Re: [PATCH v2 11/16] vfio/ccw: read only one Format-1 IDAW

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 12/20/22 12:10 PM, Eric Farman wrote:
> The intention is to read the first IDAW to determine the starting
> location of an I/O operation, knowing that the second and any/all
> subsequent IDAWs will be aligned per architecture. But, this read
> receives 64-bits of data, which is the size of a Format-2 IDAW.
> 
> In the event that Format-1 IDAWs are presented, adjust the size
> of the read to 32-bits. The data will end up occupying the upper
> word of the target iova variable, so shift it down to the lower
> word for use as an adddress. (By definition, this IDAW format
> uses a 31-bit address, so the "sign" bit will always be off and
> there is no concern about sign extension.)
> 
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
>  drivers/s390/cio/vfio_ccw_cp.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
> index 9d74e0b74da7..29d1e418b2e2 100644
> --- a/drivers/s390/cio/vfio_ccw_cp.c
> +++ b/drivers/s390/cio/vfio_ccw_cp.c
> @@ -509,6 +509,7 @@ static int ccw_count_idaws(struct ccw1 *ccw,
>  	struct vfio_device *vdev =
>  		&container_of(cp, struct vfio_ccw_private, cp)->vdev;
>  	u64 iova;
> +	int size = cp->orb.cmd.c64 ? sizeof(u64) : sizeof(u32);
>  	int ret;
>  	int bytes = 1;
>  
> @@ -516,11 +517,15 @@ static int ccw_count_idaws(struct ccw1 *ccw,
>  		bytes = ccw->count;
>  
>  	if (ccw_is_idal(ccw)) {
> -		/* Read first IDAW to see if it's 4K-aligned or not. */
> -		/* All subsequent IDAws will be 4K-aligned. */
> -		ret = vfio_dma_rw(vdev, ccw->cda, &iova, sizeof(iova), false);
> +		/* Read first IDAW to check its starting address. */
> +		/* All subsequent IDAWs will be 2K- or 4K-aligned. */
> +		ret = vfio_dma_rw(vdev, ccw->cda, &iova, size, false);
>  		if (ret)
>  			return ret;
> +
> +		/* Format-1 IDAWs only occupy the first int */

nit: s/int/32 bits/

Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>

> +		if (!cp->orb.cmd.c64)
> +			iova = iova >> 32;
>  	} else {
>  		iova = ccw->cda;
>  	}