From mboxrd@z Thu Jan 1 00:00:00 1970 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 F0D9FC3DA4A for ; Sun, 11 Aug 2024 17:21:31 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sdCFB-0005GL-2F; Sun, 11 Aug 2024 13:20:37 -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 1sdCF9-0005Fl-SU for qemu-devel@nongnu.org; Sun, 11 Aug 2024 13:20:36 -0400 Received: from mail-pl1-x62c.google.com ([2607:f8b0:4864:20::62c]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1sdCF8-0006EM-4C for qemu-devel@nongnu.org; Sun, 11 Aug 2024 13:20:35 -0400 Received: by mail-pl1-x62c.google.com with SMTP id d9443c01a7336-1ff4fa918afso21157485ad.1 for ; Sun, 11 Aug 2024 10:20:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1723396832; x=1724001632; darn=nongnu.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=wMbYqnbOieOsgh+FSColOA1P1rYTdb36qN+D9+ax72U=; b=C7q2vJfhBo80YWrmxNij9U25LS4mgw8OhoUb2d3cU3FN3dnZ7stXbkXWE16xOo5aoq JEJIfQwj2fHpUn1yhIzfX2Wpmeoq/XN4mJtCYS8Lr2TUwkC8YlI+n/Ey0FmOpqRKizCw bHIYRiGh8D1Up+4MWwM+87pzCFbyrXInsNEfk/JSQjhnqX5JlVWN5IYJUnQYNU9jEDjZ fohVtpK6nmteOWerIgNx16mfGMw25tQeLhOpTWv/HrplfQKirLsSlkmVVc/lqto0jx9U KwdQcktn2Xk1u/e7N0lvHts0KwbFsiVkvs4+GNGOqyKQz45RJS9/XQxQ+LDr0EPJi8hp DUaA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1723396832; x=1724001632; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=wMbYqnbOieOsgh+FSColOA1P1rYTdb36qN+D9+ax72U=; b=D30SQ36U8rpMnPN7pyNlw/9DKCJa8xgCMmz7rAYkEZ7tSB69v4ZLz5yDf4C+1QVe3C kc6GoEgrqnOXKXhjmlOJLXoUao/8usIAWXJRrpLqbOOBHu88/iPC3Angt2LhnF5M4VM0 RLl2dv+Y4qppmCjLeCGpAH+34zr4HygR07QIvO5zhrW7GJlhy8FyvUUWJKNbTzbQ6Q1C ECwponvaCUX/hKd/YWVlnT1axmuVcy7BmJLeAjfkDRA1+7lgJPaIWMduiCKhKxgiawDS K68Y1DoiDzqguXSKfPJd8mKX9pb0ixuUi6z/Gj4nLx/2z69mPI0nGbM7UunLFNY+Dybj DDrg== X-Forwarded-Encrypted: i=1; AJvYcCUGVRtZLfLNNd/LWN6Ixk67woj7upxCFNtyp0aTUlhKiKGAYFtJ7eXWeEsfog7nTwBoJKB0JyGiIlzDh09wlW962KWwoIY= X-Gm-Message-State: AOJu0Yz4fDL6qC3yKWaEhfYcHEXQXdq9jR6KJwkWXeBtw0cAN10otCRl ivdMMJ8zPIFQKUwRyEwxARKbwjlcBdRGNIkQ6HUsLX94ajBQCMMYWuGVPw== X-Google-Smtp-Source: AGHT+IEhHjdzem37eTLybDbdRgEw8CpMewLrxdkVWpNuEHgKXET3Q8SIQYee65Mm8EPyNYVxQE86sw== X-Received: by 2002:a17:902:e54e:b0:1f9:b9ed:e84e with SMTP id d9443c01a7336-200ae5f3127mr67032885ad.58.1723396832192; Sun, 11 Aug 2024 10:20:32 -0700 (PDT) Received: from valdaarhun.localnet ([223.233.81.106]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-200bba00771sm24776355ad.225.2024.08.11.10.20.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 11 Aug 2024 10:20:31 -0700 (PDT) From: Sahil To: Eugenio Perez Martin Cc: sgarzare@redhat.com, mst@redhat.com, qemu-devel@nongnu.org, Sahil Siddiq Subject: Re: [RFC v3 3/3] vhost: Allocate memory for packed vring Date: Sun, 11 Aug 2024 22:50:27 +0530 Message-ID: <23656540.6Emhk5qWAg@valdaarhun> In-Reply-To: References: <20240802112138.46831-1-sahilcdq@proton.me> <20240802112138.46831-4-sahilcdq@proton.me> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Received-SPF: pass client-ip=2607:f8b0:4864:20::62c; envelope-from=icegambit91@gmail.com; helo=mail-pl1-x62c.google.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 Hi, On Wednesday, August 7, 2024 9:52:10=E2=80=AFPM GMT+5:30 Eugenio Perez Mart= in wrote: > On Fri, Aug 2, 2024 at 1:22=E2=80=AFPM Sahil Siddiq wrote: > > [...] > > @@ -726,17 +738,30 @@ void vhost_svq_start(VhostShadowVirtqueue *svq, V= irtIODevice *vdev, > > svq->vring.num =3D virtio_queue_get_num(vdev, > > virtio_get_queue_index(vq)); > > svq->num_free =3D svq->vring.num; > >=20 > > - svq->vring.desc =3D mmap(NULL, vhost_svq_driver_area_size(svq), > > - PROT_READ | PROT_WRITE, MAP_SHARED | MAP_AN= ONYMOUS, > > - -1, 0); > > - desc_size =3D sizeof(vring_desc_t) * svq->vring.num; > > - svq->vring.avail =3D (void *)((char *)svq->vring.desc + desc_size); > > - svq->vring.used =3D mmap(NULL, vhost_svq_device_area_size(svq), > > - PROT_READ | PROT_WRITE, MAP_SHARED | MAP_AN= ONYMOUS, > > - -1, 0); > > - svq->desc_state =3D g_new0(SVQDescState, svq->vring.num); > > - svq->desc_next =3D g_new0(uint16_t, svq->vring.num); > > - for (unsigned i =3D 0; i < svq->vring.num - 1; i++) { > > + svq->is_packed =3D virtio_vdev_has_feature(svq->vdev, VIRTIO_F_RIN= G_PACKED); > > + > > + if (virtio_vdev_has_feature(svq->vdev, VIRTIO_F_RING_PACKED)) { > > + svq->vring_packed.vring.desc =3D mmap(NULL, vhost_svq_memory_p= acked(svq), > > + PROT_READ | PROT_WRITE, MAP_= SHARED | MAP_ANONYMOUS, > > + -1, 0); > > + desc_size =3D sizeof(struct vring_packed_desc) * svq->vring.nu= m; > > + svq->vring_packed.vring.driver =3D (void *)((char *)svq->vring= _packed.vring.desc + desc_size); > > + svq->vring_packed.vring.device =3D (void *)((char *)svq->vring= _packed.vring.driver + > > + sizeof(struct vring_packed_desc_e= vent)); > > This is a great start but it will be problematic when you start > mapping the areas to the vdpa device. The driver area should be read > only for the device, but it is placed in the same page as a RW one. > > More on this later. >=20 > > + } else { > > + svq->vring.desc =3D mmap(NULL, vhost_svq_driver_area_size(svq), > > + PROT_READ | PROT_WRITE, MAP_SHARED |MAP= _ANONYMOUS, > > + -1, 0); > > + desc_size =3D sizeof(vring_desc_t) * svq->vring.num; > > + svq->vring.avail =3D (void *)((char *)svq->vring.desc + desc_s= ize); > > + svq->vring.used =3D mmap(NULL, vhost_svq_device_area_size(svq), > > + PROT_READ | PROT_WRITE, MAP_SHARED |MAP= _ANONYMOUS, > > + -1, 0); > > + } >=20 > I think it will be beneficial to avoid "if (packed)" conditionals on > the exposed functions that give information about the memory maps. > These need to be replicated at > hw/virtio/vhost-vdpa.c:vhost_vdpa_svq_map_rings. >=20 > However, the current one depends on the driver area to live in the > same page as the descriptor area, so it is not suitable for this. I haven't really understood this. In split vqs the descriptor, driver and device areas are mapped to RW pages. In vhost_vdpa.c:vhost_vdpa_svq_map_rings, the regions are mapped with the appropriate "perm" field that sets the R/W permissions in the DMAMap object. Is this problematic for the split vq format because the avail ring = is anyway mapped to a RW page in "vhost_svq_start"? =46or packed vqs, the "Driver Event Suppression" data structure should be read-only for the device. Similar to split vqs, this is mapped to a RW page in "vhost_svq_start" but it is then mapped to a DMAMap object with read- only perms in "vhost_vdpa_svq_map_rings". I am a little confused about where the issue lies. Thanks, Sahil