KVM Archive on lore.kernel.org
 help / color / Atom feed
From: Jason Wang <jasowang@redhat.com>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: "mst@redhat.com" <mst@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"virtualization@lists.linux-foundation.org" 
	<virtualization@lists.linux-foundation.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"tiwei.bie@intel.com" <tiwei.bie@intel.com>,
	"maxime.coquelin@redhat.com" <maxime.coquelin@redhat.com>,
	"cunming.liang@intel.com" <cunming.liang@intel.com>,
	"zhihong.wang@intel.com" <zhihong.wang@intel.com>,
	"rob.miller@broadcom.com" <rob.miller@broadcom.com>,
	"xiao.w.wang@intel.com" <xiao.w.wang@intel.com>,
	"haotian.wang@sifive.com" <haotian.wang@sifive.com>,
	"lingshan.zhu@intel.com" <lingshan.zhu@intel.com>,
	"eperezma@redhat.com" <eperezma@redhat.com>,
	"lulu@redhat.com" <lulu@redhat.com>,
	Parav Pandit <parav@mellanox.com>,
	"kevin.tian@intel.com" <kevin.tian@intel.com>,
	"stefanha@redhat.com" <stefanha@redhat.com>,
	"rdunlap@infradead.org" <rdunlap@infradead.org>,
	"hch@infradead.org" <hch@infradead.org>,
	"aadam@redhat.com" <aadam@redhat.com>,
	"jakub.kicinski@netronome.com" <jakub.kicinski@netronome.com>,
	Jiri Pirko <jiri@mellanox.com>,
	Shahaf Shuler <shahafs@mellanox.com>,
	"hanand@xilinx.com" <hanand@xilinx.com>,
	"mhabets@solarflare.com" <mhabets@solarflare.com>
Subject: Re: [PATCH 4/5] virtio: introduce a vDPA based transport
Date: Fri, 17 Jan 2020 17:32:35 +0800
Message-ID: <8e8aa4b7-4948-5719-9618-e28daffba1a5@redhat.com> (raw)
In-Reply-To: <20200116153807.GI20978@mellanox.com>


On 2020/1/16 下午11:38, Jason Gunthorpe wrote:
> On Thu, Jan 16, 2020 at 08:42:30PM +0800, Jason Wang wrote:
>> diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
>> new file mode 100644
>> index 000000000000..86936e5e7ec3
>> +++ b/drivers/virtio/virtio_vdpa.c
>> @@ -0,0 +1,400 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * VIRTIO based driver for vDPA device
>> + *
>> + * Copyright (c) 2020, Red Hat. All rights reserved.
>> + *     Author: Jason Wang <jasowang@redhat.com>
>> + *
>> + */
>> +
>> +#include <linux/init.h>
>> +#include <linux/module.h>
>> +#include <linux/device.h>
>> +#include <linux/kernel.h>
>> +#include <linux/slab.h>
>> +#include <linux/uuid.h>
>> +#include <linux/virtio.h>
>> +#include <linux/vdpa.h>
>> +#include <linux/virtio_config.h>
>> +#include <linux/virtio_ring.h>
>> +
>> +#define MOD_VERSION  "0.1"
>> +#define MOD_AUTHOR   "Jason Wang <jasowang@redhat.com>"
>> +#define MOD_DESC     "vDPA bus driver for virtio devices"
>> +#define MOD_LICENSE  "GPL v2"
>> +
>> +#define to_virtio_vdpa_device(dev) \
>> +	container_of(dev, struct virtio_vdpa_device, vdev)
> Should be a static function


Ok.


>
>> +struct virtio_vdpa_device {
>> +	struct virtio_device vdev;
>> +	struct vdpa_device *vdpa;
>> +	u64 features;
>> +
>> +	/* The lock to protect virtqueue list */
>> +	spinlock_t lock;
>> +	/* List of virtio_vdpa_vq_info */
>> +	struct list_head virtqueues;
>> +};
>> +
>> +struct virtio_vdpa_vq_info {
>> +	/* the actual virtqueue */
>> +	struct virtqueue *vq;
>> +
>> +	/* the list node for the virtqueues list */
>> +	struct list_head node;
>> +};
>> +
>> +static struct vdpa_device *vd_get_vdpa(struct virtio_device *vdev)
>> +{
>> +	struct virtio_vdpa_device *vd_dev = to_virtio_vdpa_device(vdev);
>> +	struct vdpa_device *vdpa = vd_dev->vdpa;
>> +
>> +	return vdpa;
> Bit of a long way to say
>
>    return to_virtio_vdpa_device(vdev)->vdpa
>
> ?


Right.


>
>> +err_vq:
>> +	vring_del_virtqueue(vq);
>> +error_new_virtqueue:
>> +	ops->set_vq_ready(vdpa, index, 0);
>> +	WARN_ON(ops->get_vq_ready(vdpa, index));
> A warn_on during error unwind? Sketchy, deserves a comment I think


Yes, it's a hint of bug in the vDPA driver. Will add a comment.


>
>> +static void virtio_vdpa_release_dev(struct device *_d)
>> +{
>> +	struct virtio_device *vdev =
>> +	       container_of(_d, struct virtio_device, dev);
>> +	struct virtio_vdpa_device *vd_dev =
>> +	       container_of(vdev, struct virtio_vdpa_device, vdev);
>> +	struct vdpa_device *vdpa = vd_dev->vdpa;
>> +
>> +	devm_kfree(&vdpa->dev, vd_dev);
>> +}
> It is unusual for the release function to not be owned by the
> subsystem, through the class.


This is how virtio_pci and virtio_mmio work now. Virtio devices may have 
different transports which require different release functions. I think 
this is the reason why virtio


> I'm not sure there are enough module ref
> counts to ensure that this function is not unloaded?


Let me double check this.


>
> Usually to make this all work sanely the subsytem provides some
> allocation function
>
>   vdpa_dev = vdpa_alloc_dev(parent, ops, sizeof(struct virtio_vdpa_device))
>   struct virtio_vdpa_device *priv = vdpa_priv(vdpa_dev)
>
> Then the subsystem naturally owns all the memory.
>
> Otherwise it gets tricky to ensure that the module doesn't unload
> before all the krefs are put.


I see.


>
>> +
>> +static int virtio_vdpa_probe(struct device *dev)
>> +{
>> +	struct vdpa_device *vdpa = dev_to_vdpa(dev);
> The probe function for a class should accept the classes type already,
> no casting.


Right.


>
>> +	const struct vdpa_config_ops *ops = vdpa->config;
>> +	struct virtio_vdpa_device *vd_dev;
>> +	int rc;
>> +
>> +	vd_dev = devm_kzalloc(dev, sizeof(*vd_dev), GFP_KERNEL);
>> +	if (!vd_dev)
>> +		return -ENOMEM;
> This is not right, the struct device lifetime is controled by a kref,
> not via devm. If you want to use a devm unwind then the unwind is
> put_device, not devm_kfree.


I'm not sure I get the point here. The lifetime is bound to underlying 
vDPA device and devres allow to be freed before the vpda device is 
released. But I agree using devres of underlying vdpa device looks wired.


>
> In this simple situation I don't see a reason to use devm.
>
>> +	vd_dev->vdev.dev.parent = &vdpa->dev;
>> +	vd_dev->vdev.dev.release = virtio_vdpa_release_dev;
>> +	vd_dev->vdev.config = &virtio_vdpa_config_ops;
>> +	vd_dev->vdpa = vdpa;
>> +	INIT_LIST_HEAD(&vd_dev->virtqueues);
>> +	spin_lock_init(&vd_dev->lock);
>> +
>> +	vd_dev->vdev.id.device = ops->get_device_id(vdpa);
>> +	if (vd_dev->vdev.id.device == 0)
>> +		return -ENODEV;
>> +
>> +	vd_dev->vdev.id.vendor = ops->get_vendor_id(vdpa);
>> +	rc = register_virtio_device(&vd_dev->vdev);
>> +	if (rc)
>> +		put_device(dev);
> And a ugly unwind like this is why you want to have device_initialize()
> exposed to the driver,


In this context, which "driver" did you mean here? (Note, virtio-vdpa is 
the driver for vDPA bus here).


>   so there is a clear pairing that calling
> device_initialize() must be followed by put_device. This should also
> use the goto unwind style
>
>> +	else
>> +		dev_set_drvdata(dev, vd_dev);
>> +
>> +	return rc;
>> +}
>> +
>> +static void virtio_vdpa_remove(struct device *dev)
>> +{
> Remove should also already accept the right type


Yes.


>
>> +	struct virtio_vdpa_device *vd_dev = dev_get_drvdata(dev);
>> +
>> +	unregister_virtio_device(&vd_dev->vdev);
>> +}
>> +
>> +static struct vdpa_driver virtio_vdpa_driver = {
>> +	.drv = {
>> +		.name	= "virtio_vdpa",
>> +	},
>> +	.probe	= virtio_vdpa_probe,
>> +	.remove = virtio_vdpa_remove,
>> +};
> Still a little unclear on binding, is this supposed to bind to all
> vdpa devices?


Yes, it expected to drive all vDPA devices.


>
> Where is the various THIS_MODULE's I expect to see in a scheme like
> this?
>
> All function pointers must be protected by a held module reference
> count, ie the above probe/remove and all the pointers in ops.


Will double check, since I don't see this in other virtio transport 
drivers (PCI or MMIO).


>
>> +static int __init virtio_vdpa_init(void)
>> +{
>> +	return register_vdpa_driver(&virtio_vdpa_driver);
>> +}
>> +
>> +static void __exit virtio_vdpa_exit(void)
>> +{
>> +	unregister_vdpa_driver(&virtio_vdpa_driver);
>> +}
>> +
>> +module_init(virtio_vdpa_init)
>> +module_exit(virtio_vdpa_exit)
> Best to provide the usual 'module_pci_driver' like scheme for this
> boiler plate.


Ok.


>
>> +MODULE_VERSION(MOD_VERSION);
>> +MODULE_LICENSE(MOD_LICENSE);
>> +MODULE_AUTHOR(MOD_AUTHOR);
>> +MODULE_DESCRIPTION(MOD_DESC);
> Why the indirection with 2nd defines?


Will fix.

Thanks


>
> Jason
>


  reply index

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16 12:42 [PATCH 0/5] vDPA support Jason Wang
2020-01-16 12:42 ` [PATCH 1/5] vhost: factor out IOTLB Jason Wang
2020-01-17  4:14   ` Randy Dunlap
2020-01-17  9:34     ` Jason Wang
2020-01-18  0:01   ` kbuild test robot
2020-01-18  0:40   ` kbuild test robot
2020-01-16 12:42 ` [PATCH 2/5] vringh: IOTLB support Jason Wang
2020-01-17 21:54   ` kbuild test robot
2020-01-17 22:33   ` kbuild test robot
2020-01-16 12:42 ` [PATCH 3/5] vDPA: introduce vDPA bus Jason Wang
2020-01-16 15:22   ` Jason Gunthorpe
2020-01-17  3:03     ` Jason Wang
2020-01-17 13:54       ` Jason Gunthorpe
2020-01-20  7:50         ` Jason Wang
2020-01-20 12:17         ` Michael S. Tsirkin
2020-01-20 17:50           ` Jason Gunthorpe
2020-01-20 21:56             ` Michael S. Tsirkin
2020-01-21 14:12               ` Jason Gunthorpe
2020-01-21 14:15                 ` Michael S. Tsirkin
2020-01-21 14:16                   ` Jason Gunthorpe
2020-01-21  8:40       ` Tian, Kevin
2020-01-21  9:41         ` Jason Wang
2020-01-17  4:16   ` Randy Dunlap
2020-01-17  9:34     ` Jason Wang
2020-01-17 12:13   ` Michael S. Tsirkin
2020-01-17 13:52     ` Jason Wang
     [not found]       ` <CAJPjb1+fG9L3=iKbV4Vn13VwaeDZZdcfBPvarogF_Nzhk+FnKg@mail.gmail.com>
2020-01-19  9:07         ` Shahaf Shuler
2020-01-19  9:59           ` Michael S. Tsirkin
2020-01-20  8:44             ` Jason Wang
2020-01-20 12:09               ` Michael S. Tsirkin
2020-01-21  3:32                 ` Jason Wang
2020-01-20  8:43           ` Jason Wang
2020-01-20 17:49             ` Jason Gunthorpe
2020-01-20 20:51               ` Shahaf Shuler
2020-01-20 21:25                 ` Michael S. Tsirkin
2020-01-20 21:47                   ` Shahaf Shuler
2020-01-20 21:59                     ` Michael S. Tsirkin
2020-01-21  6:01                       ` Shahaf Shuler
2020-01-21  7:57                         ` Jason Wang
2020-01-21 14:07                   ` Jason Gunthorpe
2020-01-21 14:16                     ` Michael S. Tsirkin
2020-01-20 21:48               ` Michael S. Tsirkin
2020-01-21  4:00               ` Jason Wang
2020-01-21  5:47                 ` Michael S. Tsirkin
2020-01-21  8:00                   ` Jason Wang
2020-01-21  8:15                     ` Michael S. Tsirkin
2020-01-21  8:35                       ` Jason Wang
2020-01-21 11:09                         ` Shahaf Shuler
2020-01-22  6:36                           ` Jason Wang
2020-01-21 14:05                       ` Jason Gunthorpe
2020-01-21 14:17                         ` Michael S. Tsirkin
2020-01-22  6:18                           ` Jason Wang
2020-01-20  8:19         ` Jason Wang
2020-01-16 12:42 ` [PATCH 4/5] virtio: introduce a vDPA based transport Jason Wang
2020-01-16 15:38   ` Jason Gunthorpe
2020-01-17  9:32     ` Jason Wang [this message]
2020-01-17 14:00       ` Jason Gunthorpe
2020-01-20  7:52         ` Jason Wang
2020-01-17  4:10   ` Randy Dunlap
2020-01-16 12:42 ` [PATCH 5/5] vdpasim: vDPA device simulator Jason Wang
2020-01-16 15:47   ` Jason Gunthorpe
2020-01-17  9:32     ` Jason Wang
2020-01-17 14:10       ` Jason Gunthorpe
2020-01-20  8:01         ` Jason Wang
2020-02-04  4:19         ` Jason Wang
2020-01-17  4:12   ` Randy Dunlap
2020-01-17  9:35     ` Jason Wang
2020-01-18 18:18   ` kbuild test robot
2020-01-28  3:32   ` Dan Carpenter
2020-02-04  4:07     ` Jason Wang
2020-02-04  8:21   ` Zhu Lingshan
2020-02-04  8:28     ` Jason Wang
2020-02-04 12:52       ` Jason Gunthorpe
2020-02-05  3:14         ` Jason Wang
2020-01-21  8:44 ` [PATCH 0/5] vDPA support Tian, Kevin
2020-01-21  9:39   ` Jason Wang

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=8e8aa4b7-4948-5719-9618-e28daffba1a5@redhat.com \
    --to=jasowang@redhat.com \
    --cc=aadam@redhat.com \
    --cc=cunming.liang@intel.com \
    --cc=eperezma@redhat.com \
    --cc=hanand@xilinx.com \
    --cc=haotian.wang@sifive.com \
    --cc=hch@infradead.org \
    --cc=jakub.kicinski@netronome.com \
    --cc=jgg@mellanox.com \
    --cc=jiri@mellanox.com \
    --cc=kevin.tian@intel.com \
    --cc=kvm@vger.kernel.org \
    --cc=lingshan.zhu@intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=lulu@redhat.com \
    --cc=maxime.coquelin@redhat.com \
    --cc=mhabets@solarflare.com \
    --cc=mst@redhat.com \
    --cc=netdev@vger.kernel.org \
    --cc=parav@mellanox.com \
    --cc=rdunlap@infradead.org \
    --cc=rob.miller@broadcom.com \
    --cc=shahafs@mellanox.com \
    --cc=stefanha@redhat.com \
    --cc=tiwei.bie@intel.com \
    --cc=virtualization@lists.linux-foundation.org \
    --cc=xiao.w.wang@intel.com \
    --cc=zhihong.wang@intel.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

KVM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvm/0 kvm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvm kvm/ https://lore.kernel.org/kvm \
		kvm@vger.kernel.org
	public-inbox-index kvm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.kvm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git