Re: [PATCH v3 7/8] virtio/s390: use DMA memory for ccw I/O and classic notifiers

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 29 May 2019 14:26:56 +0200
Michael Mueller <mimu@linux.ibm.com> wrote:

> From: Halil Pasic <pasic@linux.ibm.com>
> 
> Before virtio-ccw could get away with not using DMA API for the pieces of
> memory it does ccw I/O with. With protected virtualization this has to
> change, since the hypervisor needs to read and sometimes also write these
> pieces of memory.
> 
> The hypervisor is supposed to poke the classic notifiers, if these are
> used, out of band with regards to ccw I/O. So these need to be allocated
> as DMA memory (which is shared memory for protected virtualization
> guests).
> 
> Let us factor out everything from struct virtio_ccw_device that needs to
> be DMA memory in a satellite that is allocated as such.
> 
> Note: The control blocks of I/O instructions do not need to be shared.
> These are marshalled by the ultravisor.
> 
> Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
> Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
> ---
>  drivers/s390/virtio/virtio_ccw.c | 177 +++++++++++++++++++++------------------
>  1 file changed, 96 insertions(+), 81 deletions(-)
> 

(...)

> @@ -176,6 +180,22 @@ static struct virtio_ccw_device *to_vc_device(struct virtio_device *vdev)
>  	return container_of(vdev, struct virtio_ccw_device, vdev);
>  }
>  
> +static inline void *__vc_dma_alloc(struct virtio_device *vdev, size_t size)
> +{
> +	return ccw_device_dma_zalloc(to_vc_device(vdev)->cdev, size);
> +}
> +
> +static inline void __vc_dma_free(struct virtio_device *vdev, size_t size,
> +				 void *cpu_addr)
> +{
> +	return ccw_device_dma_free(to_vc_device(vdev)->cdev, cpu_addr, size);
> +}
> +
> +#define vc_dma_alloc_struct(vdev, ptr) \
> +	({ptr = __vc_dma_alloc(vdev, sizeof(*(ptr))); })
> +#define vc_dma_free_struct(vdev, ptr) \
> +	__vc_dma_free(vdev, sizeof(*(ptr)), (ptr))
> +

I *still* don't like these #defines (and the __vc_dma_* functions), as I
already commented last time. I think they make it harder to follow the
code.

>  static void drop_airq_indicator(struct virtqueue *vq, struct airq_info *info)
>  {
>  	unsigned long i, flags;
> @@ -336,8 +356,7 @@ static void virtio_ccw_drop_indicator(struct virtio_ccw_device *vcdev,
>  	struct airq_info *airq_info = vcdev->airq_info;
>  
>  	if (vcdev->is_thinint) {
> -		thinint_area = kzalloc(sizeof(*thinint_area),
> -				       GFP_DMA | GFP_KERNEL);
> +		vc_dma_alloc_struct(&vcdev->vdev, thinint_area);

Last time I wrote:

"Any reason why this takes a detour via the virtio device? The ccw
 device is already referenced in vcdev, isn't it?

thinint_area = ccw_device_dma_zalloc(vcdev->cdev, sizeof(*thinint_area));

 looks much more obvious to me."

It still seems more obvious to me.

>  		if (!thinint_area)
>  			return;
>  		thinint_area->summary_indicator =