vcpu could attempt to read m2 right after it is deleted, but before the new one is created. To solve this problem, use the newly introduced kvm API: KVM_KICK_ALL_RUNNING_VCPUS and KVM_RESUME_ALL_KICKED_VCPUS. This new API allows the userspace to respectively stop and resume all running vcpus. A "running" vcpu is a vcpu that is executing the KVM_RUN ioctl. While KVM already handles the case of KVM_RUN being called after KVM_KICK_ALL_RUNNING_VCPUS is invoked but before KVM_RESUME_ALL_KICKED_VCPUS by simply returning immediately, QEMU also avoids that using the event API. This is the simplest solution, pausing all vcpus in the kvm side, so that: - QEMU just needs to call the new API before making memslots changes, keeping modifications to the minimum - dirty page updates are also performed when vcpus are blocked, so there is no time window between the dirty page ioctl and memslots modifications, since vcpus are all stopped. - no need to modify the existing memslots API This series requires the KVM serie "KVM: API to block and resume all running vcpus in a vm". Emanuele Giuseppe Esposito (2): linux-headers/linux/kvm.h: introduce kvm_userspace_memory_region_list ioctl accel/kvm: introduce begin/commit listener callbacks accel/kvm/kvm-all.c | 50 +++++++++++++++++++++++++++++++++++++++ linux-headers/linux/kvm.h | 3 +++ 2 files changed, 53 insertions(+)