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

Matthew Rosato
2022-12-16T21:05:56Z

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)) {