linux-kernel - Re: [PATCH v8 4/4] vfio: Support IO page table replacement

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Message-ID: <20230726113424.0e016e07.alex.williamson@redhat.com>
Date:   Wed, 26 Jul 2023 11:34:24 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     <jgg@...dia.com>, <kevin.tian@...el.com>, <yi.l.liu@...el.com>,
        <joro@...tes.org>, <will@...nel.org>, <robin.murphy@....com>,
        <shuah@...nel.org>, <linux-kernel@...r.kernel.org>,
        <iommu@...ts.linux.dev>, <kvm@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <mjrosato@...ux.ibm.com>,
        <farman@...ux.ibm.com>
Subject: Re: [PATCH v8 4/4] vfio: Support IO page table replacement

On Mon, 24 Jul 2023 12:47:07 -0700
Nicolin Chen <nicolinc@...dia.com> wrote:

> Now both the physical path and the emulated path should support an IO page
> table replacement. Call iommufd_device_replace/iommufd_access_replace(),
> when vdev->iommufd_attached is true.
> 
> Also update the VFIO_DEVICE_ATTACH_IOMMUFD_PT kdoc in the uAPI header.
> 
> Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> ---
>  drivers/vfio/iommufd.c    | 11 ++++++-----
>  include/uapi/linux/vfio.h |  6 ++++++
>  2 files changed, 12 insertions(+), 5 deletions(-)

Reviewed-by: Alex Williamson <alex.williamson@...hat.com>

> 
> diff --git a/drivers/vfio/iommufd.c b/drivers/vfio/iommufd.c
> index 4d84904fd927..82eba6966fa5 100644
> --- a/drivers/vfio/iommufd.c
> +++ b/drivers/vfio/iommufd.c
> @@ -146,9 +146,9 @@ int vfio_iommufd_physical_attach_ioas(struct vfio_device *vdev, u32 *pt_id)
>  		return -EINVAL;
>  
>  	if (vdev->iommufd_attached)
> -		return -EBUSY;
> -
> -	rc = iommufd_device_attach(vdev->iommufd_device, pt_id);
> +		rc = iommufd_device_replace(vdev->iommufd_device, pt_id);
> +	else
> +		rc = iommufd_device_attach(vdev->iommufd_device, pt_id);
>  	if (rc)
>  		return rc;
>  	vdev->iommufd_attached = true;
> @@ -223,8 +223,9 @@ int vfio_iommufd_emulated_attach_ioas(struct vfio_device *vdev, u32 *pt_id)
>  	lockdep_assert_held(&vdev->dev_set->lock);
>  
>  	if (vdev->iommufd_attached)
> -		return -EBUSY;
> -	rc = iommufd_access_attach(vdev->iommufd_access, *pt_id);
> +		rc = iommufd_access_replace(vdev->iommufd_access, *pt_id);
> +	else
> +		rc = iommufd_access_attach(vdev->iommufd_access, *pt_id);
>  	if (rc)
>  		return rc;
>  	vdev->iommufd_attached = true;
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index fa06e3eb4955..537157ff8670 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -939,6 +939,12 @@ struct vfio_device_bind_iommufd {
>   * Undo by VFIO_DEVICE_DETACH_IOMMUFD_PT or device fd close.  This is only
>   * allowed on cdev fds.
>   *
> + * If a vfio device is currently attached to a valid hw_pagetable, without doing
> + * a VFIO_DEVICE_DETACH_IOMMUFD_PT, a second VFIO_DEVICE_ATTACH_IOMMUFD_PT ioctl
> + * passing in another hw_pagetable (hwpt) id is allowed. This action, also known
> + * as a hw_pagetable replacement, will replace the device's currently attached
> + * hw_pagetable with a new hw_pagetable corresponding to the given pt_id.
> + *
>   * Return: 0 on success, -errno on failure.
>   */
>  struct vfio_device_attach_iommufd_pt {