From patchwork Fri Jun 26 07:22:29 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 11626639 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id A09F06C1 for ; Fri, 26 Jun 2020 07:23:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 88F072076E for ; Fri, 26 Jun 2020 07:23:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="O+xTlzBc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728078AbgFZHX0 (ORCPT ); Fri, 26 Jun 2020 03:23:26 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:43812 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727022AbgFZHX0 (ORCPT ); Fri, 26 Jun 2020 03:23:26 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1593156204; 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: in-reply-to:in-reply-to:references:references; bh=infcIEMl/Gu4WfpC7vb6GTLKifCdfLNGQXbx7ZFcrfg=; b=O+xTlzBcSqSY+mRxNlPDbKEunMqXdJIQOGg1CazK2nzUwjrInvYz9zUw4uZiZT2oy8X+BB icv1Cq8chO6XyJulTywVIQm40ebBAYhr8Al2K4Jlnls1hydYTOH1n9fW2Gddhk9pMMaGoQ bnE/5y7uIMfQaDVL+F2D6BiXxC2TARI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-97-30gyrpDANUyD9sflQgKWxQ-1; Fri, 26 Jun 2020 03:23:21 -0400 X-MC-Unique: 30gyrpDANUyD9sflQgKWxQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3107C18FE879; Fri, 26 Jun 2020 07:23:20 +0000 (UTC) Received: from t480s.redhat.com (ovpn-113-35.ams2.redhat.com [10.36.113.35]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5A2FD60C1D; Fri, 26 Jun 2020 07:23:18 +0000 (UTC) From: David Hildenbrand To: qemu-devel@nongnu.org Cc: kvm@vger.kernel.org, qemu-s390x@nongnu.org, Richard Henderson , Paolo Bonzini , "Dr . David Alan Gilbert" , Eduardo Habkost , "Michael S . Tsirkin" , David Hildenbrand Subject: [PATCH v5 02/21] exec: Introduce ram_block_discard_(disable|require)() Date: Fri, 26 Jun 2020 09:22:29 +0200 Message-Id: <20200626072248.78761-3-david@redhat.com> In-Reply-To: <20200626072248.78761-1-david@redhat.com> References: <20200626072248.78761-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org We want to replace qemu_balloon_inhibit() by something more generic. Especially, we want to make sure that technologies that really rely on RAM block discards to work reliably to run mutual exclusive with technologies that effectively break it. E.g., vfio will usually pin all guest memory, turning the virtio-balloon basically useless and make the VM consume more memory than reported via the balloon. While the balloon is special already (=> no guarantees, same behavior possible afer reboots and with huge pages), this will be different, especially, with virtio-mem. Let's implement a way such that we can make both types of technology run mutually exclusive. We'll convert existing balloon inhibitors in successive patches and add some new ones. Add the check to qemu_balloon_is_inhibited() for now. We might want to make virtio-balloon an acutal inhibitor in the future - however, that requires more thought to not break existing setups. Reviewed-by: Dr. David Alan Gilbert Cc: "Michael S. Tsirkin" Cc: Richard Henderson Cc: Paolo Bonzini Signed-off-by: David Hildenbrand --- balloon.c | 3 ++- exec.c | 52 +++++++++++++++++++++++++++++++++++++++++++ include/exec/memory.h | 41 ++++++++++++++++++++++++++++++++++ 3 files changed, 95 insertions(+), 1 deletion(-) diff --git a/balloon.c b/balloon.c index f104b42961..5fff79523a 100644 --- a/balloon.c +++ b/balloon.c @@ -40,7 +40,8 @@ static int balloon_inhibit_count; bool qemu_balloon_is_inhibited(void) { - return atomic_read(&balloon_inhibit_count) > 0; + return atomic_read(&balloon_inhibit_count) > 0 || + ram_block_discard_is_disabled(); } void qemu_balloon_inhibit(bool state) diff --git a/exec.c b/exec.c index d6712fba7e..b15187d9ab 100644 --- a/exec.c +++ b/exec.c @@ -4063,4 +4063,56 @@ void mtree_print_dispatch(AddressSpaceDispatch *d, MemoryRegion *root) } } +/* + * If positive, discarding RAM is disabled. If negative, discarding RAM is + * required to work and cannot be disabled. + */ +static int ram_block_discard_disabled; + +int ram_block_discard_disable(bool state) +{ + int old; + + if (!state) { + atomic_dec(&ram_block_discard_disabled); + return 0; + } + + do { + old = atomic_read(&ram_block_discard_disabled); + if (old < 0) { + return -EBUSY; + } + } while (atomic_cmpxchg(&ram_block_discard_disabled, old, old + 1) != old); + return 0; +} + +int ram_block_discard_require(bool state) +{ + int old; + + if (!state) { + atomic_inc(&ram_block_discard_disabled); + return 0; + } + + do { + old = atomic_read(&ram_block_discard_disabled); + if (old > 0) { + return -EBUSY; + } + } while (atomic_cmpxchg(&ram_block_discard_disabled, old, old - 1) != old); + return 0; +} + +bool ram_block_discard_is_disabled(void) +{ + return atomic_read(&ram_block_discard_disabled) > 0; +} + +bool ram_block_discard_is_required(void) +{ + return atomic_read(&ram_block_discard_disabled) < 0; +} + #endif diff --git a/include/exec/memory.h b/include/exec/memory.h index 7207025bd4..38ec38b9a8 100644 --- a/include/exec/memory.h +++ b/include/exec/memory.h @@ -2472,6 +2472,47 @@ static inline MemOp devend_memop(enum device_endian end) } #endif +/* + * Inhibit technologies that require discarding of pages in RAM blocks, e.g., + * to manage the actual amount of memory consumed by the VM (then, the memory + * provided by RAM blocks might be bigger than the desired memory consumption). + * This *must* be set if: + * - Discarding parts of a RAM blocks does not result in the change being + * reflected in the VM and the pages getting freed. + * - All memory in RAM blocks is pinned or duplicated, invaldiating any previous + * discards blindly. + * - Discarding parts of a RAM blocks will result in integrity issues (e.g., + * encrypted VMs). + * Technologies that only temporarily pin the current working set of a + * driver are fine, because we don't expect such pages to be discarded + * (esp. based on guest action like balloon inflation). + * + * This is *not* to be used to protect from concurrent discards (esp., + * postcopy). + * + * Returns 0 if successful. Returns -EBUSY if a technology that relies on + * discards to work reliably is active. + */ +int ram_block_discard_disable(bool state); + +/* + * Inhibit technologies that disable discarding of pages in RAM blocks. + * + * Returns 0 if successful. Returns -EBUSY if discards are already set to + * broken. + */ +int ram_block_discard_require(bool state); + +/* + * Test if discarding of memory in ram blocks is disabled. + */ +bool ram_block_discard_is_disabled(void); + +/* + * Test if discarding of memory in ram blocks is required to work reliably. + */ +bool ram_block_discard_is_required(void); + #endif #endif