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Date: Mon, 13 May 2019 15:54:19 +0200
From: Cornelia Huck <cohuck@redhat.com>
Subject: Re: [PATCH 09/10] virtio/s390: use DMA memory for ccw I/O and
 classic notifiers
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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>
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On Fri, 26 Apr 2019 20:32:44 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> 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>
> ---
>  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);
> +}

Hm, why do these use leading underscores?

Also, maybe make the _free function safe for NULL to simplify the
cleanup paths?


> +
> +#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 find these a bit ugly... does adding a wrapper help that much?

> +
>  static void drop_airq_indicator(struct virtqueue *vq, struct airq_info *info)
>  {
>  	unsigned long i, flags;