From nobody Sat Nov 15 17:05:55 2025 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass(p=quarantine dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1749666410; cv=none; d=zohomail.com; s=zohoarc; b=TLWsKy7KNXmUm8l4mtnKRzMooDUqsdYQhkk3VSLBgTaWBDWzCFlWpOSJ4MQeDVY31TaJwooD26rV6lerPoKzI9dy7fFF8BAmQTBn5JR7zo0DrHdD7RR2t7QwS4b8qOAUAdyBeT0Y/thHvyvrSrbM69SCkhKAuuw9N+rpZNz1pj8= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1749666410; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:Subject:To:To:Message-Id:Reply-To; bh=xkb+GWy3WwV0UX+pp8/jWU5Gi0bbhpy85QXCop36z+U=; b=L3+blReChdjYQTYtra/oY4R9l3F26aS9gWTfdE/w55fBwPWN4Y8L3NfGHt60Waab5ruXJ62IXWkskZXO+VHl3H1035xZP4CB6McX7OdbSgLTZWSRlayeeaby5KCBNRMAGKh82pztiBOen/YGiFhsOJH7nOXizdI+ldAoTsTohWk= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass header.from= (p=quarantine dis=none) Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1749666410912480.64356414189183; Wed, 11 Jun 2025 11:26:50 -0700 (PDT) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uPQ9l-0001Vy-A8; Wed, 11 Jun 2025 14:26:37 -0400 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 1uPQ9f-0001Qd-CG for qemu-devel@nongnu.org; Wed, 11 Jun 2025 14:26:31 -0400 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 1uPQ9G-0001GR-TQ for qemu-devel@nongnu.org; Wed, 11 Jun 2025 14:26:11 -0400 Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-281-OKcJr-I9OceoHkUS9DJXKw-1; Wed, 11 Jun 2025 14:26:03 -0400 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id BFFB6180028C; Wed, 11 Jun 2025 18:25:59 +0000 (UTC) Received: from localhost (unknown [10.2.16.122]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id A1A9019560A3; Wed, 11 Jun 2025 18:25:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1749666365; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xkb+GWy3WwV0UX+pp8/jWU5Gi0bbhpy85QXCop36z+U=; b=iT3kqWgzWJsl7SF6wm70zcIO8jgDpjXB6w25i3URZnUqXDoaQSshAdnEVCECQ3BYhDW9nl NmMEsvNn4VYxb4tnhvIgZR5E2phzhFqQPph0DduyjgRLRPm6W3NcXLUYlqsy0hIQhrUjcc MqRDkZLqnODfMw6oJqdiLz5Poievik0= X-MC-Unique: OKcJr-I9OceoHkUS9DJXKw-1 X-Mimecast-MFC-AGG-ID: OKcJr-I9OceoHkUS9DJXKw_1749666360 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: qemu-ppc@nongnu.org, Daniel Henrique Barboza , qemu-block@nongnu.org, Jesper Devantier , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , Peter Maydell , =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= , Harsh Prateek Bora , Troy Lee , Paolo Bonzini , Hanna Reitz , qemu-s390x@nongnu.org, Halil Pasic , Kevin Wolf , "Michael S. Tsirkin" , qemu-trivial@nongnu.org, Dmitry Fleytman , Jason Wang , Keith Busch , Nicholas Piggin , =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20Barrat?= , Fam Zheng , Sven Schnelle , Stefan Hajnoczi , Joel Stanley , Gerd Hoffmann , "Edgar E. Iglesias" , qemu-arm@nongnu.org, Hannes Reinecke , Klaus Jensen , Jeuk Kim , Andrew Jeffery , Alistair Francis , Thomas Huth , Michael Tokarev , Laurent Vivier , Rob Herring , Steven Lee , Jamin Lin , Christian Borntraeger , =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Subject: [PULL 02/31] hw/virtio/virtio: avoid cost of -ftrivial-auto-var-init in hot path Date: Wed, 11 Jun 2025 14:25:04 -0400 Message-ID: <20250611182533.200590-3-stefanha@redhat.com> In-Reply-To: <20250611182533.200590-1-stefanha@redhat.com> References: <20250611182533.200590-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1749666411927116600 Since commit 7ff9ff039380 ("meson: mitigate against use of uninitialize stack for exploits") the -ftrivial-auto-var-init=3Dzero compiler option is used to zero local variables. While this reduces security risks associated with uninitialized stack data, it introduced a measurable bottleneck in the virtqueue_split_pop() and virtqueue_packed_pop() functions. These virtqueue functions are in the hot path. They are called for each element (request) that is popped from a VIRTIO device's virtqueue. Using __attribute__((uninitialized)) on large stack variables in these functions improves fio randread bs=3D4k iodepth=3D64 performance from 304k to 332k IOPS (+9%). This issue was found using perf-top(1). virtqueue_split_pop() was one of the top CPU consumers and the "annotate" feature showed that the memory zeroing instructions at the beginning of the functions were hot. Fixes: 7ff9ff039380 ("meson: mitigate against use of uninitialize stack for= exploits") Cc: Daniel P. Berrang=C3=A9 Signed-off-by: Stefan Hajnoczi Reviewed-by: Stefan Hajnoczi Message-id: 20250610123709.835102-3-berrange@redhat.com Signed-off-by: Stefan Hajnoczi --- hw/virtio/virtio.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index 5534251e01..82a285a31d 100644 --- a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -1689,8 +1689,8 @@ static void *virtqueue_split_pop(VirtQueue *vq, size_= t sz) VirtIODevice *vdev =3D vq->vdev; VirtQueueElement *elem =3D NULL; unsigned out_num, in_num, elem_entries; - hwaddr addr[VIRTQUEUE_MAX_SIZE]; - struct iovec iov[VIRTQUEUE_MAX_SIZE]; + hwaddr QEMU_UNINITIALIZED addr[VIRTQUEUE_MAX_SIZE]; + struct iovec QEMU_UNINITIALIZED iov[VIRTQUEUE_MAX_SIZE]; VRingDesc desc; int rc; =20 @@ -1836,8 +1836,8 @@ static void *virtqueue_packed_pop(VirtQueue *vq, size= _t sz) VirtIODevice *vdev =3D vq->vdev; VirtQueueElement *elem =3D NULL; unsigned out_num, in_num, elem_entries; - hwaddr addr[VIRTQUEUE_MAX_SIZE]; - struct iovec iov[VIRTQUEUE_MAX_SIZE]; + hwaddr QEMU_UNINITIALIZED addr[VIRTQUEUE_MAX_SIZE]; + struct iovec QEMU_UNINITIALIZED iov[VIRTQUEUE_MAX_SIZE]; VRingPackedDesc desc; uint16_t id; int rc; --=20 2.49.0