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

Cornelia Huck
2019-05-27T10:38:02Z

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)