Re: [PATCH v1 09/16] vfio/ccw: populate page_array struct inline

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

On 11/21/22 4:40 PM, Eric Farman wrote:
> There are two possible ways the list of addresses that get passed
> to vfio are calculated. One is from a guest IDAL, which would be
> an array of (probably) non-contiguous addresses. The other is
> built from contiguous pages that follow the starting address
> provided by ccw->cda.
> 
> page_array_alloc() attempts to simplify things by pre-populating
> this array from the starting address, but that's not needed for
> a CCW with an IDAL anyway so doesn't need to be in the allocator.
> Move it to the caller in the non-IDAL case, since it will be
> overwritten when reading the guest IDAL.
> 
> Remove the initialization of the pa_page output pointers,
> since it won't be explicitly needed for either case.
> 
> Signed-off-by: Eric Farman <farman@linux.ibm.com>

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

> ---
>  drivers/s390/cio/vfio_ccw_cp.c | 22 +++++-----------------
>  1 file changed, 5 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
> index 66e890441163..a30f26962750 100644
> --- a/drivers/s390/cio/vfio_ccw_cp.c
> +++ b/drivers/s390/cio/vfio_ccw_cp.c
> @@ -42,7 +42,6 @@ struct ccwchain {
>  /*
>   * page_array_alloc() - alloc memory for page array
>   * @pa: page_array on which to perform the operation
> - * @iova: target guest physical address
>   * @len: number of pages that should be pinned from @iova
>   *
>   * Attempt to allocate memory for page array.
> @@ -56,10 +55,8 @@ struct ccwchain {
>   *   -EINVAL if pa->pa_nr is not initially zero, or pa->pa_iova is not NULL
>   *   -ENOMEM if alloc failed
>   */
> -static int page_array_alloc(struct page_array *pa, u64 iova, unsigned int len)
> +static int page_array_alloc(struct page_array *pa, unsigned int len)
>  {
> -	int i;
> -
>  	if (pa->pa_nr || pa->pa_iova)
>  		return -EINVAL;
>  
> @@ -78,13 +75,6 @@ static int page_array_alloc(struct page_array *pa, u64 iova, unsigned int len)
>  		return -ENOMEM;
>  	}
>  
> -	pa->pa_iova[0] = iova;
> -	pa->pa_page[0] = NULL;
> -	for (i = 1; i < pa->pa_nr; i++) {
> -		pa->pa_iova[i] = pa->pa_iova[i - 1] + PAGE_SIZE;
> -		pa->pa_page[i] = NULL;
> -	}
> -
>  	return 0;
>  }
>  
> @@ -548,7 +538,7 @@ static int ccwchain_fetch_ccw(struct ccw1 *ccw,
>  	 * required for the data transfer, since we only only support
>  	 * 4K IDAWs today.
>  	 */
> -	ret = page_array_alloc(pa, iova, idaw_nr);
> +	ret = page_array_alloc(pa, idaw_nr);
>  	if (ret < 0)
>  		goto out_free_idaws;
>  
> @@ -565,11 +555,9 @@ static int ccwchain_fetch_ccw(struct ccw1 *ccw,
>  		for (i = 0; i < idaw_nr; i++)
>  			pa->pa_iova[i] = idaws[i];
>  	} else {
> -		/*
> -		 * No action is required here; the iova addresses in page_array
> -		 * were initialized sequentially in page_array_alloc() beginning
> -		 * with the contents of ccw->cda.
> -		 */
> +		pa->pa_iova[0] = iova;
> +		for (i = 1; i < pa->pa_nr; i++)
> +			pa->pa_iova[i] = pa->pa_iova[i - 1] + PAGE_SIZE;
>  	}
>  
>  	if (ccw_does_data_transfer(ccw)) {