Re: [PATCH v2 3/8] s390/cio: add basic protected virtualization support

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 23 May 2019 18:22:04 +0200
Michael Mueller <mimu@linux.ibm.com> wrote:

> From: Halil Pasic <pasic@linux.ibm.com>
> 
> As virtio-ccw devices are channel devices, we need to use the dma area
> for any communication with the hypervisor.
> 
> It handles neither QDIO in the common code, nor any device type specific
> stuff (like channel programs constructed by the DASD driver).
> 
> An interesting side effect is that virtio structures are now going to
> get allocated in 31 bit addressable storage.
> 
> Signed-off-by: Halil Pasic <pasic@linux.ibm.com>

[Side note: you really should add your s-o-b if you send someone else's
patches... if Halil ends up committing them, it's fine, though.]

> ---
>  arch/s390/include/asm/ccwdev.h   |  4 +++
>  drivers/s390/cio/ccwreq.c        |  9 +++---
>  drivers/s390/cio/device.c        | 64 +++++++++++++++++++++++++++++++++-------
>  drivers/s390/cio/device_fsm.c    | 53 ++++++++++++++++++++-------------
>  drivers/s390/cio/device_id.c     | 20 +++++++------
>  drivers/s390/cio/device_ops.c    | 21 +++++++++++--
>  drivers/s390/cio/device_pgid.c   | 22 +++++++-------
>  drivers/s390/cio/device_status.c | 24 +++++++--------
>  drivers/s390/cio/io_sch.h        | 20 +++++++++----
>  drivers/s390/virtio/virtio_ccw.c | 10 -------
>  10 files changed, 164 insertions(+), 83 deletions(-)
> 

(...)

> @@ -1593,20 +1622,31 @@ struct ccw_device * __init ccw_device_create_console(struct ccw_driver *drv)
>  		return ERR_CAST(sch);
>  
>  	io_priv = kzalloc(sizeof(*io_priv), GFP_KERNEL | GFP_DMA);
> -	if (!io_priv) {
> -		put_device(&sch->dev);
> -		return ERR_PTR(-ENOMEM);
> -	}
> +	if (!io_priv)
> +		goto err_priv;
> +	io_priv->dma_area = dma_alloc_coherent(&sch->dev,
> +				sizeof(*io_priv->dma_area),
> +				&io_priv->dma_area_dma, GFP_KERNEL);

Even though we'll only end up here for 3215 or 3270 consoles, this sent
me looking.

This code is invoked via console_init(). A few lines down in
start_kernel(), we have

        /*                                                                       
         * This needs to be called before any devices perform DMA                
         * operations that might use the SWIOTLB bounce buffers. It will         
         * mark the bounce buffers as decrypted so that their usage will         
         * not cause "plain-text" data to be decrypted when accessed.            
         */
        mem_encrypt_init();

So, I'm wondering if creating the console device interacts in any way
with the memory encryption interface?

[Does basic recognition work if you start a protected virt guest with a
3270 console? I realize that the console is unlikely to work, but that
should at least exercise this code path.]

> +	if (!io_priv->dma_area)
> +		goto err_dma_area;
>  	set_io_private(sch, io_priv);
>  	cdev = io_subchannel_create_ccwdev(sch);
>  	if (IS_ERR(cdev)) {
>  		put_device(&sch->dev);
> +		dma_free_coherent(&sch->dev, sizeof(*io_priv->dma_area),
> +				  io_priv->dma_area, io_priv->dma_area_dma);
>  		kfree(io_priv);
>  		return cdev;
>  	}
>  	cdev->drv = drv;
>  	ccw_device_set_int_class(cdev);
>  	return cdev;
> +
> +err_dma_area:
> +		kfree(io_priv);
> +err_priv:
> +	put_device(&sch->dev);
> +	return ERR_PTR(-ENOMEM);
>  }
>  
>  void __init ccw_device_destroy_console(struct ccw_device *cdev)