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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4BE3EC7EE43 for ; Mon, 12 Jun 2023 21:53:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233166AbjFLVx1 (ORCPT ); Mon, 12 Jun 2023 17:53:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55860 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238286AbjFLVxJ (ORCPT ); Mon, 12 Jun 2023 17:53:09 -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 EDF8510D8 for ; Mon, 12 Jun 2023 14:52:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1686606735; 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=boA3uYLp9Lq3xOIcpkhvQI3DYCAEvrjZcD5trap1f04=; b=NLEcMe1SrKj9XrYo5BQRoT9292t4/G+/lTzLlFMV4WIzUOpOvx3vdRwP/dp/JadX+Djg1n DUfwXsH5gS4JP+/EtIDLJ9xmMS87cYXJyVKwoNqVd7daX99P7jQvXSUJNTiCoxvIRC4niB 8qTWG8QNHCZDDLhkx7aLPVIOxW+JRfc= Received: from mail-io1-f71.google.com (mail-io1-f71.google.com [209.85.166.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-612-fGHaZlZuOjiB6WyOz_7bhQ-1; Mon, 12 Jun 2023 17:52:13 -0400 X-MC-Unique: fGHaZlZuOjiB6WyOz_7bhQ-1 Received: by mail-io1-f71.google.com with SMTP id ca18e2360f4ac-77ac14e9bc5so585767139f.2 for ; Mon, 12 Jun 2023 14:52:13 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1686606733; x=1689198733; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=boA3uYLp9Lq3xOIcpkhvQI3DYCAEvrjZcD5trap1f04=; b=ibDlTNSPhnuV11+MPag4rCoZulUAT2ieIfcd6eKgQjagKkhjMuCsIDDX/sR3YKYyWg aolZ/oLj5pCtCFp0uhqDh/g4MLbI01ar/4NdUqA/QxngtpPqJD1FxOJ3UPK9uqm02UQY U0p8jRi+LhdHxkPqXeT78dfGruJKVOWmtu2m/XynPGHEArTIFBsNbudgUCoXOdbPo6F2 XYkBBLaI1H4eSHqDjwfq03/5v/tno0N2wCP4MwdDimF9FxfwP9i/u3N1gVtGUWwqFy7f 6zdyXHa8TL9YeP8BbsENXQfVE+ANcBxJG9ZOlbKWCmOyZ1giI49QUEmeqiHGQP52HSBC 63vA== X-Gm-Message-State: AC+VfDzT/ivoAFzqbiFrT/mBOqqKkCCH/YOAAFcThylnwOnCXgJydcn6 I2NXILaffesVir81MZ36m4uVOEIHtiO4a2wVCpy6lhRE0Hh+4U/MtO18/8EUgWYzofn+TgUuK2V UvGp98NqCBKrne4oJp2p8Xg== X-Received: by 2002:a6b:7b45:0:b0:77a:ec0c:5907 with SMTP id m5-20020a6b7b45000000b0077aec0c5907mr6931510iop.13.1686606733112; Mon, 12 Jun 2023 14:52:13 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ63rekNLLQDnyK8nJOL8AIQHD4qdXRPI2wqFuMCbJroFEC5NjXVpyDmFDmxaenIzEmd4Wxl3A== X-Received: by 2002:a6b:7b45:0:b0:77a:ec0c:5907 with SMTP id m5-20020a6b7b45000000b0077aec0c5907mr6931503iop.13.1686606732857; Mon, 12 Jun 2023 14:52:12 -0700 (PDT) Received: from redhat.com ([38.15.36.239]) by smtp.gmail.com with ESMTPSA id u15-20020a02cbcf000000b0040f9af9237asm160026jaq.41.2023.06.12.14.52.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Jun 2023 14:52:12 -0700 (PDT) Date: Mon, 12 Jun 2023 15:52:10 -0600 From: Alex Williamson To: Yi Liu Cc: jgg@nvidia.com, kevin.tian@intel.com, joro@8bytes.org, robin.murphy@arm.com, cohuck@redhat.com, eric.auger@redhat.com, nicolinc@nvidia.com, kvm@vger.kernel.org, mjrosato@linux.ibm.com, chao.p.peng@linux.intel.com, yi.y.sun@linux.intel.com, peterx@redhat.com, jasowang@redhat.com, shameerali.kolothum.thodi@huawei.com, lulu@redhat.com, suravee.suthikulpanit@amd.com, intel-gvt-dev@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-s390@vger.kernel.org, xudong.hao@intel.com, yan.y.zhao@intel.com, terrence.xu@intel.com, yanting.jiang@intel.com, zhenzhong.duan@intel.com, clegoate@redhat.com Subject: Re: [PATCH v12 07/24] vfio: Block device access via device fd until device is opened Message-ID: <20230612155210.5fd3579f.alex.williamson@redhat.com> In-Reply-To: <20230602121653.80017-8-yi.l.liu@intel.com> References: <20230602121653.80017-1-yi.l.liu@intel.com> <20230602121653.80017-8-yi.l.liu@intel.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.35; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On Fri, 2 Jun 2023 05:16:36 -0700 Yi Liu wrote: > Allow the vfio_device file to be in a state where the device FD is > opened but the device cannot be used by userspace (i.e. its .open_device() > hasn't been called). This inbetween state is not used when the device > FD is spawned from the group FD, however when we create the device FD > directly by opening a cdev it will be opened in the blocked state. > > The reason for the inbetween state is that userspace only gets a FD but > doesn't gain access permission until binding the FD to an iommufd. So in > the blocked state, only the bind operation is allowed. Completing bind > will allow user to further access the device. > > This is implemented by adding a flag in struct vfio_device_file to mark > the blocked state and using a simple smp_load_acquire() to obtain the > flag value and serialize all the device setup with the thread accessing > this device. > > Following this lockless scheme, it can safely handle the device FD > unbound->bound but it cannot handle bound->unbound. To allow this we'd > need to add a lock on all the vfio ioctls which seems costly. So once > device FD is bound, it remains bound until the FD is closed. > > Suggested-by: Jason Gunthorpe > Reviewed-by: Kevin Tian > Reviewed-by: Jason Gunthorpe > Reviewed-by: Eric Auger > Tested-by: Terrence Xu > Tested-by: Nicolin Chen > Tested-by: Matthew Rosato > Tested-by: Yanting Jiang > Tested-by: Shameer Kolothum > Signed-off-by: Yi Liu > --- > drivers/vfio/group.c | 11 ++++++++++- > drivers/vfio/vfio.h | 1 + > drivers/vfio/vfio_main.c | 16 ++++++++++++++++ > 3 files changed, 27 insertions(+), 1 deletion(-) > > diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c > index caf53716ddb2..088dd34c8931 100644 > --- a/drivers/vfio/group.c > +++ b/drivers/vfio/group.c > @@ -194,9 +194,18 @@ static int vfio_df_group_open(struct vfio_device_file *df) > df->iommufd = device->group->iommufd; > > ret = vfio_df_open(df); > - if (ret) > + if (ret) { > df->iommufd = NULL; > + goto out_put_kvm; > + } > + > + /* > + * Paired with smp_load_acquire() in vfio_device_fops::ioctl/ > + * read/write/mmap and vfio_file_has_device_access() > + */ > + smp_store_release(&df->access_granted, true); > > +out_put_kvm: > if (device->open_count == 0) > vfio_device_put_kvm(device); > > diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h > index f9eb52eb9ed7..fdf2fc73f880 100644 > --- a/drivers/vfio/vfio.h > +++ b/drivers/vfio/vfio.h > @@ -18,6 +18,7 @@ struct vfio_container; > > struct vfio_device_file { > struct vfio_device *device; > + bool access_granted; Should we make this a more strongly defined data type and later move devid (u32) here to partially fill the hole created? I think this is being placed towards the front of the data structure for cache line locality given this is a hot path for file operations. But bool types have an implementation dependent size, making them difficult to pack. Also there will be a tendency to want to make this a bit field, which is probably not compatible with the smp lockless operations being used here. We might get in front of these issues if we just define it as a u8 now. Thanks, Alex > spinlock_t kvm_ref_lock; /* protect kvm field */ > struct kvm *kvm; > struct iommufd_ctx *iommufd; /* protected by struct vfio_device_set::lock */ > diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c > index a3c5817fc545..4c8b7713dc3d 100644 > --- a/drivers/vfio/vfio_main.c > +++ b/drivers/vfio/vfio_main.c > @@ -1129,6 +1129,10 @@ static long vfio_device_fops_unl_ioctl(struct file *filep, > struct vfio_device *device = df->device; > int ret; > > + /* Paired with smp_store_release() following vfio_df_open() */ > + if (!smp_load_acquire(&df->access_granted)) > + return -EINVAL; > + > ret = vfio_device_pm_runtime_get(device); > if (ret) > return ret; > @@ -1156,6 +1160,10 @@ static ssize_t vfio_device_fops_read(struct file *filep, char __user *buf, > struct vfio_device_file *df = filep->private_data; > struct vfio_device *device = df->device; > > + /* Paired with smp_store_release() following vfio_df_open() */ > + if (!smp_load_acquire(&df->access_granted)) > + return -EINVAL; > + > if (unlikely(!device->ops->read)) > return -EINVAL; > > @@ -1169,6 +1177,10 @@ static ssize_t vfio_device_fops_write(struct file *filep, > struct vfio_device_file *df = filep->private_data; > struct vfio_device *device = df->device; > > + /* Paired with smp_store_release() following vfio_df_open() */ > + if (!smp_load_acquire(&df->access_granted)) > + return -EINVAL; > + > if (unlikely(!device->ops->write)) > return -EINVAL; > > @@ -1180,6 +1192,10 @@ static int vfio_device_fops_mmap(struct file *filep, struct vm_area_struct *vma) > struct vfio_device_file *df = filep->private_data; > struct vfio_device *device = df->device; > > + /* Paired with smp_store_release() following vfio_df_open() */ > + if (!smp_load_acquire(&df->access_granted)) > + return -EINVAL; > + > if (unlikely(!device->ops->mmap)) > return -EINVAL; >