Re: [PATCH 06/10] s390/cio: add basic protected virtualization support

From: Cornelia Huck <cohuck@redhat.com>
To: Halil Pasic <pasic@linux.ibm.com>
Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Sebastian Ott <sebott@linux.ibm.com>,
	virtualization@lists.linux-foundation.org,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	Thomas Huth <thuth@redhat.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Viktor Mihajlovski <mihajlov@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Farhan Ali <alifm@linux.ibm.com>,
	Eric Farman <farman@linux.ibm.com>
Subject: Re: [PATCH 06/10] s390/cio: add basic protected virtualization support
Date: Mon, 13 May 2019 11:41:36 +0200	[thread overview]
Message-ID: <20190513114136.783c851c.cohuck@redhat.com> (raw)
In-Reply-To: <20190426183245.37939-7-pasic@linux.ibm.com>

On Fri, 26 Apr 2019 20:32:41 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> As virtio-ccw devices are channel devices, we need to use the dma area
> for any communication with the hypervisor.
> 
> This patch addresses the most basic stuff (mostly what is required for
> virtio-ccw), and does take care of QDIO or any devices.

"does not take care of QDIO", surely? (Also, what does "any devices"
mean? Do you mean "every arbitrary device", perhaps?)

> 
> An interesting side effect is that virtio structures are now going to
> get allocated in 31 bit addressable storage.

Hm...

> 
> Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
> ---
>  arch/s390/include/asm/ccwdev.h   |  4 +++
>  drivers/s390/cio/ccwreq.c        |  8 ++---
>  drivers/s390/cio/device.c        | 65 +++++++++++++++++++++++++++++++++-------
>  drivers/s390/cio/device_fsm.c    | 40 ++++++++++++-------------
>  drivers/s390/cio/device_id.c     | 18 +++++------
>  drivers/s390/cio/device_ops.c    | 21 +++++++++++--
>  drivers/s390/cio/device_pgid.c   | 20 ++++++-------
>  drivers/s390/cio/device_status.c | 24 +++++++--------
>  drivers/s390/cio/io_sch.h        | 21 +++++++++----
>  drivers/s390/virtio/virtio_ccw.c | 10 -------
>  10 files changed, 148 insertions(+), 83 deletions(-)

(...)

> diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> index 6d989c360f38..bb7a92316fc8 100644
> --- a/drivers/s390/virtio/virtio_ccw.c
> +++ b/drivers/s390/virtio/virtio_ccw.c
> @@ -66,7 +66,6 @@ struct virtio_ccw_device {
>  	bool device_lost;
>  	unsigned int config_ready;
>  	void *airq_info;
> -	u64 dma_mask;
>  };
>  
>  struct vq_info_block_legacy {
> @@ -1255,16 +1254,7 @@ static int virtio_ccw_online(struct ccw_device *cdev)
>  		ret = -ENOMEM;
>  		goto out_free;
>  	}
> -
>  	vcdev->vdev.dev.parent = &cdev->dev;
> -	cdev->dev.dma_mask = &vcdev->dma_mask;
> -	/* we are fine with common virtio infrastructure using 64 bit DMA */
> -	ret = dma_set_mask_and_coherent(&cdev->dev, DMA_BIT_MASK(64));
> -	if (ret) {
> -		dev_warn(&cdev->dev, "Failed to enable 64-bit DMA.\n");
> -		goto out_free;
> -	}

This means that vring structures now need to fit into 31 bits as well,
I think? Is there any way to reserve the 31 bit restriction for channel
subsystem structures and keep vring in the full 64 bit range? (Or am I
fundamentally misunderstanding something?)

> -
>  	vcdev->config_block = kzalloc(sizeof(*vcdev->config_block),
>  				   GFP_DMA | GFP_KERNEL);
>  	if (!vcdev->config_block) {