From patchwork Fri Sep 9 10:44:57 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: 12971488 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 CCEE2ECAAD3 for ; Fri, 9 Sep 2022 10:45:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231161AbiIIKpV (ORCPT ); Fri, 9 Sep 2022 06:45:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39926 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230468AbiIIKpR (ORCPT ); Fri, 9 Sep 2022 06:45:17 -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 DEBDB4BA7E for ; Fri, 9 Sep 2022 03:45:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1662720313; 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=GS6z751jOS17P5KjjAKA6XFU5o/FNq7ECC/sWEiv1wc=; b=e5jg4GsEbWZyjBtV1RtUCxlb+FhUYxqPo6iW2oRE5HDC5VrDgT8FtGxcUaaUTWR3dMUrIh B97D+KyGEeGnT8nlUmu1ZK2yiZUdsbzmraFNMlKQJ/wYmyHqYet/qnZlyNFDuHgsUlJdhC BJxWEmJ35r8R7zTCo432eaTZhJncmQw= 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-582-V6wIM2X6MCqAcYvkPXZmGw-1; Fri, 09 Sep 2022 06:45:09 -0400 X-MC-Unique: V6wIM2X6MCqAcYvkPXZmGw-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 386D4101A56D; Fri, 9 Sep 2022 10:45:09 +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 1907840D2830; Fri, 9 Sep 2022 10:45:08 +0000 (UTC) From: Emanuele Giuseppe Esposito To: kvm@vger.kernel.org Cc: Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , David Hildenbrand , Maxim Levitsky , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org, Emanuele Giuseppe Esposito Subject: [RFC PATCH 0/9] kvm: implement atomic memslot updates Date: Fri, 9 Sep 2022 06:44:57 -0400 Message-Id: <20220909104506.738478-1-eesposit@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org KVM is currently capable of receiving a single memslot update through the KVM_SET_USER_MEMORY_REGION ioctl. The problem arises when we want to atomically perform multiple updates, so that readers of memslot active list avoid seeing incomplete states. For example, in RHBZ https://bugzilla.redhat.com/show_bug.cgi?id=1979276 we see how non atomic updates cause boot failure, because vcpus will se a partial update (old memslot delete, new one not yet created) and will crash. In this series we introduce KVM_SET_USER_MEMORY_REGION_LIST, a new ioctl that takes a kvm_userspace_memory_region_list, a list of memslot updates, and performs them atomically. "atomically" in KVM words just means "apply all modifications to the inactive memslot list, and then perform a single swap to replace the active list with the inactive". It is slightly more complicated that that, since DELETE and MOVE operations require 2 swaps, but the main idea is the above. Patch 1-6 are just code movements, in preparation for the following patches. Patch 7 allows the invalid slot to be in both inactive and active memslot lists. Patch 8 allows searching for the existing memslot (old) in the inactive list, and not the active, allowing to perform multiple memslot updates without swapping. Patch 9 implements IOCTL logic. QEMU userspace logic in preparation for the IOCTL is here: https://patchew.org/QEMU/20220909081150.709060-1-eesposit@redhat.com/ "[RFC PATCH v2 0/3] accel/kvm: extend kvm memory listener to support" TODOs and ideas: - limit the size of the ioctl arguments. Right now it is unbounded - try to reduce the amount of swaps necessary? ie every DELETE/MOVE requires an additional swap - add selftests - add documentation Emanuele Giuseppe Esposito (9): kvm_main.c: move slot check in kvm_set_memory_region kvm.h: introduce KVM_SET_USER_MEMORY_REGION_LIST ioctl kvm_main.c: introduce kvm_internal_memory_region_list kvm_main.c: split logic in kvm_set_memslots kvm_main.c: split __kvm_set_memory_region logic in kvm_check_mem and kvm_prepare_batch kvm_main.c: simplify change-specific callbacks kvm_main.c: duplicate invalid memslot also in inactive list kvm_main.c: find memslots from the inactive memslot list kvm_main.c: handle atomic memslot update arch/x86/kvm/x86.c | 3 +- include/linux/kvm_host.h | 21 +- include/uapi/linux/kvm.h | 21 +- virt/kvm/kvm_main.c | 420 +++++++++++++++++++++++++++++++-------- 4 files changed, 377 insertions(+), 88 deletions(-) Signed-off-by: Sean Christopherson