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Message-ID: <ZoKTBU2VaW0IazUi@yzhao56-desk.sh.intel.com>
Date: Mon, 1 Jul 2024 19:29:09 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Yi Liu <yi.l.liu@...el.com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<alex.williamson@...hat.com>, <kevin.tian@...el.com>, <jgg@...dia.com>,
<peterx@...hat.com>, <ajones@...tanamicro.com>
Subject: Re: [PATCH] vfio: Reuse file f_inode as vfio device inode
On Mon, Jul 01, 2024 at 03:54:19PM +0800, Yi Liu wrote:
> On 2024/6/17 17:53, Yan Zhao wrote:
> > Reuse file f_inode as vfio device inode and associate pseudo path file
> > directly to inode allocated in vfio fs.
> >
> > Currently, vfio device is opened via 2 ways:
> > 1) via cdev open
> > vfio device is opened with a cdev device with file f_inode and address
> > space associated with a cdev inode;
> > 2) via VFIO_GROUP_GET_DEVICE_FD ioctl
> > vfio device is opened via a pseudo path file with file f_inode and
> > address space associated with an inode in anon_inode_fs.
> >
>
> You can simply say the cdev path and group path. :)
Ok, if they are well-known terms.
>
> > In commit b7c5e64fecfa ("vfio: Create vfio_fs_type with inode per device"),
> > an inode in vfio fs is allocated for each vfio device. However, this inode
> > in vfio fs is only used to assign its address space to that of a file
> > associated with another cdev inode or an inode in anon_inode_fs.
> >
> > This patch
> > - reuses cdev device inode as the vfio device inode when it's opened via
> > cdev way;
> > - allocates an inode in vfio fs, associate it to the pseudo path file,
> > and save it as the vfio device inode when the vfio device is opened via
> > VFIO_GROUP_GET_DEVICE_FD ioctl.
>
> So Alex's prior series only makes use of the i_mapping of the inode instead
> of associating the inode with the pseudo path file?
Right.
> > File address space will then point automatically to the address space of
> > the vfio device inode. Tools like unmap_mapping_range() can then zap all
> > vmas associated with the vfio device.
> >
> > Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
> > ---
> > drivers/vfio/device_cdev.c | 9 ++++---
> > drivers/vfio/group.c | 21 ++--------------
> > drivers/vfio/vfio.h | 2 ++
> > drivers/vfio/vfio_main.c | 49 +++++++++++++++++++++++++++-----------
> > 4 files changed, 43 insertions(+), 38 deletions(-)
> >
> > diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
> > index bb1817bd4ff3..a4eec8e88f5c 100644
> > --- a/drivers/vfio/device_cdev.c
> > +++ b/drivers/vfio/device_cdev.c
> > @@ -40,12 +40,11 @@ int vfio_device_fops_cdev_open(struct inode *inode, struct file *filep)
> > filep->private_data = df;
> > /*
> > - * Use the pseudo fs inode on the device to link all mmaps
> > - * to the same address space, allowing us to unmap all vmas
> > - * associated to this device using unmap_mapping_range().
> > + * mmaps are linked to the address space of the inode of device cdev.
> > + * Save the inode of device cdev in device->inode to allow
> > + * unmap_mapping_range() to unmap all vmas.
> > */
> > - filep->f_mapping = device->inode->i_mapping;
> > -
> > + device->inode = inode;
> > return 0;
> > err_put_registration:
> > diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
> > index ded364588d29..aaef188003b6 100644
> > --- a/drivers/vfio/group.c
> > +++ b/drivers/vfio/group.c
> > @@ -268,31 +268,14 @@ static struct file *vfio_device_open_file(struct vfio_device *device)
> > if (ret)
> > goto err_free;
> > - /*
> > - * We can't use anon_inode_getfd() because we need to modify
> > - * the f_mode flags directly to allow more than just ioctls
> > - */
> > - filep = anon_inode_getfile("[vfio-device]", &vfio_device_fops,
> > - df, O_RDWR);
> > + filep = vfio_device_get_pseudo_file(device);
> > if (IS_ERR(filep)) {
> > ret = PTR_ERR(filep);
> > goto err_close_device;
> > }
> > -
> > - /*
> > - * TODO: add an anon_inode interface to do this.
> > - * Appears to be missing by lack of need rather than
> > - * explicitly prevented. Now there's need.
> > - */
> > + filep->private_data = df;
> > filep->f_mode |= (FMODE_PREAD | FMODE_PWRITE);
> > - /*
> > - * Use the pseudo fs inode on the device to link all mmaps
> > - * to the same address space, allowing us to unmap all vmas
> > - * associated to this device using unmap_mapping_range().
> > - */
> > - filep->f_mapping = device->inode->i_mapping;
> > -
> > if (device->group->type == VFIO_NO_IOMMU)
> > dev_warn(device->dev, "vfio-noiommu device opened by user "
> > "(%s:%d)\n", current->comm, task_pid_nr(current));
> > diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> > index 50128da18bca..1f8915f79fbb 100644
> > --- a/drivers/vfio/vfio.h
> > +++ b/drivers/vfio/vfio.h
> > @@ -35,6 +35,7 @@ struct vfio_device_file *
> > vfio_allocate_device_file(struct vfio_device *device);
> > extern const struct file_operations vfio_device_fops;
> > +struct file *vfio_device_get_pseudo_file(struct vfio_device *device);
> > #ifdef CONFIG_VFIO_NOIOMMU
> > extern bool vfio_noiommu __read_mostly;
> > @@ -420,6 +421,7 @@ static inline void vfio_cdev_cleanup(void)
> > {
> > }
> > #endif /* CONFIG_VFIO_DEVICE_CDEV */
> > +struct file *vfio_device_get_pseduo_file(struct vfio_device *device);
> > #if IS_ENABLED(CONFIG_VFIO_VIRQFD)
> > int __init vfio_virqfd_init(void);
> > diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> > index a5a62d9d963f..e81d0f910c70 100644
> > --- a/drivers/vfio/vfio_main.c
> > +++ b/drivers/vfio/vfio_main.c
> > @@ -192,7 +192,6 @@ static void vfio_device_release(struct device *dev)
> > if (device->ops->release)
> > device->ops->release(device);
> > - iput(device->inode);
> > simple_release_fs(&vfio.vfs_mount, &vfio.fs_count);
> > kvfree(device);
> > }
> > @@ -248,20 +247,50 @@ static struct file_system_type vfio_fs_type = {
> > .kill_sb = kill_anon_super,
> > };
> > -static struct inode *vfio_fs_inode_new(void)
> > +/*
> > + * Alloc pseudo file from inode associated of vfio.vfs_mount.
>
> nit: s/Alloc/Allocate/ and s/of/with/
>
> > + * This is called when vfio device is opened via pseudo file.
>
> group path might be better. Is this pseudo file only needed for the device
> files opened in the group path? If so, might be helpful to move the related
> codes into group.c.
Yes. I also planed to move the this to group.c in v2 :)
>
> > + * mmaps are linked to the address space of the inode of the pseudo file.
> > + * Save the inode in device->inode for unmap_mapping_range() to unmap all vmas.
> > + */
> > +struct file *vfio_device_get_pseudo_file(struct vfio_device *device)
> > {
> > + const struct file_operations *fops = &vfio_device_fops;
> > struct inode *inode;
> > + struct file *filep;
> > int ret;
> > + if (!fops_get(fops))
> > + return ERR_PTR(-ENODEV);
> > +
> > ret = simple_pin_fs(&vfio_fs_type, &vfio.vfs_mount, &vfio.fs_count);
> > if (ret)
> > - return ERR_PTR(ret);
> > + goto err_pin_fs;
> > inode = alloc_anon_inode(vfio.vfs_mount->mnt_sb);
> > - if (IS_ERR(inode))
> > - simple_release_fs(&vfio.vfs_mount, &vfio.fs_count);
> > + if (IS_ERR(inode)) {
> > + ret = PTR_ERR(inode);
> > + goto err_inode;
> > + }
> > +
> > + filep = alloc_file_pseudo(inode, vfio.vfs_mount, "[vfio-device]",
> > + O_RDWR, fops);
> > +
> > + if (IS_ERR(filep)) {
> > + ret = PTR_ERR(filep);
> > + goto err_file;
> > + }
> > + device->inode = inode;
>
> The group path allows multiple device fd get, hence this will set the
> device->inode multiple times. It does not look good. Setting it once
> should be enough?
Will make the multipl opens to use the same vfio inode, as in [1].
[1] https://lore.kernel.org/all/Zn02BUdJ7kvOg6Vw@yzhao56-desk.sh.intel.com/
>
> > + return filep;
> > +
> > +err_file:
> > + iput(inode);
>
> If the vfio_device_get_pseudo_file() succeeds, who will put inode? I
> noticed all the other iput() of this file are removed.
On success, the inode ref count is moved to the file and put in
vfio_device_fops_release().
The prevous iput() is only required because that inode is not associated
with any file.
> > +err_inode:
> > + simple_release_fs(&vfio.vfs_mount, &vfio.fs_count);
> > +err_pin_fs:
> > + fops_put(fops);
> > - return inode;
> > + return ERR_PTR(ret);
> > }
> > /*
> > @@ -282,11 +311,6 @@ static int vfio_init_device(struct vfio_device *device, struct device *dev,
> > init_completion(&device->comp);
> > device->dev = dev;
> > device->ops = ops;
> > - device->inode = vfio_fs_inode_new();
> > - if (IS_ERR(device->inode)) {
> > - ret = PTR_ERR(device->inode);
> > - goto out_inode;
> > - }
> > if (ops->init) {
> > ret = ops->init(device);
> > @@ -301,9 +325,6 @@ static int vfio_init_device(struct vfio_device *device, struct device *dev,
> > return 0;
> > out_uninit:
> > - iput(device->inode);
> > - simple_release_fs(&vfio.vfs_mount, &vfio.fs_count);
> > -out_inode:
> > vfio_release_device_set(device);
> > ida_free(&vfio.device_ida, device->index);
> > return ret;
> >
> > base-commit: 6ba59ff4227927d3a8530fc2973b80e94b54d58f
>
> --
> Regards,
> Yi Liu
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