Re: [PATCH 10/10] virtio/s390: make airq summary indicators DMA

[Pierre Morel <pmorel@xxxxxxxxxxxxx>]

On 26/04/2019 20:32, Halil Pasic wrote:
> Hypervisor needs to interact with the summary indicators, so these
> need to be DMA memory as well (at least for protected virtualization
> guests).
>
> Signed-off-by: Halil Pasic <pasic@xxxxxxxxxxxxx>
> ---
>   drivers/s390/virtio/virtio_ccw.c | 24 +++++++++++++++++-------
>   1 file changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> index 613b18001a0c..6058b07fea08 100644
> --- a/drivers/s390/virtio/virtio_ccw.c
> +++ b/drivers/s390/virtio/virtio_ccw.c
> @@ -140,11 +140,17 @@ static int virtio_ccw_use_airq = 1;
>   
>   struct airq_info {
>   	rwlock_t lock;
> -	u8 summary_indicator;
> +	u8 summary_indicator_idx;
>   	struct airq_struct airq;
>   	struct airq_iv *aiv;
>   };
>   static struct airq_info *airq_areas[MAX_AIRQ_AREAS];
> +static u8 *summary_indicators;
> +
> +static inline u8 *get_summary_indicator(struct airq_info *info)
> +{
> +	return summary_indicators + info->summary_indicator_idx;
> +}
>   
>   #define CCW_CMD_SET_VQ 0x13
>   #define CCW_CMD_VDEV_RESET 0x33
> @@ -225,7 +231,7 @@ static void virtio_airq_handler(struct airq_struct *airq)
>   			break;
>   		vring_interrupt(0, (void *)airq_iv_get_ptr(info->aiv, ai));
>   	}
> -	info->summary_indicator = 0;
> +	*(get_summary_indicator(info)) = 0;
>   	smp_wmb();
>   	/* Walk through indicators field, summary indicator not active. */
>   	for (ai = 0;;) {
> @@ -237,7 +243,8 @@ static void virtio_airq_handler(struct airq_struct *airq)
>   	read_unlock(&info->lock);
>   }
>   
> -static struct airq_info *new_airq_info(void)
> +/* call with airq_areas_lock held */
> +static struct airq_info *new_airq_info(int index)
>   {
>   	struct airq_info *info;
>   	int rc;
> @@ -252,7 +259,8 @@ static struct airq_info *new_airq_info(void)
>   		return NULL;
>   	}
>   	info->airq.handler = virtio_airq_handler;
> -	info->airq.lsi_ptr = &info->summary_indicator;
> +	info->summary_indicator_idx = index;
> +	info->airq.lsi_ptr = get_summary_indicator(info);
>   	info->airq.lsi_mask = 0xff;
>   	info->airq.isc = VIRTIO_AIRQ_ISC;
>   	rc = register_adapter_interrupt(&info->airq);
> @@ -273,8 +281,9 @@ static unsigned long get_airq_indicator(struct virtqueue *vqs[], int nvqs,
>   	unsigned long bit, flags;
>   
>   	for (i = 0; i < MAX_AIRQ_AREAS && !indicator_addr; i++) {
> +		/* TODO: this seems to be racy */

yes, my opinions too, was already racy, in my opinion, we need another 
patch in another series to fix this.

However, not sure about the comment.

>   		if (!airq_areas[i])
> -			airq_areas[i] = new_airq_info();
> +			airq_areas[i] = new_airq_info(i);
>   		info = airq_areas[i];
>   		if (!info)
>   			return 0;
> @@ -359,7 +368,7 @@ static void virtio_ccw_drop_indicator(struct virtio_ccw_device *vcdev,
>   		if (!thinint_area)
>   			return;
>   		thinint_area->summary_indicator =
> -			(unsigned long) &airq_info->summary_indicator;
> +			(unsigned long) get_summary_indicator(airq_info);
>   		thinint_area->isc = VIRTIO_AIRQ_ISC;
>   		ccw->cmd_code = CCW_CMD_SET_IND_ADAPTER;
>   		ccw->count = sizeof(*thinint_area);
> @@ -624,7 +633,7 @@ static int virtio_ccw_register_adapter_ind(struct virtio_ccw_device *vcdev,
>   	}
>   	info = vcdev->airq_info;
>   	thinint_area->summary_indicator =
> -		(unsigned long) &info->summary_indicator;
> +		(unsigned long) get_summary_indicator(info);
>   	thinint_area->isc = VIRTIO_AIRQ_ISC;
>   	ccw->cmd_code = CCW_CMD_SET_IND_ADAPTER;
>   	ccw->flags = CCW_FLAG_SLI;
> @@ -1500,6 +1509,7 @@ static int __init virtio_ccw_init(void)
>   {
>   	/* parse no_auto string before we do anything further */
>   	no_auto_parse();
> +	summary_indicators = cio_dma_zalloc(MAX_AIRQ_AREAS);
>   	return ccw_driver_register(&virtio_ccw_driver);
>   }
>   device_initcall(virtio_ccw_init);



--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany